Use of data imputation tools to reconstruct incomplete air quality datasets: A case-study in Temuco, Chile Atmos. Environ. (IF 3.708) Pub Date : 2018-12-07 María Elisa Quinteros, Siyao Lu, Carola Blazquez, Juan Pablo Cárdenas-R, Ximena Ossa, Juana-María Delgado-Saborit, Roy M. Harrison, Pablo Ruiz-Rudolph
Missing data from air quality datasets is a common problem, but it is much more severe in small cities or localities. This poses a great challenge for environmental epidemiology as high exposures to pollutants worldwide occur in these settings and gaps in datasets hinder health studies that could later inform local and international policies. Here, we propose the use of imputation methods as a tool to reconstruct air quality datasets and applied this approach to an air quality dataset in Temuco, a mid-size city in Chile as a case-study. We attempted to reconstruct the database comparing five approaches: mean imputation, conditional mean imputation, K-Nearest Neighbor imputation, multiple imputation and Bayesian Principal Component Analysis imputation. As a base for the imputation methods, linear regression models were fitted for PM2.5 against other air quality and meteorological variables. Methods were challenged against validation sets where data was removed artificially. Imputation methods were able to reconstruct the dataset with good performance in terms of completeness, errors, and bias, even when challenged against the validations sets. The performance improved when including covariates from a second monitoring station in Temuco. K-Nearest Neighbor imputation showed slightly better performance than multiple imputation for error (25% vs. 27%) and bias (2.1% vs. 3.9%), but presented lower completeness (70% vs. 100%). In summary, our results show that the imputation methods can be to a certain extent successful in reconstructing air quality dataset in a real-life situation.
Impact of particle chemical composition and water content on the photolytic reduction of particle-bound mercury Atmos. Environ. (IF 3.708) Pub Date : 2018-12-03 Chunyan Deng, Yindong Tong, Long Chen, Wen Yuan, Yingli Sun, Jinling Li, Xuejun Wang, Wei Zhang, Huiming Lin, Han Xie, Xiaoge Bu
The current understanding of Hg(II) photolytic reduction in atmospheric particles is inadequate. This study addresses the impacts of the particle chemical composition (e.g. anions, trace elements, and carbon concentrations) and water content on the Hg(II) photolytic reduction process under ambient conditions. The results showed that Hg(II) in particles was significantly reduced under irradiation and this process could be prohibited by certain heavy metals and promoted by increasing water content in particles. Negligible evolved Hg(0) amount was observed from particles under dark condition (occupying for <0.5% in particle-bound mercury). With a 10% increase in water content, the corresponding Hg(II) reduction rate increased by 1–5% after 30 min of light exposure (at an irradiance of 1000 W/m2). The Hg(II) photolytic reduction in particles generally correlates with first-order reaction kinetics, with a half-life in a clear sky of 1.6 and 12.2 h for particles collected in the summer and winter, respectively. This study demonstrates that Hg(0) evolves quickly under light exposure regardless of whether the particles are wet or dry, and these processes need to be specified in future atmospheric Hg modelling.
Establishing a model organic film of low volatile compound mixture on aqueous aerosol surface Atmos. Environ. (IF 3.708) Pub Date : 2018-12-01 Siyang Li, Shumin Cheng, Lin Du, Wenxing Wang
Long chain fatty acids and alcohols are low volatile species in continental and marine aerosols. We established a surface film model by Langmuir trough to investigate the interfacial properties of sea salts droplets coated by surface active molecules—stearic acid (SA), oleic acid (OA), 1-octadecanol (C18OH) and their mixtures. The aim of this work was to verify the impact of the head group, saturation degree, mixing ratio of different surfactants on miscibility and stability between these compounds in monolayers at the air–water interface. Compared to the organic-coated water droplets, the surface properties of mixed fatty acid and alcohol-coated aqueous sea salt particles are substantially different. Mixed SA/C18OH monolayers are less stable than pure SA or C18OH monolayer at high surface pressure. From the point of view of the geometry, steric hindrance of unsaturated chain is the crucial factor in loose packing of OA monolayer. The negative values of excess mixing areas (ΔAex) for OA/C18OH monolayer on artificial seawater result from the attractive interaction between tail groups. The maximum negative value of excess Gibbs free energies (ΔGex) appears at the equimolecular OA and C18OH. Surface pressure−area (π–A) isotherm combined with equilibrium spreading pressure (ESP) confirms that the tightly packed monolayer formed by C18OH molecules can minimize water evaporation rate of the potential droplet. Different surface properties of organic films coated on aqueous aerosol must have a significant impact on interaction droplet growth. The interactions between fatty acid and alcohol at the air-water interface provide an insight into the nucleation and growth mechanism of droplets covered by film-forming species.
Machine learning-based rapid response tools for regional air pollution modelling Atmos. Environ. (IF 3.708) Pub Date : 2018-11-24 D. Xiao, F. Fang, J. Zheng, C.C. Pain, I.M. Navon
A parameterised non-intrusive reduced order model (P-NIROM) based on proper orthogonal decomposition (POD) and machine learning methods has been firstly developed for model reduction of pollutant transport equations. Our motivation is to provide rapid response urban air pollution predictions and controls. The varying parameters in the P-NIROM are pollutant sources. The training data sets are obtained from the high fidelity modelling solutions (called snapshots) for selected parameters (pollutant sources, here) over the parameter space . From these training data sets, the machine learning method is used to generate the relationship between the reduced solutions and inputs (pollutant sources) over . Furthermore a set of hyper-surface functions associated with each POD basis function is constructed for representing the fluid dynamics over the reduced space. The accuracy of the P-NIROM is highly dependent on the quality of the training set, here obtained from the high fidelity model. Over existing machine learning methods, the P-NIROM algorithm proposed here has the advantages that (1) it is combined with NIROM, thus providing rapid and reasonably accurate solutions; and (2) it is a robust and efficient approach for representation of any parametrised partial differential equations as the model parameters/inputs vary. In this study, we demonstrate the way how to implement the P-NIROM for the pollutant transport equation (but not limited to due to its robustness). Its predictive capability is illustrated in a three-dimensional (3-D) simulation of power plant plumes over a large region in China, where the varying parameters are the emission intensity at three locations. Results indicate that in comparison to the high fidelity model, the CPU cost is reduced by factor up to five orders of magnitude while reasonable accuracy remains.
Validation of ammonia diffusive and pumped samplers in a controlled atmosphere test facility using traceable Primary Standard Gas Mixtures Atmos. Environ. (IF 3.708) Pub Date : 2018-11-22 Nicholas A. Martin, Valerio Ferracci, Nathan Cassidy, Josh Hook, Ross M. Battersby, Elena Amico di Meane, Yuk S. Tang, Amy C.M. Stephens, Sarah R. Leeson, Matthew R. Jones, Christine F. Braban, Linda Gates, Markus Hangartner, Jean-Marc Stoll, Paolo Sacco, Diego Pagani, John A. Hoffnagle, Eva Seitler
We report the determination of ammonia (NH3) diffusive sampling rates for six different designs of commercial diffusive samplers (CEH ALPHA sampler, Gradko diffusion tube, Gradko DIFRAM-400, Passam ammonia sampler, and ICS Maugeri Radiello radial sampler (blue and white turbulence barriers)), together with the validation test results for a pumped sampler (CEH DELTA denuder). The devices were all exposed in the UK's National Physical Laboratory's (NPL) controlled atmosphere test facility (CATFAC). For each of the seven diffusive sampler exposure tests there were traceable concentrations of ammonia (in the range 3–25 μg m−3) generated under well-defined conditions of temperature, relative humidity and wind speed, which are applicable to a variety of ambient monitoring environments. The sampler exposure time at each concentration was 28 days, except for the radial devices, which were exposed for 14 days. The work relied on the dilution of newly developed stable Primary Standard Gas Mixtures (PSMs) prepared by gravimetry in passivated gas cylinders as a method of improving the metrological traceability of ammonia measurements. The exposed diffusive samplers were sent blind to the participants for analysis and the reported NH3 concentrations were then compared against the known reference concentration. From the results for each sampler type a diffusive sampling rate was calculated and compared against the rate used routinely by the participants. Some measurement results were in good agreement with the known traceable reference concentration (particularly for one diffusive sampler design (ALPHA)), while other devices exhibited over-reading and under-reading (each with a clear bias). The new diffusive sampling rates determined in the laboratory study were then applied to measurements in a field comparison campaign, and this was found to deliver an improvement in agreement between the different devices deployed.
Characterization of submicron aerosol chemical composition and sources in the coastal area of Central Chile Atmos. Environ. (IF 3.708) Pub Date : 2018-11-22 S. Saarikoski, F. Reyes, Y. Vázquez, M. Tagle, H. Timonen, M. Aurela, S. Carbone, D.R. Worsnop, R. Hillamo, P. Oyola
Chemical characteristics and the sources of submicron particles (<1 μm in diameter) were investigated in Valle Alegre, the coastal area of Central Chile. The chemical composition of particles was studied by using a Soot particle Aerosol Mass Spectrometer and Multi-Angle Absorption Photometer. Submicron particles were dominated by organics (42% of mass) and sulfate (39% of mass) while the mass fractions of ammonium, nitrate and black carbon were much smaller (13, 2 and 4% of mass, respectively). Additionally, several metals (V, Zn, Fe, Cd, Cu, K, Na and Mg) were detected in submicron particles and also some of their inorganic salts (e.g. NaCl+, MgCl2+, CaCl2+, KCl+ and KNO3+). The sources of particles were examined by using Positive Matrix Factorization (PMF). Organic aerosol (OA) was divided into five factors by using PMF; hydrocarbon-like OA (HOA), biomass burning OA (BBOA), low-volatility oxygenated OA (LV-OOA), semi-volatile OA (SV-OOA) and marine oxygenated OOA (MOOA). Oxygenated factors (LV-OOA; SV-OOA and MOOA) comprised 75% of total OA with LV-OOA being the dominant factor (38% of OA). Sulfate had two major sources in Valle Alegre; ∼70% of sulfate was related to anthropogenic sources through the oxidation of gas phase SO2 whereas ∼24% of sulfate was associated with biogenic origin related to the oxidation of dimethyl sulfide in the marine environment. Regarding total submicron particle mass (campaign-average 9.5 μg m−3), the contribution of anthropogenic sources was at least as large as that of biogenic origin.
Rate coefficients of reactions of 1-chlorocyclopentene with tropospheric oxidants at 298 K Atmos. Environ. (IF 3.708) Pub Date : 2018-11-20 Asmita Sharma, Mohini P. Walavalkar, Ankur Saha, Monali Kawade, Awadhesh Kumar, Prakash D. Naik
The reactions of 1-chlorocyclopentene with tropospheric oxidants, Cl, OH and O3 are studied to measure the rate coefficients at 298 K and 800 Torr of N2 using the relative rate method with butene, cyclopentene and butane as references. The concentrations of the organics are measured by Gas Chromatograpy technique. The measured average rate coefficient values of kCl, kOH and kO3 (in cm3 molecule−1 s−1) are (3.51 ± 1.26) x 10−10, (5.97 ± 1.08) x 10−11 and (1.50 ± 0.19) x 10−17, respectively. In addition, the rate coefficient for reaction of OH with 1-chlorocyclopentene at 298 K and 30 Torr was also measured using an absolute method of laser photolysis-laser induced fluorescence technique, and the kOH value is found to be (6.01 ± 0.70) x 10−11 cm3 molecule−1 s−1. The stable products formed during the reaction of Cl, OH and O3 initiated oxidation of the 1-chlorocyclopentene in presence of air are characterized by GCMS. The abstraction and addition products are identified among them, the latter are found to be major products. The experimental results are supported by molecular orbital calculations, and abstraction of the allylic hydrogen atoms is predicted to be the major abstraction channel. Calculations predict the preferential addition of chlorine atom to the carbon atom of the unsaturation center not having Cl attached to it. The rate coefficients of 1-chlorocyclopentene are compared with that of cyclopentene and substituted cyclopentene to understand the effect of substituent Cl on the reactivity. The measured rate coefficients have been used to calculate tropospheric lifetime of the compound to be 316, 2 and 26 h for Cl, OH and O3, respectively. Based on these values, the major degradation pathway of 1-chlorocyclopentene is suggested to be its reaction with OH. Atmospheric impact of these molecules is local as tropospheric lifetime (τ) < 2 h. Using the tropospheric lifetime of 1-chlorocyclopentene, and its IR absorption cross-section in tropospheric IR window and under the assumption of a well mixed atmosphere, the radiative forcing of 1-chlorocyclopentene was estimated to be 22.41 mWm−2 ppb−1, and the global warming potentials for 20 and 100 years time horizon were calculated to be 0.01 and 0.003, respectively.
Comparison of nitrogen deposition across different land use types in agro-pastoral catchments of western China and Mongolia Atmos. Environ. (IF 3.708) Pub Date : 2018-11-20 Jinling Lv, Andreas Buerkert, Katherine B. Benedict, Guojun Liu, Chaoyan Lv, Xuejun Liu
Very few comparative studies on atmospheric dry and wet nitrogen (N) deposition have been conducted in agro-pastoral catchment areas. In an effort to fill this knowledge gap, three interconnected land use types (cropland, mountain pasture, and plain pasture) with six sampling sites (Chinese cropland (CC), Chinese mountain pasture (CM), Chinese plain pasture (CP) Mongolia cropland (MC), Mongolia mountain pasture (MM) and Mongolia plain pasture (MP)) were selected in the transboundary regions of northwest China and western Mongolia. During 16 months from May 2014 to September 2015 atmospheric and precipitation samples were collected to assess levels of nitrogen deposition. Cropland had the highest NO3−N (1.0 mg N L−1 in China and 1.2 mg N L−1 in Mongolia) and NH4+-N concentrations (1.6 mg N L−1 in China and 2.0 mg N L−1 in Mongolia) in our six sampling sites. The CC experienced the highest wet deposition (5.2 kg N ha−1 yr−1), followed by MM pasture (3.2 kg N ha−1 yr−1) while wet deposition in other sites ranged from 2.1 to 2.8 kg N ha−1 yr−1. The ambient concentrations of NH3, NO2 and dry N deposition were significant higher in cropland than being other land use with 3.0, 3.8 and 1.2 μg N m−3 respectively in China and 2.2, 2.8 and 0.6 μg N m−3 respectively in Mongolia. The highest total N deposition was at CC (14.5 kg N ha−1 yr−1) and MC (9.4 kg N ha−1 yr−1), followed by the mountain pasture (5.8–6.8 kg N ha−1 yr−1), and the plains pasture (5.6–5.7 kg N ha−1 yr−1). Overall, agro-pastoral catchments areas had relatively low total N deposition compared to other studies, and cropland had the highest wet and dry N deposition than mountain and plain pastures, and dry N deposition absolutely dominated the percentage (64–70% in cropland and 53–64% in pasture areas) of total atmospheric N deposition. Comparing the total N deposition in China and Mongolia, we found the CC had 54% higher value than in MC while the reverse was true for mountain pastures Mongolia received 17% more N.
Formation of atmospheric molecular clusters consisting of methanesulfonic acid and sulfuric acid: Insights from flow tube experiments and cluster dynamics simulations Atmos. Environ. (IF 3.708) Pub Date : 2018-11-20 Hui Wen, Chun-Yu Wang, Zhong-Quan Wang, Xiao-Fei Hou, Ya-Juan Han, Yi-Rong Liu, Shuai Jiang, Teng Huang, Wei Huang
In coastal regions and ocean areas, methanesulfonic acid (MSA; CH3SO3H) is present in considerable concentrations in the gas-phase and aerosols. It has been shown that MSA could contribute to growth and possibly form initial molecular cluster, which may lead to aerosol formation. However, quantitative concentrations and thermodynamic properties of MSA and sulfuric acid (SA; H2SO4) in the presence of water (W; H2O) remain largely uncertain. In this study, flow tube reactor was used to investigate the effects of each reactant on new particle formation (NPF) in a multi-component system consisting of MSA, SA, and W. Particles were measured for different combinations of reactants. It showed that a different order for reactant addition led to different experimental results, where the added MSA vapor to the SA-W binary system presented an obvious bimodal structure, for ternary system with SA added to the MSA-W, the similar bimodal phenomenon was not observed. The composition of clusters in the air flow was further analyzed by the commercial Atmospheric Pressure Interface Time-of-Flight Mass Spectrometer (APi-TOF-MS, Tofwerk AG), which is equipped with a homemade chemical ionization (CI) source, mass peaks corresponding to clusters that contain smaller MSA or SA molecules were clearly observed, indicating that these clusters are exist and stable. In addition, quantum chemistry calculation-based evaporation rate values were applied in a cluster dynamics model to yield formation rates of 2.6 × 102 cm−3 s−1 and cluster concentrations under different simulation conditions. This study could provide some insight into how acids interact in the atmosphere.
Retrieval of aerosol profiles by Raman lidar with dynamic determination of the lidar equation reference height Atmos. Environ. (IF 3.708) Pub Date : 2018-11-20 Jian Li, Chengcai Li, Jianping Guo, Jing Li, Wangshu Tan, Ling Kang, Dandan Chen, Tao Song, Lin Liu
A reference height that often needs to be assumed in aerosol retrieval from Raman lidar tends to cause high uncertainty in retrieving the vertical distribution of aerosol optical properties. Here, a novel method is proposed to determine the height-revolved reference height, which is then used to retrieve aerosols from Raman lidar. This method can automatically avoid the atmospheric layers with the presence of aerosols, clouds and low signal to noise ratio (SNR). Based on elastic (at 355 nm) and inelastic (at 387 nm) signals collected during the period from 5 December 2016 to 5 March 2017 by a ground-based Raman lidar in Beijing, China, the aerosol optical properties, such as extinction coefficient, backscattering coefficient and lidar ratio have been successfully retrieved. Results show that the averaged nighttime aerosol optic depth (AOD) from Raman lidar is in good agreement with early morning AOD retrieved from a collocated sunphotometer. The AOD exhibits a strong diurnal variation with a peak at 1500 Beijing time. On average, the nighttime AOD at 355 nm is 0.32, whereas the daytime AOD is 0.72 over Beijing during the study period. The column averaged lidar ratio is 44 sr at 355 nm, roughly consistent with previous studies. Our findings shed light on the pathways towards improving the retrieval of vertical distribution of aerosols optical properties during nighttime.
Using gap-filled MAIAC AOD and WRF-Chem to estimate daily PM2.5 concentrations at 1 km resolution in the Eastern United States Atmos. Environ. (IF 3.708) Pub Date : 2018-11-20 Daniel L. Goldberg, Pawan Gupta, Kai Wang, Chinmay Jena, Yang Zhang, Zifeng Lu, David G. Streets
To link short-term exposures of air pollutants to health outcomes, scientists must use high temporal and spatial resolution estimates of PM2.5 concentrations. In this work, we develop a daily PM2.5 product at 1 × 1 km2 spatial resolution across the eastern United States (east of 90° W) with the aid of 1 × 1 km2 MAIAC aerosol optical depth (AOD) data, 36 × 36 km2 WRF-Chem output, 1 × 1 km2 land-use type from the National Land Cover Database, and 0.125° × 0.125° ERA-Interim re-analysis meteorology. A gap-filling technique is applied to MAIAC AOD data to construct robust daily estimates of AOD when the satellite data are missing (e.g., areas obstructed by clouds or snow cover). The input data are incorporated into a multiple-linear regression model trained to surface observations of PM2.5 from the EPA Air Quality System (AQS) monitoring network. The model generates a high-fidelity estimate (r2 = 0.75 using a 10-fold random cross-validation) of daily PM2.5 throughout the eastern United States. Of the inputs to the statistical model, WRF-Chem output (r2 = 0.66) is the most important contributor to the skill of the model. MAIAC AOD is also a strong contributor (r2 = 0.52). Daily PM2.5 output from our statistical model can be easily integrated into county-level epidemiological studies. The novelty of this project is that we are able to simulate PM2.5 in a computationally efficient manner that is constrained to ground monitors, satellite data, and chemical transport model output at high spatial resolution (1 × 1 km2) without sacrificing the temporal resolution (daily) or spatial coverage (>2,000,000 km2).
MAX-DOAS measurements and vertical profiles of glyoxal and formaldehyde in Madrid, Spain Atmos. Environ. (IF 3.708) Pub Date : 2018-11-20 Nuria Benavent, David Garcia-Nieto, Shanshan Wang, Alfonso Saiz-Lopez
Glyoxal (CHOCHO) and formaldehyde (HCHO) are organic trace gases that play an important role in tropospheric chemistry as oxidation products of a number of volatile organic compounds (VOCs). In this study, we report year-round daytime measurements of glyoxal and formaldehyde in the urban atmosphere of Madrid, Spain. Their vertical concentration profiles were retrieved using the Multi AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) technique and a Radiative Transfer Model (RTM) that simulates solar photon paths through the atmosphere. The diurnal variations of HCHO show two distinct peaks during the day, in the early morning and late afternoon in spring and summer, while the second peak is shifted towards noon in autumn and winter, due to lower photolysis rates and more effective boundary layer accumulation of HCHO in those seasons. The HCHO surface mixing ratios range from 6 ppbv to 27 ppbv in spring-summer and from 10 ppbv to 30 ppbv in autumn-winter. Monthly hourly-averaged glyoxal surface mixing ratios in the early morning show higher values during winter, 2 ppbv, than in summer, 0.7 ppbv. We also evaluated the ratio between glyoxal and formaldehyde (RGF) surface mixing ratios, as an indicator of the nature of VOCs precursors. The RGF was also correlated with the measured NO2 -which represents a direct signal of anthropogenic emissions-along with the VOCs emission inventories in Madrid. The RGF results yielded higher ratios in spring, 0.1–0.13, than in winter and autumn (in the range of 0.02–0.07) when NO2 levels were higher.
Characterization and variability of inorganic aerosols and their gaseous precursors at a suburban site in northern France over one year (2015–2016) Atmos. Environ. (IF 3.708) Pub Date : 2018-11-19 Roger Roig Rodelas, Esperanza Perdrix, Benoît Herbin, Véronique Riffault
Measurements of inorganic precursor gases (NO, NO2, HONO, NH3, SO2 and HCl) and PM2.5 inorganic water-soluble ions (NO3−, SO42−, NH4+, Cl−, Na+, Mg2+, Ca2+, K+) were performed at a suburban site in northern France for the first time using a MARGA 1S with an hourly time-resolution from August 2015 to July 2016. The observations were compared with other independent methods: HR-ToF-AMS, BAM-1020, SO2 and NH3 gas monitors over shorter time periods. The dominant particulate species were NO3−, SO42− and NH4+, with average annual mass contributions to PM2.5 of 28.0%, 13.1% and 9.9%, respectively. The highest concentrations of SIA were found in spring likely due to increased agricultural emissions of precursor gases. A strong formation of ammonium nitrate (NH4NO3) over nighttime was observed for every season and attributed to the condensation of its gaseous precursors NH3 and HNO3. The partitioning of NH4NO3 between the gas and particulate phases was compared with that obtained with the thermodynamic module ISORROPIA II and generally found to agree well except for HNO3. The local or distant origin of each species was determined by means of Non parametric Wind Regression (NWR) polar plots and Potential Source Contribution Function (PSCF) maps. SIA main origins were regional with significant contributions from Belgium, the Netherlands and western Germany. Additionally, several high PM2.5 episodes that lasted more than 2 days were analyzed, showing some common features.
A flexible semi-empirical model for estimating ammonia volatilization from field-applied slurry Atmos. Environ. (IF 3.708) Pub Date : 2018-11-19 Sasha D. Hafner, Andreas Pacholski, Shabtai Bittman, Marco Carozzi, Martin Chantigny, Sophie Génermont, Christoph Häni, Martin N. Hansen, Jan Huijsmans, Thomas Kupper, Tom Misselbrook, Albrecht Neftel, Tavs Nyord, Sven G. Sommer
This work describes a semi-empirical dynamic model for predicting ammonia volatilization from field-applied slurry. Total volatilization is the sum of first-order transfer from two pools: a "fast" pool representing slurry in direct contact with the atmosphere, and a “slow” one representing fractions less available for emission due to infiltration or other processes. This simple structure is sufficient for reproducing the characteristic course of emission over time. Values for parameters that quantify effects of the following predictor variables on partitioning and transfer rates were estimated from a large data set of emission from cattle and pig slurry (490 field plots in 6 countries from the ALFAM2 database): slurry dry matter, application method, application rate, incorporation (shallow or deep), air temperature, wind speed, and rainfall rate. The effects of acidification were estimated using a smaller dataset. Model predictions generally matched the measured course of emission over time in a reserved data subset used for evaluation, although the model over- or under-estimated emission in many individual plots. Mean error was ca. 12% of applied total ammoniacal nitrogen (and as much as 82% of measured emission) for 72 h cumulative emission, and model efficiency (fraction of observed variation explained by the model) was 0.5–0.7. Most of the explanatory power of the model was related to application method. The magnitude and sign of (apparent) model error varied among countries, highlighting the need to understand why measured emission varies among locations. The new model may be a useful tool for predicting fertilizer efficiency of field-applied slurries, assessing emission factors, and quantifying the impact of mitigation. The model can readily be applied or extended, and is available as an R package (ALFAM2, https://github.com/sashahafner/ALFAM2) or a simple spreadsheet (http://www.alfam.dk).
A statistical emulator for multivariate model outputs with missing values Atmos. Environ. (IF 3.708) Pub Date : 2018-11-19 Francesco Finazzi, Yoana Napier, Marian Scott, Alan Hills, Michela Cameletti
Statistical emulators are used to approximate the output of complex physical models when their computational burden limits any sensitivity and uncertainty analysis of model output to variation in the model inputs.In this paper, we introduce a flexible emulator which is able to handle multivariate model outputs and missing values. The emulator is based on a spatial model and the D-STEM software, which is extended to include emulator fitting using the EM algorithm. The missing values handling capabilities of the emulator are exploited to keep the number of model output realisations as low as possible when the computing burden of each realisation is high.As a case study, we emulate the output of the Atmospheric Dispersion Modelling System (ADMS) used by the Scottish Environment Protection Agency (SEPA) to model the air quality of the city of Aberdeen (UK). With the emulator, we study the city air quality under a discrete set of realisations and identify conditions under which, with a given probability, the 40 μgm−3 yearly average concentration limit for NO2 of EU legislation is not exceeded at the locations of the city monitoring stations.The effect of missing values on the emulator estimation and probability of exceedances are studied by means of simulations.
Meteorological conditions for severe foggy haze episodes over north China in 2016–2017 winter Atmos. Environ. (IF 3.708) Pub Date : 2018-11-19 Xin Li, Zhiqiu Gao, Yubin Li, Chloe Y. Gao, Jingzheng Ren, Xiaoye Zhang
This paper aims to identify the meteorological conditions of severe foggy haze events that frequently occurred over North China. We analyzed data collected at 162 ground observation stations operated by China Meteorological Administration (CMA), as well as data from National Centers Environmental Prediction (NCEP) over North China from December 1, 2016 to January 9, 2017. During this period, more than 72% of the regional mean atmospheric visibility was less than 10 km, with a minimum of 1.15 km. The analysis on atmospheric background fields revealed that during the pollution development-maintenance period there were southerlies and lower wind speed in the lower troposphere compared to that during the pollution dissipation period. Slow southerlies transported the southern pollutants to North China, while high pressure system at the 500 hPa level and increasing temperature (caused by air pollutant absorbed radiation) at 850 hPa suppressed the convection and led to pollutants accumulation over the ground. During the pollution dissipation period, there were northerlies and higher wind speed, and the fast northerlies quickly transported the pollutants. The analysis on the dynamic and thermodynamic effect suggests that the smaller horizontal wind vertical shear is attributed to 500 hPa decreased wind speed. The air pollutant warming effect on 850 hPa from absorbed solar radiation and cooling effect on near surface from reduced radiation near surface could lead to a larger correlation between atmospheric visibility and thermodynamic conditions for more than 76%. This coupling structure between air pollutant and thermodynamic situation provide favorable conditions for foggy haze events under air pollutant transport and weak vertical exchange conditions. Therefore, in order to predict foggy haze episodes in North China, we need to better understand its dynamics, especially for decreased middle level wind speed and lower level south flow.
Spatial interpolation of current airborne pollen concentrations where no monitoring exists Atmos. Environ. (IF 3.708) Pub Date : 2018-11-20 Jose Oteros, Karl-Christian Bergmann, Annette Menzel, Athanasios Damialis, Claudia Traidl-Hoffmann, Carsten Schmidt-Weber, Jeroen Buters
BackgroundPollen is naturally emitted and is relevant for health, crop sciences and monitoring climate change, among others. Despite their relevance, pollen is often insufficiently monitored resulting in a lack of data. Thus, spatial modelling of pollen concentrations for unmonitored areas is necessary. The aim of this study was to develop an automatic system for calculating daily pollen concentrations at sites without regular pollen monitoring.MethodWe used data from 14 pollen taxa collected during 2015 at 26 stations distributed across Bavaria, Germany. The proposed system was based on the Kriging interpolation method to spatially model pollen concentrations for unmonitored areas, in combination with regression of environmental parameters. The method also took into account weather effects on daily pollen concentrations.ResultsAn automatic system was developed for calculating current pollen concentrations at any location of the county. The results were displayed as daily pollen concentrations per m3 in maps of 1 km2 resolution. The models are trained automatically for every day by using the pollen and weather inputs. Automatic inputs will increase the usability of the model. In 50% of the cases, Gaussian Kriging was selected as the optimal model. An R2 of 0.5 is reached in external validation without considering the effect of the weather. An R2 of 0.7 is reached after considering the effect of daily weather parameters.ConclusionsA fully automatic pollen network (ePIN) was built in Bavaria during 2018 that delivers data on-line without delay. The proposed method allows for a comparably small number of automatic devices per study area, but still providing information on pollen on any location in the study area.
Episode analysis of regional contributions to tropospheric ozone in Beijing using a regional air quality model Atmos. Environ. (IF 3.708) Pub Date : 2018-11-20 Hailing Liu, Meigen Zhang, Xiao Han, Jialin Li, Lei Chen
Tropospheric ozone (O3) is a major photochemical pollutant during the summer in Beijing and an analysis of its sources and their regional contributions is important in the formulation of O3 control strategies. A typical heavy O3 pollution event occurred in Beijing from July 1 to July 10, 2015. The first two days were defined as clean days with a prevailing northerly wind and low O3 concentrations. The following period from July 3 to July 10 was regarded as polluted days with a prevailing southerly wind and high O3 concentrations. The Integrated Source Apportionment Method (ISAM) implemented in the Regional Atmospheric Modeling System Community Multiscale Air Quality (RAMS-CMAQ) model was applied to quantify the regional contributions to O3 concentrations in Beijing during this pollution episode. The model evaluation shows that the model reproduced the spatiotemporal variations of meteorological conditions (temperature, relative humidity and wind vector) and concentration field (O3 and NO2) well. The diurnal variations of O3 and NOx in both urban and suburban areas are unimodal. The concentration of O3 decreased rapidly in the urban areas after reaching a peak value, but only slowly in the suburbs. The peaks of NOx concentration in suburban areas appear around 05:00 a.m., while those in urban areas appear at 08:00 a.m. With the change in wind direction and enhanced local emissions, the O3 in Beijing was mainly affected by the boundary conditions on clean days and increased by contributions from Tianjin, Hebei, Shandong, and local emissions on polluted days. By contrast, the O3 precursor NO2 was mostly sourced from local and nearby emissions and was only slightly influenced by the meteorological conditions.
Signs of the ozone recovery based on multi sensor reanalysis of total ozone for the period 1979–2017 Atmos. Environ. (IF 3.708) Pub Date : 2018-11-20 Janusz W. Krzyścin, Dariusz B. Baranowski
The total ozone (TO3) multi-sensor reanalysis data-base, on a global scale, is examined for trend variability during the period 1979–2017. A multiple regression model is applied to the seasonal and yearly time series for zonal belts and 2-D bins covering the entire globe. Piecewise linear trend and independent linear trend pattern consisting of three joined and separated lines, respectively, are used to disclose long-term TO3 variability. The first line is for the ozone decline period forced by the increase of ozone depleting substances (ODS) in the stratosphere, the second one stands for an initial recovery phase starting after the ODS overturning at the end of the 1990s, and the third one is for latest trends. Negative trends are estimated outside the tropics in the first segment, especially during spring and summer. Both trend models provide significant year-round declining trend over the entire globe of ∼2% per 10 yr before the ODS overturning. Afterwards, in most cases trends are insignificant. However, significant positive trends are found for some latitudinal bands and bins at least in one of two post-ODS overturning segments. The number of bins with the upward trend is much larger than the number concerning bins with the downward trend. Significant positive year-round trends (∼2–4% per 10 yr) by both models are found over the entire globe, in the tropics, and poleward of 30° parallel after the ODS overturning. All these results support the emergence of ozone recovery on a global scale following the decline in the 1980s and 1990s.
Linking improvements in sulfur dioxide emissions to decreasing sulfate wet deposition by combining satellite and surface observations with trajectory analysis Atmos. Environ. (IF 3.708) Pub Date : 2018-11-17 Nikita Fedkin, Can Li, Russell R. Dickerson, Timothy Canty, Nickolay A. Krotkov
Sulfur dioxide (SO2), a criteria pollutant, and sulfate (SO42−) deposition are major environmental concerns in the eastern U.S. and both have been on the decline for two decades. In this study, we use satellite column SO2 data from the Ozone Monitoring Instrument (OMI), and SO42− wet deposition data from the NADP (National Atmospheric Deposition Program) to investigate the temporal and spatial relationship between trends in SO2 emissions and the downward sulfate wet deposition over the eastern U.S. from 2005 to 2015. To establish the relationship between SO2 emission sources and receptor sites, we conducted a Potential Source Contribution Function (PSCF) analysis using HYSPLIT back trajectories for five selected Air Quality System (AQS) sites - (Hackney, OH, Akron, OH, South Fayette, PA, Wilmington, DE, and Beltsville, MD) - in close proximity to NADP sites with large downward SO42− trends since 2005. Back trajectories were run for three summers (JJA) and three winters (DJF) and used to generate seasonal climatology PSCFs for each site. The OMI SO2 and interpolated NADP sulfate deposition trends were normalized and overlapped with the PSCF, to identify the areas that had the highest contribution to the observed drop. The results suggest that emission reductions along the Ohio River Valley have led to decreases in sulfate deposition in eastern OH and western PA (Hackney, Akron and South Fayette). Farther to the east, emission reductions in southeast PA resulted in improvements in sulfate deposition at Wilmington, DE, while for Beltsville, reductions in both the Ohio River Valley and nearby favorably impacted sulfate deposition. For Beltsville, sources closer than 300 km from the site contribute roughly 56% observed deposition trends in winter, and 82% in summer, reflecting seasonal changes in transport pattern as well as faster oxidation and washout of sulfur in summer. This suggests that emissions and wet deposition are linked through not only the location of sources relative to the observing sites, but also to photochemistry and the weather patterns characteristic to the region, as evidenced by a west to east shift in the contribution between winter and summer. The method developed here is applicable to other regions with significant trends such as China and India, and can be used to estimate the potential benefits of emission reduction in those areas.
Measurements of submicron particles vertical profiles by means of topographic relief in a typical valley city, China Atmos. Environ. (IF 3.708) Pub Date : 2018-11-15 Suping Zhao, Ye Yu, Dahe Qin, Daiying Yin, Zhiheng Du, Jianglin Li, Longxiang Dong, Jianjun He, Ping Li
To reveal PM1 vertical profiles and key affecting factors in a typical urban valley, daytime and nighttime PM1 (the particles with diameters less than 1 μm) samples were collected with medium volume air samplers during 26 December 2017 to 11 January 2018 at five different altitudes by means of high topographic relief at urban areas of Lanzhou. The synchronous boundary layer temperature and humidity profiles were observed by a microwave radiometer. Daytime PM1 concentrations reduced by about 3.86 μg m−3 when the height above the surface increased by 100 m, which was much lower than that for nighttime (5.68 μg m−3 100 m−1) as particles were easily accumulated near the surface when the air was stable during the nighttime. The three typical PM1 vertical profiles were identified by K-means clustering technique. The most frequent cluster with elevated PM1 concentrations near the surface was closely related to temperature inversion around the ground, while the cluster with relatively uniform PM1 within the boundary layer was mainly induced by unstable atmospheric stratification and thus relatively good vertical dispersion. About 50%–60% of PM1 variations could be attributed to atmospheric stratification near the surface in the valley city, which was much higher than that at the hilltop. The PM1 difference increased by 47.14 (36.91) μg m−3 when inversion layer thickness (intensity) increased by 100 m (1 °C 100 m−1). The newly calculated inversion index considering both inversion layer thickness and intensity explained about 87% of PM1 differences between near the surface and at the hilltop. The vertical dispersion had a more significant effect on PM1 than horizontal dispersion near the surface, while PM1 was more largely affected by horizontal dispersion at the hilltop, which was closely related to the valley terrain.
Impacts of ambient temperature, DPF regeneration, and traffic congestion on NOx emissions from a Euro 6-compliant diesel vehicle equipped with an LNT under real-world driving conditions Atmos. Environ. (IF 3.708) Pub Date : 2018-11-15 Jinyoung Ko, Cha-Lee Myung, Simsoo Park
A real driving emissions test procedure was introduced as a supplement to the chassis dynamometer test to diminish the discrepancy between on-road emissions and type approval certification emissions. In this study, on-road NOx emissions from a 2.2 L diesel vehicle equipped with a lean NOx trap were measured not by a portable emissions measurement system but by NOx sensors and an exhaust flow meter. This method provides a strategy for analyzing on-road NOx emissions with a measurement system that is relatively cheap, light and simple. The effects of ambient temperature, diesel particulate filter regeneration, traffic congestion, NOx conversion efficiency and uphill/downhill sections on NOx emissions were evaluated by comparing the NOx emissions characteristics using engine-out and lean NOx trap-out NOx sensors. NOx emissions in congested traffic conditions were 29% higher than those in smooth traffic conditions. NOx emissions at 33 °C were 55% higher than those at 27 °C. Additionally, NOx emissions under specific conditions with diesel particulate filter regeneration were 30% higher than those under normal conditions. The average on-road NOx emission factor for all test cases was 7.35, but this value decreased to 5.7 when an ambient temperature corrective factor (1.6) was applied for extended test conditions.
Real driving particle number (PN) emissions from China-6 compliant PFI and GDI hybrid electrical vehicles Atmos. Environ. (IF 3.708) Pub Date : 2018-11-16 Zhengjun Yang, Yunshan Ge, Daisy Thomas, Xin Wang, Sheng Su, Hu Li, Hongwen He
In this paper, the real driving particle number (PN) emissions from two China-6 compliant hybrid electrical vehicles (HEVs) were measured using a certification-level portable emission measurement system (PEMS) and strict adherence to the regulatory procedures for real driving emission (RDE) testing. The results show that the trip-averaged PN emission factors for the port fuel injection (PFI) HEV and the gasoline direct injection (GDI) HEV were 1.15E+12 and 1.71E+12#/km respectively, much higher than the engine-only counterparts and failing the existing RDE limits. Enriched air-fuel mixtures and probably lowered catalyst conversion efficiencies as a result of more frequent engine stop-and-goes of the HEVs are found to be the underlying reasons for the extra PN emissions. The test results also suggest the necessity to amend the power management strategy currently widely used in HEVs to deal with the PN issue.
Soil ozone deposition: Dependence of soil resistance to soil texture Atmos. Environ. (IF 3.708) Pub Date : 2018-11-16 P. Stella, B. Loubet, C. de Berranger, X. Charrier, E. Ceschia, G. Gerosa, A. Finco, E. Lamaud, D. Serça, C. George, R. Ciuraru
Soil deposition is an essential pathway for tropospheric ozone (O3) removal, but its controlling factors remain unclear. Here, we explored the variability of soil O3 resistance in response to soil texture. To this aim, data of O3 deposition over bare soil obtained from micrometeorological measurements under contrasted meteorological conditions for five sites were used. The results obtained are twofold: (i) soil resistance (Rsoil) increased with soil surface relative humidity (RHsurf), but (ii) this relationship exhibited large site-by-site variability. Further analysis showed that the minimum soil resistance (corresponding to completely dry soil surface or RHsurf = 0%) and the increase of Rsoil with RHsurf are both linked to soil clay content. These results can be explained by (i) the soil surface available for O3 deposition at a microscopic scale which is a function of the soil specific surface area, and (ii) the capacity of a soil to adsorb water according to its clay content and therefore to reduce the surface active for O3 deposition. From these results, a new parameterization has been established to estimate Rsoil as a function of RHsurf and soil clay fraction.
A simplified aerosol retrieval algorithm for Himawari-8 Advanced Himawari Imager over Beijing Atmos. Environ. (IF 3.708) Pub Date : 2018-11-14 Zhaoyang Zhang, Meng Fan, Weiling Wu, Zifeng Wang, Minghui Tao, Jing Wei, Quan Wang
High temporal aerosol optical depth (AOD) is useful for inversing modelling of emissions and for comprehensively understanding the climatology of aerosol. Geostationary satellite has been used to derive AOD over land and ocean. In this study, a novel simplified aerosol retrieval algorithm for Advanced Himawari-8 imager (SARAHI) is developed to retrieve hourly AOD over Beijing from a new-generation geostationary meteorological satellite—Himawari-8, which carries the Advanced Himawari Imager (AHI). The algorithm is based on a simplified radiative transfer model and surface reflectance derived from one-month AHI apparent data. Measurements from AErosol RObotic NETwork (AERONET) sites and JAXA Himawari Monitor Version 2.0 Aerosol Retrieval product (L2ARP2.0) are used to evaluate the performance of AOD retrievals from SARAHI algorithm. There are 73.5%, 78.2%, 74.7% of AOD retrievals falling in the Expected error lines at Beijing_CAMS, Beijing_RADI, and Xianghe sites, respectively. The correlation coefficient is larger than 0.92 with small root mean square error (RMSE) of 0.134–0.164. The retrievals can also reflect the temporal variations of AOD very well. The results indicate that the SARAHI AOD algorithm can derive the regional AOD accurately and is better than the L2ARP2.0 AOD.
Exploring the effects of crop residue burning on local haze pollution in Northeast China using ground and satellite data Atmos. Environ. (IF 3.708) Pub Date : 2018-11-14 Shuai Yin, Xiufeng Wang, Xirui Zhang, Zhongxue Zhang, Yi Xiao, Hiroshi Tani, Zhongyi Sun
In this study, we used ground-measured air pollutants and various remote sensing and meteorological datasets to explore the possible causes of the severe particulate matter (PM) pollution episodes of October and November 2015 in Northeast China. The three pollution episodes in different regions were elaborately characterized by analyzing the time variation of PM2.5 and other pollutants, e.g., CO, NO2, and SO2. The results from MODerate-resolution Imaging Spectrometer (MODIS) revealed that during the study period, dramatic crop residue burning occurred in Northeast China. Combining its time variation and spatial distribution with air pollutants, the crop residue burning was inferred to have a direct influence on the first and second pollution episodes, especially in Heilongjiang Province. Since a cold wave swept Northeast China beginning on 4th November, the PM pollutants were assumed to be transported southward. This assumption was further verified by the backward and forward trajectory models. Additionally, the suddenly increased relative humidity beginning on 7th November and the week of no wind after the cold wave also greatly contributed to the most severe pollution of Liaoning and Jilin on approximately 8th November. Lastly, we compared air quality indexes and pollutants from remote sensing with ground-measured datasets; the results indicated that there were certain correlations and spatial consistency between the two types of datasets, except for UVAI, which is meaningful to the area without an effective ground monitoring network.
Impact of precursor gases and meteorological variables on satellite-estimated near-surface sulfate and nitrate concentrations over the North China Plain Atmos. Environ. (IF 3.708) Pub Date : 2018-11-14 Yidan Si, Shenshen Li, Liangfu Chen, Chao Yu, Hongmei Wang, Yapeng Wang
Previous studies exploring the impact of precursor emissions and meteorological variables on PM2.5 concentrations were typically conducted over a short period and in urban environments. In this analysis, near-surface sulfate and nitrate mass concentrations at a 10-km resolution over the North China Plain (NCP) from 2006 to 2014 were first obtained based on satellite aerosol optical depth (AOD) data and the global 3D chemical transport model (GEOS-Chem) in combination with vertical profiles from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). Using ground-based PM2.5 component concentrations, our satellite-based model yielded correlation coefficients (r) of 0.72 for sulfate and 0.70 for nitrate. Second, the spatiotemporal patterns of the chemical composition and corresponding precursor gases collected from the Ozone Monitoring Instrument (OMI) during the study period were analyzed. The highest levels of nitrate (∼30 μg/m3) and sulfate (∼25 μg/m3) were concentrated in Hebei, Shandong, Henan and Beijing, and the monthly variations of nitrate and NO2 presented a strong correlation coefficient (0.67). Inter-annual changes of nitrate and NO2 exhibited increasing trends of 1.43%/yr and 1.60%/yr, respectively. In contrast, sulfate and SO2 decreased at rates of 3.5%/yr and 0.76%/yr, respectively, and presented a negative correlation (−0.54). Third, the relationships between the components or precursor gases and relative humidity (RH), planetary boundary layer height (PBLH), temperature (TEM) and wind speed (WS) were compared. The results showed that high levels of NO2 were usually accompanied by stable atmospheric conditions (i.e., low TEM, shallow PBLH, low RH and mild WS). Moreover, the nitrate concentration was often dependent on NO2, and they showed similar characteristics with meteorological factors. PBLH and WS had the greatest influence on nitrate concentrations, whereas the effects of RH and WS varied seasonally. Under beneficial conditions, i.e., high TEM, RH and PBLH and low WS, SO2 rapidly converted to sulfate and fluctuated inversely with the sulfate concentration. Overall, high nitrate levels were primarily associated with anthropogenic causes (i.e., extensive emissions), whereas meteorological conditions have a greater effect on the formation of sulfate concentrations than emissions.
Validation of Himawari-8 aerosol optical depth retrievals over China Atmos. Environ. (IF 3.708) Pub Date : 2018-11-13 Zhaoyang Zhang, Weiling Wu, Meng Fan, Minghui Tao, Jing Wei, Jia Jin, Yunhui Tan, Quan Wang
High temporal resolution (every 10 min) aerosol observations are rarely provided by satellite sensors. The Advanced Himawari Imager (AHI) aboard Himawari-8 can provide aerosol optical depth (AOD) over China with this frequency. The sensor provides great opportunity to retrieve the particle matter near the ground and improve air quality modeling using the aerosol products. However, there is still lack of quality validation about AHI AOD. A comprehensive research was conducted to evaluate the performance of AHI aerosol products based on sixteen sun-photometers stations in AErosol RObotic NETwork (AERONET) and Sun–Sky Radiometer Observation Network (SONET) over China. The overall comparison of AHI AOD and ground AOD shows a high correlation (R2 = 0.67). However, there is only 55% of AHI AOD falling in the expected error envelops (±0.05 ± 0.2*AOD ground). AOD bias between AHI AOD and ground AOD increases with the AOD magnitude. The accuracy of AHI AOD is also highly depend on seasons and surface land cover types. Best performance of AHI aerosol retrievals is shown in summer and for urban region. The diurnal variability validation shows that AHI AOD catch the diurnal AOD variations well, especially for summer. Large differences between AHI AOD and MODerate-resolution Imaging Spectrometer (MODIS) aerosol products are shown, especially for northwest China. The analysis indicates that the uncertainties of AHI aerosol retrievals are induced by large errors of aerosol models and surface reflectance estimation in the algorithm.
Ammonia emissions from China-6 compliant gasoline vehicles tested over the WLTC Atmos. Environ. (IF 3.708) Pub Date : 2018-11-13 Xin Wang, Yunshan Ge, Huiming Gong, Zhengjun Yang, Jianwei Tan, Lijun Hao, Sheng Su
Ammonia emissions cause several negative impacts on the quality of air, water and soil, while secondary ammonia formed on three-way catalysts (TWCs) of gasoline vehicles has not been sufficiently investigated, especially in the developing countries. In this paper, tailpipe ammonia emissions from seven China-6 certified, low-mileage gasoline vehicles were measured over the World Harmonized Light-duty Test Cycle (WLTC). The results demonstrated that ammonia emissions from the seven test vehicles ranged from 0.65 ± 0.38 mg/km to 8.01 ± 3.12 mg/km. A comparison with the emission factors reported in other research indicates that these China-6 certified vehicles emitted similar or less ammonia emissions compared to the vehicles certified to older EU and federal regulations. The ammonia emissions from the test vehicles showed very weak linkage with their engine or transmission technologies. For all the test vehicles, the vast majority of ammonia emissions were emitted within the engine warm-up period due to already lighted-off catalysts but still enriched air/fuel mixtures. No ammonia emissions were noticed within any engine-start events. The masses of ammonia-converted ammonium salts were estimated assuming that all the tailpipe ammonia emissions will transform into ammonium nitrate and ammonium sulfate, and compared to the primary PM emissions measured with filters. The masses of salts were drastically higher than the primary PM, which underscored the significance of vehicle-related ammonia emissions as a key ambient PM contributor.
Photochemical degradation of nitrated PAHs in snow Atmos. Environ. (IF 3.708) Pub Date : 2018-11-13 Honghai Xue, Na Zheng, Chunli Kang, Ying Wang, Yuwei Wang
Nitrated polycyclic aromatic hydrocarbons (NPAHs) are derived from PAHs, which are ubiquitous in the aqueous and atmospheric environments, and whose mutagenicity and carcinogenicity are much higher than that of PAHs. Therefore, their environmental transformation has attracted a lot of attention. In the present study, direct and indirect UV photodegradation kinetics of two NPAHs (1-nitropyrene and 1,8-dinitropyrene) in snow were investigated. It was found that the kinetics followed the pseudo-first-order kinetics with the photochemical degradation rate 0.3773 h−1 for 48.98 nM 1-NP and 0.3653 h−1 for 41.00 nM 1,8-DNP. Photosensitizers (hydrogen peroxide and nitrate) promoted the photodegradation of NPAHs. Considering the lower temperature and less microorganisms in snow environment, the photodegradation can be a key factor in determining the fate of NPAHs in sunlit surface snow. To the best of our knowledge, this is the first report on the photodegradation of NPAHs in snow.
Investigation of levoglucosan decay in wood smoke smog-chamber experiments: The importance of aerosol loading, temperature, and vapor wall losses in interpreting results Atmos. Environ. (IF 3.708) Pub Date : 2018-11-14 Vikram Pratap, Qijing Bian, S. Aditya Kiran, Philip K. Hopke, Jeffrey R. Pierce, Shunsuke Nakao
Levoglucosan has been extensively used as a molecular marker of biomass burning in source-apportionment studies over the last few decades. However, recent studies suggest that the atmospheric lifetime of levoglucosan may be in the order of only 1–2 days under summertime conditions relevant to prescribed/wildfires. Implications of levoglucosan reactivity to wintertime conditions, however, remain uncertain despite significant contributions of domestic wood combustion to wintertime air quality. This study presents smog chamber experiments to investigate levoglucosan decay during photo-oxidation of wood smoke over a temperature range between −8 and 10 °C.Significant decay in particle wall-loss corrected levoglucosan is only observed around 10 °C in these experiments. Theoretical analysis shows that the apparent chemical lifetime of levoglucosan increases at lower temperatures as well as at higher organic aerosol mass concentrations as a result of smaller vapor fractions. The chemical lifetime of a molecular marker is commonly interpreted by a relationship between relative decay in particle wall-loss corrected marker concentrations versus integrated OH exposure. However, this relationship strongly depends on vapor wall-loss rates in addition to temperature, organic aerosol concentrations, and OH concentrations. Therefore, inferred lifetimes from a small set of experiments from a single chamber cannot easily be generalized for the full range of atmospheric smoke conditions.
Comparing black and brown carbon absorption from AERONET and surface measurements at wintertime Fresno Atmos. Environ. (IF 3.708) Pub Date : 2018-11-14 Sijie Chen, Lynn Russell, Christopher Cappa, Xiaolu Zhang, Michael Kleeman, Anikender Kumar, Dong Liu, Veerabhadran Ramanathan
The radiative impacts of black carbon (BC) and brown carbon (BrC) are widely recognized but remain highly uncertain. The Aerosol Robotic Network (AERONET) provides measurements of aerosol optical depth (AOD), aerosol absorption optical depth (AAOD), and other parameters. AERONET AAOD measurements have been used to estimate the relative contributions of BC and BrC to the total absorption at select sites and have the potential to be used across the global network, but the accuracy of the partitioning method has not been established and the uncertainties not characterized. We made surface-level measurements of aerosol optical properties from January 13 to February 10, 2013, and from December 25, 2014, to January 13, 2015, at Fresno, California. The contribution of BrC and BC to the absorption at 405 nm was estimated from the surface-level measurements using a combined mass absorption coefficient and thermodenuder method. The surface-level measurements were compared with BC and BrC absorption at 440 nm estimated from AERONET measurements of the absolute AAOD and the absorption Ångstrom exponent (AERONET-AAE method). In 2013, AERONET results showed that BC and BrC contributed 67% and 33%, respectively, of absorption at 440 nm while the surface-level measurements showed that BC and BrC contributed 89% and 11%, respectively, of absorption at 405 nm. In 2014, AERONET results showed BC and BrC absorption were 72% and 28%, respectively, and the BC and BrC surface measurements were 68% and 32%, respectively. The boundary layer conditions showed that the comparison between AERONET measurements and surface-based estimates was more appropriate in 2014 than in 2013. As a result, AERONET measurements and surface-based estimates had strong or moderate correlations and slopes near unity in 2014. Thus, surface measurements were more representative of column BC and BrC absorption in 2014.
Investigation of vehicle cold start primary NO2 emissions from ambient monitoring data in the UK and their implications for urban air quality Atmos. Environ. (IF 3.708) Pub Date : 2018-11-14 Vasileios N. Matthaios, Louisa J. Kramer, Roberto Sommariva, Francis D. Pope, William J. Bloss
Nitrogen oxides (NO and NO2, collectively NOX) derived from vehicle exhausts are critical pollutants with significant implications for urban air quality and human and environmental health. In this study, we investigate trends in measured ambient nitrogen dioxide (NO2) and NOX mixing ratios at urban traffic - dominated monitoring sites in the UK for the period 2009–2016. We apply an oxidant analysis approach alongside a number of assumptions to the ambient data to determine trends in the inferred primary NO2/NOx ratio, and examine evidence for enhanced vehicle “cold start” effects upon these inferred emissions. Ambient NO2 and NOX mixing ratios have experienced an overall decrease of 17.2% and 11.3% respectively for the locations considered over this time period. The inferred primary NO2/NOx ratio for the majority of the study locations is found to have fallen by 29% (from 0.175 to 0.125) as a monthly mean from 2009 to 2016, with a statistically significant median decrease of 0.32 percentage points per year. However, during cold weather (temperatures less than or equal to 5 OC), the inferred primary NO2/NOx ratio averaged across all locations, when compared with normal conditions (temperatures higher than 5 OC) increased from 0.062 (±0.004) to 0.102 (±0.001) (64.5% higher) and from 0.056 (±0.004) to 0.098 (±0.001) (75% higher) for cold morning and evening rush hours, with substantially greater increases at some sites. This “cold start” result suggests that the combination of recent vehicle driving history and ambient weather conditions, in conjunction with technological constraints on the operating temperature range of emission control systems in some vehicles, affects NOx emissions and hence has a detrimental impact upon air quality in urban environments. Increased cold start emissions imply an increased NO2 - derived health burden from air pollution, under certain conditions, assessment of which should consider changes in vehicle use as a result of weather, and hence altered personal exposure.
An accurate and ultrafast method for estimating three-dimensional radiological dose rate fields from arbitrary atmospheric radionuclide distributions Atmos. Environ. (IF 3.708) Pub Date : 2018-11-12 Xinpeng Li, Wei Xiong, Xiaofeng Hu, Sida Sun, Hong Li, Xintuan Yang, Qijie Zhang, Maxime Nibart, Armand Albergel, Sheng Fang
The three-dimensional (3D) distribution of radiological dose rate is important for assessing the biological hazard of atmospheric radionuclides in the environment. Because of the complexity of such scenarios, existing methods only estimate one- or two-dimensional dose rates, and trade accuracy and generality for acceptable speed. The lack of efficient 3D estimation methods prevents the 3D biological effect assessment of atmospheric radionuclides. This paper presents a 3D dose rate field estimation method that accelerates the computation by several orders of magnitude without loss of accuracy or generality. This method reformulates the time-consuming 3D integral in the dose rate model as a convolution and uses a fast Fourier transform to accelerate its solution. The convolution form provides a new receptor-oriented insight into dose rate estimation that can flexibly describe the radiological response of biological tissues. The proposed method makes no approximations or assumptions, so it is accurate and applicable to arbitrary atmospheric dispersion models and radionuclide distributions. Our approach is validated by both simulations and a field experiment. The results show that the proposed method is accurate and fast in both simple and highly complex air dispersion scenarios, and provides better quantitative and qualitative agreement with the experimental data than RIMPUFF's tabulated method. This method bridges the long-standing gap between the refined 3D atmospheric radionuclide transport modelling and the corresponding 3D biological hazard evaluation.
Seasonal and spatial variations of optical properties of light absorbing carbon and its influencing factors in a typical polluted city in Yangtze River Delta, China Atmos. Environ. (IF 3.708) Pub Date : 2018-11-13 Dong Chen, Yu Zhao, Ritao Lyu, Rongrong Wu, Liang Dai, Yi Zhao, Feng Chen, Jie Zhang, Huan Yu, Miao Guan
A major challenge in understanding radiative forcing of aerosols is accurately monitoring the light absorbing components and clarifying the main reasons of their spatial and temporal variations. In this study, the optical properties of light-absorbing carbon (LAC) in aerosols were measured over one year and the impacts from various emission sources and other influencing factors were analyzed at three sites (suburban (NJU), urban (PAES) and industrial (NUIST) in Nanjing, a typical polluted city in eastern China. With an improved method that combines online and offline techniques, we revised the multiple scattering correction factors and significantly reduced the uncertainty in measurement of absorption coefficients of black carbon (BC). The result reveals the necessity of developing the regional dependent factor for estimation of BC absorption. Relatively large mass absorption efficiency (MAE) of BC was found in summer and industrial region (NUIST), and the mixing state and coating relevant with secondary aerosol formation were the main reasons for such seasonal and site dependent variations. Distinct seasonal variations existed in the MAE of brown carbon (BrC) at NJU. In the winter, BrC from primary emissions such as diesel vehicles had a stronger absorption ability than that from secondary aerosol formation. The lowest MAE values of BrC appeared in summer, reflecting the formation of the non-absorbing biogenic secondary organic aerosol, and the effect of photobleaching. At the urban site PAES, BrC was expected to be mainly from gasoline vehicles and transport of biomass burning emissions, and had a stronger light absorbing ability than the other two sites. The results of simultaneous observations at NJU and PAES indicated that the formation of fresh secondary organic aerosol enhanced the optical absorption of BC but reduced that of BrC. The impacts of various influencing factors on LAC provided effective ways to alleviate their regional radiative forcing at the city scale.
Comparing turbulent mixing of atmospheric oxidants across model scales Atmos. Environ. (IF 3.708) Pub Date : 2018-11-13 Yang Li, Mary C. Barth, Allison L. Steiner
Vertical mixing processes as simulated by atmospheric models affect the prediction of vertical profiles of reactive trace gases and oxidants and our understanding of atmospheric chemistry throughout the boundary layer. Specifically, the vertical transport of these oxidants is important for understanding where in situ chemistry occurs. Simulations of the vertical transport are influenced by many factors, including the horizontal and vertical grid resolution, planetary boundary layer (PBL) schemes, and the use of cumulus parameterization to represent sub-grid scale cloud processes. Here, we compare simulations using the Weather Research and Forecasting Model coupled with Chemistry (WRF-Chem) with the NCAR Large Eddy Simulation (LES) model and the NASA P-3B measurements over the Baltimore-Washington region to evaluate the performance of WRF-Chem in simulating vertical mixing of chemical oxidants in the PBL. For two different PBL schemes, WRF-Chem simulates a weaker convective environment and lower PBL height than LES. Comparing WRF simulations, the Yonsei University (YSU) PBL scheme simulates higher and drier PBL than the Mellor-Yamada-Janjic (MYJ) PBL scheme. The stronger vertical mixing in the LES model simulates higher concentrations of chemical oxidants aloft than WRF-Chem, leading to a constant O3 vertical profile up to the top of the LES domain (4.8 km). Weaker vertical mixing in WRF-Chem prohibits upward transport of the key chemical precursors, therefore resulting in low in situ chemical production of O3 and OH aloft in the WRF-Chem simulations with both PBL schemes and reducing the oxidative capacity in the buffer or cloud layer.
Global changes in the diurnal cycle of surface ozone Atmos. Environ. (IF 3.708) Pub Date : 2018-11-13 Sarah A. Strode, Jerald R. Ziemke, Luke D. Oman, Lok N. Lamsal, Mark A. Olsen, Junhua Liu
Changing emissions of NOx and other ozone precursors drive trends in both production and loss of surface ozone, leading to surface ozone trends that differ according to the time of day. Consequently, the magnitude of the diurnal cycle in surface ozone is changing in several regions of the world. Changes in the diurnal cycle of ozone have implications for the metrics used to assess the impact of ozone on human health and vegetation, since different metrics are sensitive to different portions of the diurnal cycle. We use a high resolution model simulation to examine global changes in the magnitude of the diurnal cycle of O3 between 1980 and 2015. The simulation reproduces the negative trends in the tropospheric NO2 column over the eastern United States and Europe, and the positive trends over East Asia, seen by the Ozone Monitoring Instrument (OMI). It also gives a reasonable reproduction of the change in the diurnal cycle of surface ozone seen at rural sites in the eastern United States between the 1990s and 2000s. The simulation shows that the magnitude of the surface O3 diurnal cycle is increasing in regions with positive changes in NOx emissions, such as South and East Asia, and decreasing in regions with reductions in NOx emissions. It also shows changes in the diurnal cycle of the tropospheric ozone column, although these have fewer regions with statistically significant trends. These changes suggest that daily mean ozone is responding less than the mid-day ozone measured by the Total Ozone Mapping Spectrometer (TOMS) and OMI.
The weekday/weekend ozone differences induced by the emissions change during summer and autumn in Guangzhou, China Atmos. Environ. (IF 3.708) Pub Date : 2018-11-13 Y. Zou, C.Q. Yin, E. Charlesworth, X.L. Yan, X.J. Deng, F. Li
Weekday/weekend mixing ratios of ozone (O3) and the O3 precursors of non-methane hydrocarbons (NMHCs) and nitrogen oxides (NOx) were recorded at the Guangzhou Panyu Atmospheric Composition Station (GPACS), a suburban site in Guangzhou, during the summer (June, July, and August) and autumn (September, October, and November) of 2011. In both summer and autumn, weekday/weekend O3 differences in the morning and at midday largely depend on how much the O3 precursors are affected by anthropogenic emissions. In the mornings (6:00–9:00 LT), pollutants (i.e. NOx and NMHCs) were more strongly influenced by vehicular emissions in autumn than in summer. In autumn, O3 titration and lower NOx on weekends in NMHCs-limited regimes lead to more rapid O3 production, which resulted in the O3 weekend effect during autumn morning. No O3 weekend effect occurred on summer mornings because O3 formation was in a NOx-limited regime, although O3 titration still existed. At midday (10:00–16:00 LT), the increase of biogenic NMHCs emissions reversed the sensitivity of O3 production from NMHCs-to NOx-sensitive. The weekday/weekend diurnal pattern of vehicular sources was the same at midday, more intense other human industrial activities in autumn not only gave rise to the higher mixing ratios of high-reactive anthropogenic NMHCs (e.g. aromatics) on weekdays, but also could affected the temperature in the city, leading to higher isoprene mixing ratio on weekdays. All these factors are likely to contribute to the O3 weekday effect in autumn. Meanwhile no weekday O3 effect occurred in summer due to the low-intensity industrial anthropogenic activities. Our results show that high-reactive NMHCs and NOx control can be effective for reducing peak O3 mixing ratios in Guangzhou. Further investigation based on numerical models is required to reach more robust conclusions.
Multi-isotope approach of Pb, Cu and Zn in urban aerosols and anthropogenic sources improves tracing of the atmospheric pollutant sources in megacities Atmos. Environ. (IF 3.708) Pub Date : 2018-11-10 C.E. Souto-oliveira, M. Babinski, D.F. Araújo, D.J. Weiss, I.R. Ruiz
Studies including multiple isotope systems in aerosols promises unparalleled insights into sources and pathways of metals in the atmosphere. However, such studies remain rare because of the challenges associated with small sample sizes and low analyte masses of the target elements. Here, we present the first study combining accurate and precise determination of Pb, Cu and Zn isotopic ratios in aerosols and anthropogenic materials collected in São Paulo, Brazil. We use a sequential ion chromatography procedure with two different resins for the separation and purification of the analytes. Multi collector mass spectrometry is used for the accurate and precise determination of the isotope ratios. Long term analytical reproducibilities are ±0.035 for 206Pb/204Pb, ± 0.13‰ for δ65CuNIST and ±0.1‰ for δ66ZnJMC (±2σ). Accuracy is assessed using certified reference materials (CRM NIST 2783 aerossol, BRP-1 and others). We analyzed 57 source samples (road dust, tires, cement, road tunnel aerosol) and 113 aerosol samples collected between 2013 and 2015. The results for São Paulo are critically compared with previously published data from studies conducted in São Paulo, London and Barcelona. The key findings are: 1. The isotope signatures for Zn in tires (δ66ZnJMC = 0.16 ± 0.14, 2σ, n = 9) and road dust (δ66ZnJMC = 0.17 ± 0.19, 2σ, n = 13) are similar in São Paulo and London suggesting that this isotope system can be used as element specific tracers for non-exhaust traffic. 2. 206Pb/207Pb vs δ66ZnJMC and δ66ZnJMC vs δ65CuNIST multi-isotopic diagrams successfully separate wear off from cars including tires and brakes, car exhaust, industrial emissions and cement sources and improves the discrimination of air pollutant sources. 3. The source identification based on isotope ratios agrees source apportionement based on emissions inventory from these cities. 4. We present Pb, Cu and Zn isotopic data for the first time for the CRM NIST 2783 and BRP-1. These new data will enable future intercalibration and quality controls in other laboratories. Our study confirms that stable isotope ratio analysis have a great potential for element specific source characterization (e.g., separating non combustion traffic sources from combustion sources) for Cu, Zn and Pb.
Isolation and radiocarbon analysis of elemental carbon in atmospheric aerosols using hydropyrolysis Atmos. Environ. (IF 3.708) Pub Date : 2018-11-10 Xiangyun Zhang, Jun Li, Yangzhi Mo, Chengde Shen, Ping Ding, Ning Wang, Sanyuan Zhu, Zhineng Cheng, Jiazhuo He, Yankuan Tian, Shutao Gao, Qin Zhou, Chongguo Tian, Yingjun Chen, Gan Zhang
Radiocarbon (14C) analysis is a powerful tool that can unambiguously distinguish fossil and non-fossil sources of carbonaceous particles. However, one of the big challenges of this method is to isolate elemental carbon (EC) or black carbon (BC) for 14C analysis. Hydropyrolysis (hypy) has proven to be an effective method for separating BC in environmental matrices. The potential of hypy for isolation of EC from atmospheric aerosols is evaluated using typical combustion products from non-fossil (biomass), fossil fuel (coal and petroleum), and ambient aerosol samples collected in Beijing and Guangzhou. Using solid state nuclear magnetic resonance (NMR) along with measurement of carbon content and 14C, hypy conditions of 15 MPa hydrogen pressure and 550 °C temperature was confirmed to effectively separate EC from aerosol samples. Consequently, a comparison study of EC 14C in aerosol samples separated using the two-step heating method (CTO-375), thermal-optical method and hypy was conducted. The results show that hypy is an effective and stable approach for matrix-independent 14C quantification of EC in aerosols.
Predicting the spatial distribution of emissions from urban buses based on previously measured data and scenarios for their modernization in the future. Case study: Krakow, Poland Atmos. Environ. (IF 3.708) Pub Date : 2018-11-11 Marek Bogacki, Paulina Bździuch
This paper presents the results of research on the impact of various projected scenarios for urban bus transportation modernization in Krakow, in regards to air emissions. The research was carried out on the fleet of urban buses operating within the Krakow metropolitan area. The levels and amounts of the 16 substances were evaluated using the CORINAIR methodology. The scenarios were determined based on the data measured between 2010 and 2015 and according to the plans created by Krakow's carriers. An analysis of the plans for the urban bus fleet modernization in Krakow shows that it will have a positive influence on the reduction in particulate matter and gas emissions into the air. The implementation of the projected scenarios, which involves the replacement of old buses with modern, low or zero emission vehicles, will reduce the emission of nitrogen oxides (NOx) by more than 60%, volatile organic compounds (VOCs) by more than 82%, carbon monoxide (CO) by nearly 52%, and particulate matter from fuel combustion (PMex) by more than 77% by 2025. Research also shows an increase N2O emissions (by almost 43%) as a result of modernization. This phenomenon is characteristic for modern engines. Moreover, introducing electric buses into a fleet contributes to the gradual reduction of benzo(a)pyrene emissions. Even though the replacement of a bus fleet is a long-term and costly process, taking such action for Krakow and the neighboring municipalities is essential to improving the air quality in that area, especially in terms of excessive concentrations of particulate matter and nitrogen oxides.
Seasonal characteristics of particulate polycyclic aromatic hydrocarbons (PAHs) in a petrochemical and oil refinery industrial area on the west coast of South Korea Atmos. Environ. (IF 3.708) Pub Date : 2018-11-11 Phan Quang Thang, Seong-Joon Kim, Sang-Jin Lee, Jin Ye, Young-Kyo Seo, Sung-Ok Baek, Sung-Deuk Choi
The Daesan industrial complex is one of the largest petrochemical and oil refinery industrial complexes in South Korea, which is believed to be a major source of polycyclic aromatic hydrocarbons (PAHs). Total suspended particle (TSP) samples (n = 84) were seasonally collected at two industrial sites and one residential site, and 19 PAHs were analyzed. Concentrations of individual PAHs ranged from 0.01 to 2.52 ng/m3, and annual mean concentrations of Σ19 PAHs at Sites 1, 2, and 3 were 5.88, 4.52, and 5.08 ng/m3, respectively. The concentrations of Σ19 PAHs in warm seasons (spring and summer) were lower than those in cold seasons (autumn and winter). Annual fractions of low molecular weight (LMW)-PAHs (2–3 rings, 12.1%) and high molecular weight (HMW)-PAHs (4–7 rings, 87.9%) indicated a strong contribution of thermal processes. Significant correlations between Σ19 PAHs and TSP (p < 0.01) at all the sampling sites were observed, implying that increased TSP levels were responsible for elevated levels of PAHs. There were strong seasonal variations in the profiles of PAHs, and they were clearly reflected in the results of the principal component analysis. Diagnostic ratios and backward air trajectories suggested seasonal variations in the contribution of local emissions and long-range transport. The diagnostic ratios suggested that mixed sources were dominant in cold seasons, while coal/biomass burning and non-traffic sources were prevailing in warm seasons. BeP/BaP ratios indicated that local emissions were major sources compared with long-range transport except for summer. Backward air trajectories in winter suggested the influence of long-range transport, but local emissions were more important in this study area.
Formation of oxidized organic compounds from Cl-initiated oxidation of toluene Atmos. Environ. (IF 3.708) Pub Date : 2018-11-12 Surya Venkatesh Dhulipala, Sahil Bhandari, Lea Hildebrandt Ruiz
The formation of secondary organic aerosol (SOA) from toluene can impact urban air quality and therefore human health. Most SOA studies have focused on OH chemistry; however recent work suggests that chlorine atoms (Cl) may affect tropospheric chemistry more than previously assumed. This work focuses on SOA formation from Cl-initiated oxidation of toluene under different conditions. The fast reaction between Cl and toluene enabled complete consumption of toluene in environmental chamber experiments and aging of the toluene SOA. A high resolution time-of-flight chemical ionization mass spectrometer was used to observe several generations of gas-phase products. The presence of nitric oxides (NOx) appears to delay the formation of later generation products. Data from an aerosol chemical speciation monitor suggest that all SOA formed had high oxidation state, and that the bulk organic composition was different for SOA from Cl-dominated reactions compared to SOA from OH-dominated reactions. Addition of oxidant after all toluene had been consumed did not result in a significant change in the organic aerosol oxidation state, suggesting that the system may have reached an oxidative end-point in the particle phase.
A new method for assessing the efficacy of emission control strategies Atmos. Environ. (IF 3.708) Pub Date : 2018-11-09 Huiying Luo, Marina Astitha, Christian Hogrefe, Rohit Mathur, S. Trivikrama Rao
Regional-scale air quality models and observations at routine air quality monitoring sites are used to determine attainment/non-attainment of the ozone air quality standard in the United States. In current regulatory applications, a regional-scale air quality model is applied for a base year and a future year with reduced emissions using the same meteorological conditions as those in the base year. Because of the stochastic nature of the atmosphere, the same meteorological conditions would not prevail in the future year. Therefore, we use multi-decadal observations to develop a new method for estimating the confidence bounds for the future ozone design value (based on the 4th highest value in the daily maximum 8-hr ozone concentration time series, DM8HR) for each emission loading scenario along with the probability of the design value exceeding a given ozone threshold concentration at all monitoring sites in the contiguous United States. To this end, we spectrally decompose the observed DM8HR ozone time series covering the period from 1981 to 2014 using the Kolmogorov-Zurbenko (KZ) filter and examine the variability in the relative strengths of the short-term variations (induced by synoptic-scale weather fluctuations; referred to as synoptic component, SY) and the long-term component (dictated by changes in emissions, seasonality and other slow-changing processes such as climate change; referred to as baseline component, BL). Results indicate that combining the projected change in the ozone baseline level with the adjusted synoptic forcing in historical ozone observations enables us to provide a probabilistic assessment of the efficacy of a selected emissions control strategy in complying with the ozone standard in future years. In addition, attainment demonstration is illustrated with a real-world application of the proposed methodology by using air quality model simulations, thereby helping build confidence in the use of regional-scale air quality models for supporting regulatory policies.
Effect of short-chain alcohols on the bulk-phase reaction between glyoxal and ammonium sulfate Atmos. Environ. (IF 3.708) Pub Date : 2018-11-10 Andrew E. Berke, Tara A. Bhat, Hunter Myers, Emma F. Gubbins, Amanda A.O. Nwankwo, Kim Lu, Lily Timpane, Claire Keller
The chemical and physical properties of secondary organic aerosol (SOA) may be influenced by the aqueous environment within which SOA-forming reactions occur. Bulk-phase reactions between glyoxal and ammonium sulfate produce light-absorbing compounds such as imidazole-2-carboxaldehyde (IC) and biimidazole (BI) and model aerosol-phase chemistry. The effect of solvent composition on IC and BI production kinetics were examined for solutions containing a series of short-chain alcohols (methanol, ethanol, 1-propanol, 2-propanol, 2-butanol, tert-butanol, and 3-methyl-2-butanol), as functions of the species and concentration added. The addition of an alcohol likely altered the solvent by inducing the formation of micro-heterogeneities of hydrated alcohol molecules. An increased alcohol concentration in solution resulted in a general increase in the production of IC and BI, with ethanol and the secondary alcohols causing the largest changes. The rate constants for IC and BI production in solutions that do not contain alcohol are found to be (4.03 ± 2.02) x 10−6 s−1 and (3.48 ± 1.75) x 10−6 s−1, respectively. In solutions that do contain an alcohol, rate constant values range from 3.23 × 10−6 s−1 to 6.61 × 10−6 s−1 for IC and 0.985 × 10−6 s−1 to 6.87 × 10−6 s−1 for BI, depending on the alcohol and the concentration. While these prevailing trends of more alcohol in solution leading to amplified production of imidazoles were observed for all seven alcohols, the diversity of responses implies the mode of action depends strongly on the species of alcohol added. Properties that describe a solution in bulk, such as dielectric constant, are not found to be reliable predictors of subsequent system behavior. Solvent composition influences SOA chemistry, and interactions between relevant functional groups within solution drive this influence, which suggests the importance of understanding individual relationships between aerosol-phase chemicals and SOA properties and production.
Investigating sources of variability and error in simulations of carbon dioxide in an urban region Atmos. Environ. (IF 3.708) Pub Date : 2018-11-10 Cory R. Martin, N. Zeng, A. Karion, K. Mueller, S. Ghosh, I. Lopez-Coto, K.R. Gurney, T. Oda, K. Prasad, Y. Liu, R.R. Dickerson, J. Whetstone
As cities embark upon greenhouse gas (GHG) mitigation efforts, there is an increasing need for accurate quantification of urban emissions. In urban areas, transport and dispersion is particularly difficult to simulate using current mesoscale meteorological models due, in part, to added complexity from surface heterogeneity and fine spatial/temporal scales. It is generally assumed that the errors in GHG estimation methods in urban areas are dominated by errors in transport and dispersion. Other significant errors include, but are not limited to, those from assumed emissions magnitude and spatial distribution. To assess the predictability of simulated trace gas mole fractions in urban observing systems using a numerical weather prediction model, we employ an Eulerian model that combines traditional meteorological variables with multiple passive tracers of atmospheric carbon dioxide (CO2) from anthropogenic inventories and a biospheric model. The predictability of the Eulerian model is assessed by comparing simulated atmospheric CO2 mole fractions to observations from four in situ tower sites (three urban and one rural) in the Washington DC/Baltimore, MD area for February 2016. Four different gridded fossil fuel emissions inventories along with a biospheric flux model are used to create an ensemble of simulated atmospheric CO2 observations within the model. These ensembles help to evaluate whether the modeled observations are impacted more by the underlying emissions or transport. The spread of modeled observations using the four emission fields indicates the model's ability to distinguish between the different inventories under various meteorological conditions. Overall, the Eulerian model performs well; simulated and observed average CO2 mole fractions agree within 1% when averaged at the three urban sites across the month. However, there can be differences greater than 10% at any given hour, which are attributed to complex meteorological conditions rather than differences in the inventories themselves. On average, the mean absolute error of the simulated compared to actual observations is generally twice as large as the standard deviation of the modeled mole fractions across the four emission inventories. This result supports the assumption, in urban domains, that the predicted mole fraction error relative to observations is dominated by errors in model meteorology rather than errors in the underlying fluxes in winter months. As such, minimizing errors associated with atmospheric transport and dispersion may help improve the performance of GHG estimation models more so than improving flux priors in the winter months. We also find that the errors associated with atmospheric transport in urban domains are not restricted to certain times of day. This suggests that atmospheric inversions should use CO2 observations that have been filtered using meteorological observations rather than assuming that meteorological modeling is most accurate at certain times of day (such as using only mid-afternoon observations).
Source apportionment using receptor model based on aerosol mass spectra and 1 h resolution chemical dataset in Tianjin, China Atmos. Environ. (IF 3.708) Pub Date : 2018-11-10 Xing Peng, Xiaoxi Liu, Xu-Rong Shi, Guo-Liang Shi, Mei Li, Jia-Yuan Liu, Yan-Qi Huangfu, Hong Xu, Ruo-Yu Ma, Wei Wang, Yin-Chang Feng
Source apportionment studies have been performed on online receptor datasets in recent years (called online source apportionment), including mass spectra and online chemical dataset. Single particle aerosol mass spectrometry (SPAMS), an important online technique, has the ability to analyze mass spectrum (MS) and particular size information of a single particle in real time. Clustering methods have been widely applied to MS dataset to investigate the sources of particles, although the receptor models are the common tools to probe the particle sources based on the receptor dataset. This work developed a new method (SPAMS-RM) that employed the receptor model (RM) on an MS dataset from SPAMS to identify particle sources. Particles were measured by SPAMS from July 14 to August 15, 2015, at an urban site in Tianjin, China. Multilinear Engine-2 (ME2) and adaptive resonance theory-based neural networks-2a (ART-2a) were separately used to analyze the single particle MS dataset. This work also evaluated the performance of SPAMS-RM method. Concentrations of chemical components of PM2.5 (particulate matter with an aerodynamic diameter of less than 2.5 μm) and gaseous pollutants were measured by independent online instruments (1 h resolution). Source apportionment was separately conducted using two receptor models, Positive Matrix Factorization (PMF) and ME2, based on the 1 h resolution chemical dataset. This method was called online chemical source apportionment (OCSA-RM). ART-2a obtained 19 clusters that merged into five major classes: carbon species, rich-K, sea salt, crustal dust, and industrial metals. SPAMS-RM identified eight sources by interpreting the MS characteristic of factors and investigating the relationship of the temporal trends of factor contributions, chemical species, gaseous pollutants, and particle clusters. OCSA-ME2 and OCSA-PMF both identified seven factors. Source apportionment results between SPAMS-RM and OCSA-ME2/PMF were compared. Each method identified coal combustion, biomass burning, sea salt, nitrate source, sulfate source, vehicle emission, and crustal dust. The SPAMS-RM results showed that nitrate source was the most significant contributor (34%) to the PM followed by sulfate source (17%), coal combustion (14%), crustal dust (11%), vehicle emission (10%), biomass burning-OCEC (7%), and industrial activities & sea salt (4%). Some differences between SPAMS-RM and OCSA-ME2/PMF results existed and might be due to chemical analysis methods and sampling methods. ME2 was used for the first time to identify the PM sources based on the MS dataset from SPAMS and demonstrated its capability when coupled with MS dataset from SPAMS to apportion the source of PM.
Factor analysis of chemical ionization experiments: Numerical simulations and an experimental case study of the ozonolysis of α-pinene using a PTR-ToF-MS Atmos. Environ. (IF 3.708) Pub Date : 2018-11-10 Bernadette Rosati, Ricky Teiwes, Kasper Kristensen, Rossana Bossi, Henrik Skov, Marianne Glasius, Henrik B. Pedersen, Merete Bilde
In this study we examine the application of a factor analysis technique for datasets recorded by the chemical ionization instrument Proton Transfer Reaction - Time-of-Flight - Mass Spectrometer (PTR-ToF-MS). Numerical simulations were carried out to test and optimize the performance of the factorization method Multivariate Curve Resolution - Alternating Least Squares (MCR-ALS). The simulations demonstrated that the choice of initial estimates for the factor analysis are crucial for the outcome of the factorization. For this purpose we describe a new method based on the Pearson correlation coefficient which, compared to the other tested methods, yields the best factorization results. Overlapping contributions of different substances to a certain mass bin and large uncertainties in the data deteriorate the performance of the factor analysis. The deconvolution technique was also applied to data obtained with a PTR-ToF-MS employed at a smog chamber. The response from single substances (fragmentation patterns) such as α-pinene, α-pinene oxide and pinonaldehyde as well as a more complex experiment involving the ozonolysis of α-pinene are investigated. For the single substances, the factorization method points to the presence of impurities which could be differentiated from the masses affiliated with the actual substances. The α-pinene ozonolysis experiment was analysed with the factorization technique and yielded four factors, one representing the decay of the reactant and three different products. The matrix factorization technique appeared to be a valuable tool allowing for a detailed analysis of complex mass spectra without the need of any prior information.
Decreasing trend of elemental carbon concentration with changes in major sources at Mega city Nagoya, Central Japan Atmos. Environ. (IF 3.708) Pub Date : 2018-11-10 Makiko Yamagami, Fumikazu Ikemori, Hironori Nakashima, Kunihiro Hisatsune, Kazuo Osada
The atmospheric concentration of elemental carbon (EC) in aerosol particles is a key parameter related to global warming and health effects. Emission regulations for diesel exhaust intended to reduce EC concentrations have been strengthened in recent years. To investigate regulation effects in Japan, daily EC concentrations in the megacity of Nagoya, central Japan, were measured during April 2003–March 2016. The EC concentrations showed a decreasing trend with changing seasonal variation: high concentrations were found in autumn and winter before 2011, but no seasonal variation was discernible after 2012. Strong correlation was found for annual vehicular EC emissions and annual mean EC concentrations during 2003–2009. However, the relation after 2010 was weaker in spring and summer. Based on the relation of EC with trace element (Pb, V, Sb, etc.) concentrations and the backward air trajectories on high concentration days, EC sources other than vehicles were found to be related to long-range transport of air pollution from China in spring and combustion of heavy oil, including ship engine exhaust, in summer.
Flaring emissions in Africa: Distribution, evolution and comparison with current inventories Atmos. Environ. (IF 3.708) Pub Date : 2018-11-10 Thierno Doumbia, Catherine Liousse, Sekou Keita, Louise Granier, Claire Granier, Christopher D. Elvidge, Nellie Elguindi, Kathy Law
Flaring emissions are a major concern due to large uncertainties in the amount of chemical compounds released into the atmosphere and their evolution with time. A methodology based on DMSP (Defense Meteorological Satellite Program) nighttime light data combined with regional gas flaring volumes from National Oceanic and Atmospheric Administration's National Centers for Environmental Information (NOAA-NCEI) has been developed to estimate flaring emissions. This method is validated in Nigeria where individual field company data are available. The spatial distribution of CO2, CH4, NMVOCs, CO, OC, BC, SO2 and NOx is derived for the African continent for the period 1995–2010.A range of the emissions due to flaring is estimated based on the range of emission factors (EFs) for each chemical species. An average decrease in CO2 emissions of about 30% is found over Africa from 1995 to 2010, with Nigeria being the largest contributor to this reduction (up to 50%). Changes in the spatial distribution with time indicate local increases, particularly at offshore platforms, which are attributed to a lack of regulations as well as aging infrastructures in oil and gas fields.Comparisons with current inventories reveal differences in the location and magnitude of point source emissions. For chemical compounds such as NMVOCs and CH4, the ECLIPSE and EDGAR country-level values are considerably higher than the highest flaring emission estimated in this study for 2005. For species such as CO, OC, BC, SO2 and NOx, the emissions provided by the ECLIPSE and EDGAR inventories are generally within the same order of magnitude as the average values found in this study, with the exception of OC, BC and SO2 in which EDGAR provides much lower emissions. These discrepancies are likely due to either differences in the methodologies used to estimate the emissions, in the values of the emission factors considered, or in the definition of flaring sector. Our current estimations suggest that BC, CH4 and CO2 flaring emissions in Africa account for 1–15% (on average 7%), 0.5–8% (on average 2%) and 8–13% (on average 11%) of African total anthropogenic emissions, respectively. The contribution of flaring to African anthropogenic emissions varies widely among countries. For example, in Nigeria the average emissions due to flaring are estimated to be as high as 18% for BC, 10% for CH4 and 50% for CO2, which is significantly greater than the continental average and highlights the importance of emissions in flaring areas.
Atmospheric mercury emissions from two pre-calciner cement plants in Southwest China Atmos. Environ. (IF 3.708) Pub Date : 2018-11-10 Xinyu Li, Zhonggen Li, Tingting Wu, Ji Chen, Chengcheng Fu, Leiming Zhang, Xinbin Feng, Xuewu Fu, Li Tang, Zhikang Wang, Zhibo Wang
Evaluating near-roadway concentrations of diesel-related air pollution using RLINE Atmos. Environ. (IF 3.708) Pub Date : 2018-11-10 Regan F. Patterson, Robert A. Harley
The near-roadway pollutant dispersion model RLINE was evaluated for prediction of nitrogen oxides (NOx) and black carbon (BC) concentrations. Model predictions were compared with continuous, yearlong measurements from two near-roadway sites in the San Francisco Bay Area. Heavy-duty diesel trucks were a significant source of NOxand BC at both sites. Characterization of temporal variations in heavy-duty truck activity on diurnal, weekly, and seasonal scales were included in this study; truck traffic and emissions are not well-correlated with passenger vehicle or total traffic volumes. For both pollutants, more than 90% of predicted 24-h average concentrations were within a factor of two of observations at both near-roadway monitoring sites. The model responds appropriately to seasonal variations in meteorology and day-of-week variations in emissions. RLINE model performance for NOxwas better overall than for BC. Reducing uncertainties in emission factors would help to improve model performance for BC.
Interannual variation of air quality across an international airshed in Detroit (USA) and Windsor (Canada): A comparison of two sampling campaigns in both cities Atmos. Environ. (IF 3.708) Pub Date : 2018-11-09 Lindsay Miller, Xiaohong Xu, Lawrence D. Lemke, Amanda J. Wheeler
This study investigates air pollutant concentrations across the international airshed spanning Detroit, Michigan, USA and Windsor, Ontario, Canada. The Geospatial Determinants of Health Outcomes Consortium (GeoDHOC) measured air quality concurrently in Detroit and Windsor using consistent sampling methods and locations during separate, two-week periods in September 2008 and May/June 2009. This paper presents 2009 results and compares them to previously reported 2008 campaign results to assess spatial and temporal variability. A high-density array of 100 passive and 50 active samplers was used to measure nitrogen dioxide (NO2), 26 volatile organic compounds (VOCs), 23 polycyclic aromatic hydrocarbons (PAHs), and three size fractions of particulate matter (PM) in both campaigns. Geospatial and non-spatial tools were used to investigate changes in concentration distributions and site classification into low/medium/high tertiles between the campaigns. During the two-week 2009 campaign, general pollution patterns remained consistent with those observed during 2008. Higher concentrations in Detroit, strong correlations amongst the BTEX group, and consistency of sites falling into the low and high tertiles were observed. Similar spatial patterns for NO2, VOCs, BTEX, and PAHs were also found during both campaigns. Conversely, PM1-2.5 and PM2.5-10 distributions showed greater variability, as did toluene/benzene ratios. Observed differences are attributable to changes in point source emissions associated with changes in localized activities, possibly related to decreased economic and industrial activity in response to the downturn that began in late 2008. Repeated sampling at multiple locations is important to determine spatial and temporal variability in absolute concentrations. However, if the definition of relatively high and low concentrations regions within a well-established urban area is adequate to estimate future air pollutant exposures, a single multi-location campaign may suffice.
Uncertainties in O3 concentrations simulated by CMAQ over Japan using four chemical mechanisms Atmos. Environ. (IF 3.708) Pub Date : 2018-11-08 Kyo Kitayama, Yu Morino, Kazuyo Yamaji, Satoru Chatani
Uncertainty was evaluated in four chemical mechanisms pertaining to O3 concentrations predicted over Japan by the Community Multiscale Air Quality Model (CMAQ) to investigate factors contributing to model overestimation of O3 concentration. The model setting and meteorological and emissions input data were obtained from a Japanese model inter-comparison project, Japan's Study for Reference Air Quality Modeling (J-STREAM). The compared gas-phase chemical mechanisms included the Carbon Bond Mechanism (CB05TUCL), Regional Atmospheric Chemical Mechanism (RACM2), and two mechanisms developed by the State Air Pollution Research Center (SAPRC), namely SAPRC07TC and SAPRC99. The O3 concentrations produced by CB05TUCL were low compared to those from SAPRC07TC. The RACM2 concentrations were similar to those from SAPRC07TC over inland Japan and lower over the sea. The concentrations from SAPRC99 were higher than those from SAPRC07TC in urban areas and lower in other areas. At most of the monitoring sites in Japan, the modeled O3 concentrations were higher than those from observations. Module overestimation can be ranked in the order of SAPRC99 > SAPRC07TC > RACM2 > CB05TUCL for urban sites and SAPRC07TC > SAPRC99 > RACM2 > CB05TUCL for rural sites. The concentration differences between the chemical mechanisms were within 10 ppb, whereas those between the observed and simulated O3 concentrations reached 40 ppb. Differences in O3 concentrations between the chemical mechanisms accounted for only a part of the model overestimation, while the rest remained unexplained. To investigate factors influencing the differences in O3 concentration between the chemical mechanisms, domain- and 10-vertical-layer-average hourly integrated process rates (IPRs) and integrated reaction rates (IRRs) were calculated using process analysis in CMAQ. The O3 chemical IPRs from SAPRC07TC were higher than those from CB05TUCL and RACM2. The SAPRC99 IPRs were higher than those from SAPRC07TC in urban areas and lower in other areas. The IRR differences in the chemical mechanisms showed that IRRs for the O3 and NO reactions were responsible for the differences in the O3 chemical IPR. The coefficients of determination between the O3 chemical process IPR and IRR differences in the chemical mechanisms were highest for the HO2-NO reaction in CB05TUCL and SAPRC99 and the RO2-NO reaction in RACM2. Differences in reaction rate constants and lumped volatile organic compounds may have caused some of the differences in O3 production between the chemical mechanisms.
High-fidelity simulations of Chemical Plume Tracing in the planetary boundary layer Atmos. Environ. (IF 3.708) Pub Date : 2018-11-05 Alon Manor, Sharon Marx, Ran Aharoni
The localization of a source emitting gas to the outdoor atmosphere has many applications for air quality monitoring and chemical hazard mitigation. Chemical Plume Tracing (CPT) refers to the utilization of autonomous robotic platforms equipped with chemical and anemometry sensors to preform this task. Numerical simulations are an important tool in the development of CPT algorithms. Here, for the first time, high fidelity environmental simulations of the Atmospheric Boundary Layer (ABL) are utilized for the study of CPT algorithm. Large Eddy Simulation (LES) modeling using the PALM model is applied for producing high-resolution three-dimensional flow and dispersion simulations of the outdoor ABL. A CPT bio-inspired algorithm is simulated on top of the modeled environment. Multiple tests are conducted, following statistical analysis of the overall performance. The advantage of the suggested modeling framework over former used methods is exemplified through the study of two issues. First, a theoretical optimal velocity of the robotic platform is quantitatively estimated. Secondly, based on the three-dimensional nature of LES modeling, an extension of the CPT algorithm, aimed for the localization of elevated sources, is presented and tested. The comparison of CPT performance for elevated versus ground sources reveals the considerable difficulty involved in tracing an elevated plume.
The effects of simulating volcanic aerosol radiative feedbacks with WRF-Chem during the Eyjafjallajökull eruption, April and May 2010 Atmos. Environ. (IF 3.708) Pub Date : 2018-11-02 Marcus Hirtl, Martin Stuefer, Delia Arnold, Georg Grell, Christian Maurer, Stefano Natali, Barbara Scherllin-Pirscher, Peter Webley
Explosive volcanic eruptions can inject large amounts of ash and gases into the atmosphere. Such volcanic aerosols can have a significant impact on the surrounding environment, and there is the need to closely investigate their effects on meteorology on local, regional, and even continental scale. This work presents a study of the 2010 Eyjafjallajökull volcanic eruption the resulting ash dispersion and its radiative feedback effects on the meteorological conditions with the Weather Research Forecasting model with on-line Chemistry (WRF-Chem). Two model runs, one meteorology-only simulation (without chemistry) and one that considers gas- and aerosol chemistry as well as direct- and semidirect aerosol feedbacks were performed and compared. Results for daily values show that aerosol radiative feedback effects can cool the atmosphere close to the surface on average by 1 °C with maximum cooling exceeding even 2 °C for the considered episode. Near-surface atmospheric wind speed changed on average by 0.5 m/s with maximum values above 2 m/s. Furthermore, the presence of ash aerosols affected the vertical shape of the profiles of wind speed and temperature and resulted in a better agreement with radiosonde measurements when radiative feedback effects were considered. Although the modeling of the dispersion of volcanic ash clouds is subject to large uncertainties, we have demonstrated that the WRF-Chem model can reproduce observations at surface levels and vertical profiles more realistically when radiative feedback effects are considered in the simulations.
High-resolution simulation of wintertime fossil fuel CO2 in Beijing, China: Characteristics, sources, and regional transport Atmos. Environ. (IF 3.708) Pub Date : 2018-11-02 Tian Feng, Weijian Zhou, Shugang Wu, Zhenchuan Niu, Peng Cheng, Xiaohu Xiong, Guohui Li
In this study, a high-resolution simulation of fossil fuel CO2 in Beijing and surrounding areas, China, during January 2014 is performed to investigate the characteristics and sources of Beijing fossil fuel CO2 (FFCO2) mixing ratios and the impact of regional transport. The model reasonably reproduces the observed meteorological fields in the study domain, including temperature, relative humidity, wind speed, and wind direction. The simulated CO2 and CO mixing ratios in Beijing are in good agreement with the measurements. Elevated FFCO2 levels are produced by the model in megacities, such as Beijing, Tianjin, Shijiazhuang, and Baoding. The model result shows that FFCO2 mixing ratios are significantly correlated with observed total CO2, CO, and PM2.5 concentrations in Beijing. Sensitivity experiments show that Beijing FFCO2 is mainly from industry and residential emissions (35% for each), followed by power plant (21%) and transportation (9%) emissions in January 2014. Spatially, the largest contributor for Beijing FFCO2 is the local source, and regional transport also plays an important role in winter. The impact of regional transport is associated with wind direction, in which south/east (north/west) wind tends to accumulate (dilute) Beijing FFCO2. In addition, the roles of regional transport during haze and clean episodes are significantly distinct in winter, and more contribution is found in haze episodes.
Propagation of toxic substances in the urban atmosphere: A complex network perspective Atmos. Environ. (IF 3.708) Pub Date : 2018-11-02 Sofia Fellini, Pietro Salizzoni, Lionel Soulhac, Luca Ridolfi
Impact of bay breeze and thunderstorm circulations on surface ozone at a site along the Chesapeake Bay 2011–2016 Atmos. Environ. (IF 3.708) Pub Date : 2018-11-02 Gina M. Mazzuca, Kenneth E. Pickering, David A. New, Joel Dreessen, Russell R. Dickerson
Coastal regions are frequently subject to higher concentrations of ozone (O3) than areas farther inland due to thermally-direct recirculation (e.g., sea/bay breezes) of pollutants during summer months. Along with high O3 concentrations on polluted days, a bay breeze (in this case, the Chesapeake Bay breeze) causes low-level convergence over the land, which can lead to deep convection even on days without any large-scale convective forcing, altering both the local flow pattern and the concentrations and distributions of pollutants. Presented here is a bay breeze and thunderstorm climatology for Edgewood, MD, a coastal site along the Chesapeake Bay, from June, July, and August 2011–2016 between 11 and 19 EST (UTC-5). Using meteorological data from the Maryland Department of the Environment (MDE), bay breezes are identified by an automated detection algorithm, the Bay-breeze Identification Algorithm (BIA), customized for the complex coastline of river inlets within the Chesapeake Bay area. Additionally, thunderstorm vs. non-thunderstorm days are analyzed using gridded Earth Networks lightning data (ENTLN) within an influential radius of the site. The effects of bay breezes and deep convection on local O3 is quantified. The highest daily conditional mean O3 for all years was observed on bay breeze days, and the lowest on days with thunderstorms only (no bay breeze). Additionally, 39% of O3 exceedance days within the analysis time period were also bay breeze days. However, as ozone precursor emissions have fallen, the relationship between bay breezes and high O3 has diminished. While days with thunderstorms only (no bay breeze) were associated with the lowest daily mean O3, there were O3 events on some thunderstorm days, especially if there was also a bay breeze. Twenty-four percent of the total ozone exceedance days had a thunderstorm, demonstrating that thunderstorm days should not be assumed to be clean days, as boundary-layer venting and downdraft mixing depends on the thunderstorm duration and type (e.g., non-frontal/pop-up convection allowed slightly higher O3 concentrations than did frontal convection). These results illustrate the significant role that localized meteorological events that are difficult to predict play in modulating air pollution where many of the world's cities lie – near bodies of water.
Exploring the temporal trends and seasonal behaviour of tropospheric trace gases over Pakistan by exploiting satellite observations Atmos. Environ. (IF 3.708) Pub Date : 2018-11-02 Naila Zeb, Muhammad Fahim Khokhar, Andrea Pozzer, Saud Ahmed Khan
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- Acc. Chem. Res.
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- New J. Chem.
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- npj 2D Mater. Appl.
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- npj Flex. Electron.
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- PLOS ONE
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- Polym. Degrad. Stabil.
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- Polym. Rev.
- Powder Technol.
- Proc. Combust. Inst.
- Prog. Cryst. Growth Ch. Mater.
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- Prog. Photovoltaics
- Prog. Polym. Sci.
- Prog. Solid State Chem.