Air quality affects both ecosystems and human health. To assess the effects of air pollution, spatially explicit information of pollutants is needed. Atmospheric chemistry transport models are the best option to estimate concentrations and deposition of pollutants from local to regional scales. However, concentration and deposition maps derived from available regional and global models are typically given at spatial resolutions of 10–50 km and do not contain information at sufficiently high spatial resolution (i.e. ≤ 5 km × 5 km) to identify risks and to develop solutions to protect ecosystems and human health. Here we provide deposition and concentrations of nitrogen (N) and sulfur (S) at a 5 km × 5 km resolution for the western Iberian Peninsula. The new maps are a major improvement over existing information due to the higher spatial resolution. Comparisons with measurements indicate that all maps for N compounds are fit for purpose. Nitrogen deposition in W Iberia ranged from 3 to 38.6 kg N·ha−1·year−1, averaging ∼8.2 kg N·ha−1·year−1 with a higher contribution from reduced N forms (62%). Deposition of oxidized forms mainly prevailed in urban and industrial areas and in coastal locations. The contribution of wet deposition was slightly higher (55%) than dry deposition and more important in the North, following the pattern of precipitation. Dry deposition is higher closer to emission sources. Due to their high spatial resolution, these maps can be used for policy development to support ecosystem protection, through the identification of areas at greater risk due to high N deposition. National policy efforts to reduce N pollution must, foremost, target ammonia (NH3) emissions in rural areas and oxidized nitrogen (NOx) emissions in urban and industrialized areas.

This study investigated particulate and gaseous emission factors (EFs) from an ocean-going cargo vessel operating under different real-world conditions. EFs were determined for criteria gaseous (including NO, NO2, CO, CO2, SO2) and particulate pollutants (including PM2.5 and PM2.5 components, such as organic carbon, elemental carbon, BC, water-soluble inorganic ions and metal elements). The results showed that the gaseous emissions were dominated by CO2 and NO, the EFs of which were ranging from 489 g/kWh to 1040 g/kWh, and 11.2 g/kWh to 29.1 g/kWh, respectively. And the EFs of PM2.5 were ranging from 0.13 g/kWh to 1.12 g/kWh. Vanadium, silicon, calcium and nickel were the main contributors to the presence of inorganic metal elements. Marine diesel oil (MDO) and heavy fuel oil (HFO) were used in the cargo vessels sailing along the coastline and in the ocean, respectively. When using MDO instead of HFO, the SO2, NOX and PM2.5 emissions were reduced by 5%, 90% and 60%, respectively. There seemed no obvious effect of the fuel type on the CO2 emission. Besides, the CO2 and SO2 emissions of HFO were linearly correlated with PM2.5. Moreover, the energy efficiency management system (EEMS) was used to estimate the relationship between emissions and engine working conditions. Effective thermal efficiency (ηet) was calculated based on combustion status. CO and BC decreased with increasing ηet for both HFO and MDO, while NO increased with increasing ηet. These results could provide important data support for the use of certification values for emissions inventories.

Volatile organic compounds (VOCs) of motor vehicles contribute greatly to ground-level ozone formation, especially in the megacity regions. While the variations of tailpipe VOC emissions along with the vehicle technologies and road conditions are rarely investigated systematically. Thus, on-road tailpipe VOC emissions from in-use vehicles, including light-duty gasoline vehicles (LDGV), light-duty diesel trucks (LDDT), heavy-duty diesel truck (HDDT) and liquefied petroleum gas-electric hybrid bus (LPGB), were sampled with a combined portable emission measurement system (PEMS). A total of 102 individual VOC species were quantified by a gas chromatography mass spectrometry detector (GC-MSD), and the maximum incremental reactivity (MIR) scale was used to calculate the ozone formation potentials (OFPs). Results showed that aromatics and alkanes were the major VOC groups regardless of the vehicle type, accounting for 68.1–98.0%. For the LDGV, i-pentane, acetone, and propane were the top three VOC species. Naphthalene, dodecane and n-undecane were main VOC constituents in the diesel exhaust. Acetone was the most abundant VOC species for the LPGB, followed by i-pentane, i-butane and n-butane. Road conditions had a significant impact on the VOC emission factors. Specifically, emission factors on urban roads were 3.3–7.0 times those on the highway. The OFPs were 70.7, 128.1, 2189.4 and 124.7 mg O3/km for the LDGV, LDDT, HDDT and LPGB, respectively; aromatics were the main contributors, occupying 49.6–93.4% of the total OFPs. Results indicated that emission factors and dominant species of VOCs were strongly affected by vehicle technologies and road conditions, but aromatics were the major group for both VOC composition and OFPs.

Black carbon (BC) is a major component in atmospheric particulate matter (PM), which causes adverse health impacts and contributes significantly to climate change. Without widespread and accurate BC measurements, it remains difficult to track incomplete combustion sources and reduce BC emissions. Currently commercial BC sensors remain too costly to be deployed widely. In this work, a fast, cost-effective, and easily accessible method based on a smartphone camera was used to quantify color information of PM collected on filters to estimate BC and elemental carbon (EC) loadings. A robust RGB (red, green, blue)-based linear interaction model was built and validated using 1,878 PM samples collected in three different regions with collocated BC and EC measurements. After applying image correction methods, this model shows a good predictability with an R-squared (R2) of 0.904 with state-of-the-art BC measurement techniques, and a coefficient of variation of the root mean square error (CV(RMSE)) of 25.3% despite the complex sources and different reference measurement techniques. This work validates the viabilities of using smartphones to quantify BC or EC loading on PM filters with a unified model and track incomplete combustion sources.

This study investigates the impact of Arctic Oscillation (AO) abnormalities on the haze days in China for 57 winters from 1961 to 2017. The results reveal that that AO abnormalities mainly affected meteorological conditions and haze pollution in northern and central China, while their impact on the southeast coastal and Guangdong-Guangxi regions is not significant. During years with an abnormally high AO index (AOI) in winter, the number of haze days increased in northern and central China, especially in the Shanxi–Shandong–Hebei–Beijing–Tianjin and Hubei–Hunan–Henan–Jiangxi regions, while the number of haze days decreased during years of abnormally low AOI. When in the years of abnormally high AOI, the weakening of the East Asian trough caused the decrease of the meridional circulation and the increase of zonal winds compared with normal years. Furthermore, the weakening of the Siberian high pressure and the enhancement of the westerly circulation affected several meteorological factors, including the boundary layer height, surface temperature, wind speeds, and precipitations. These changes effectively inhibited the development of low-level vertical motion and the vertical diffusion of pollutants in the air, leading to the accumulation of haze pollution. The situation was the opposite for low AOI years, but the impact on the meteorological conditions was relatively weak compared to that during high AOI years. The impacts of the regional characteristics of AO abnormalities on the haze days are also investigated in this study.

Background Short-term exposure to ambient air pollution (AAP) has been widely linked to asthma morbidity such as outpatient and emergency visits and hospitalization. Up to date, however, the acute effects of AAP exposure on asthma mortality remained largely unknown possibly due to the rare occurrence of asthma deaths. Objectives This study aimed to investigate whether the death risks from asthma are triggered by short-term AAP exposures in a Chinese urban population who suffered poor air quality. Methods 1385 asthma death cases were identified from the total 61.3 thousand death records in two urban districts in Wuhan, central China, 2003–2013. We performed a time-stratified case-crossover design and conditional logistic regression models were applied to assess short-term associations of air pollutants (particulate matter with aerodynamic diameter ≤10 μm [PM10], sulfur dioxide [SO2], and nitrogen dioxide [NO2]) along different exposure days with asthma mortality. Results A total of 1385 case days and 4668 control days were investigated during the study period. Daily mean concentrations of PM10, SO2, and NO2 were 116.6 μg/m3, 53.4 μg/m3, and 60.7 μg/m3, respectively. A 10 μg/m3 rise in exposure to SO2 and NO2 at 2 days prior to death (lag 2 days), was associated with increased asthma death risks of 2.9% (odds ratio [OR] = 1.029, 95% confidence interval [CI]: 1.006, 1.053) and 4.3% (OR = 1.043, 95% CI: 1.012, 1.076), respectively. No evident PM10-asthma associations were identified in all subpopulations except for those aged 85 + years (OR = 1.022, 95% CI: 1.001 to 1.044). In our stratified analyses, significant effects of SO2 and NO2 were only observed in female, the older elderly, 7+ years-educated and unmarried persons, as well as those died outside the hospital and in cold season. We observed some evidence for effect modification by age, with p-values of 0.032 for PM10 and 0.051 for SO2, suggesting higher vulnerability to air pollution among the older asthma cases. Conclusions This study provided suggestive evidence for the short-term association between air pollution exposure and asthma death in highly polluted urban areas. Several days’ high-level exposures to air pollutants, particularly SO2 and NO2, may elevate risks of asthma death. Our findings highlighted the potential health benefits from intervention and preventive actions targeted to reducing AAP exposure among asthma patients.

Prescribed burning is a prominent source of PM2.5 in the southeastern U.S. An air quality forecasting system called HiRes2 currently serves most areas in the southeastern U.S. to forecast PM2.5 concentrations one day in advance, including the impact of forecast prescribed burning activity. The output prescribed fire impact from the HiRes2 forecasting system is the combined impact of all the fires in the domain. When there are many fires close to each other, it is difficult to distinguish the ones that are more likely to lead to air quality issues. A novel source apportionment method, Dispersive Apportionment of Source Impacts (DASI), has been developed and applied to split the combined prescribed fire impact obtained from a chemical transport model (CTM) by using simulated fields from a dispersion model. Comparisons of apportioned fire impacts with single burn impacts simulated directly by the CTM show that DASI works well with large and small fires that do not have too much interaction with other fires. Individual fire impacts obtained by splitting the combined fire impacts from CTMs could help local land and air quality managers to evaluate which burns should be allowed or restricted based on their individual impacts on air quality and public health in areas of concern.

Background Ambient air pollution and cigarette smoking are two significant risk factors for mortality; however, less is known about their interaction. Objectives We aimed to assess effect modification of cigarette smoking on the association between short-term exposure to air pollution and mortality in the Chinese Elderly Health Service Cohort in Hong Kong. Methods We included 16,290 Chinese elders aged 65 years or older who died between 1 July 1998 and 31 December 2011. Smoking history was collected through face-to-face interviews by registered nurses or doctors using a standardized structured questionnaire when they were recruited into the cohort. We used a time-stratified case-crossover approach to estimate the percent excess risk (ER%) of all-natural mortality per 10 μg/m3 increase in fine particulate matter (PM2.5), respirable particulate matter (PM10), and nitrogen dioxide (NO2) among current-, ex-, and never-smokers, and to estimate the additional percent excess risk (ΔER%) for current- and ex-smokers relative to never-smokers. We performed secondary analysis to assess whether the estimated additional risks varied by personal characteristics. Results There were a greater ER % associated with air pollutants among current- and ex-smokers relative to never-smokers. We found ΔER% per 10 μg/m3 increase in air pollutants was statistically significant for PM2.5 among ex-smokers [2.63% (95% CI: 0.39%, 4.88%) at 1 day prior to death (lag1)], and PM10 among current-smokers [2.21% (95% CI: 0.08%, 4.33%) at lag1] and ex-smokers [1.96% (95% CI: 0.26%, 3.65%) at lag1]. The increased risks associated with cigarette smoking were more pronounced among males, overweight or obese elders, elders with three or more comorbidities, or elders received primary or lower education. Conclusion Ever-smokers were more susceptible to excess mortality risk associated with daily air pollution, especially for males, overweight or obese elders, and those with poor health conditions or received lower educational attainment. Tobacco control can reduce the health burdens attributable to air pollution.

Modern dust plays essential roles in marine and climate processes, which bring continental material to the ocean and sensitivity in marine ecosystems. However, the atmospheric dust deposition process has rarely been studied in the South China Sea (SCS). Here, we present 51 atmospheric dust samples, collected along the SCS, to investigate the grain size distribution, depositional flux, and features revealed by scanning electron microscopy, combined with 5-day back trajectories to indicate the present-day dust deposition process for the first time. The grain size distribution and depositional flux of aerosol samples illustrate the seasonal trend, coarser particle and higher flux mass in winter than summer, reflected in average grain size (5.75 μm during winter and 3.62 μm from summer) and 1.4 times depositional flux in former than that in summer, both are related to the transport pathway and power of the East Asian monsoon. Modeled 5-day back trajectories of dust samples suggest a southwesterly transport pathway in summer and the Southeast Asian monsoon as a possible source of the dust loading, while the northeast winds drove the aeolian dust transport during the winter monsoon from the Asian continent. Meanwhile, westerly circulation conveys the fine particles (∼0.63 μm) as the stable terrigenous component into the SCS, deposited through the entire dust deposition process from the atmosphere and water to the surface sediment. Furthermore, the surface of quartz particles from atmospheric dust shows the unique structure in the aeolian environment as a reference to distinguish the different continental components in the sediments. This study provides new insights into the present-day dust deposition process in the SCS, significantly extending the current understanding of the relationship between atmospheric dust and the marginal sea.

Serious haze pollution (e.g., PM2.5, particulate matter with aerodynamic diameters less than 2.5 μm) and increased ground-level ozone are severe air quality issues in China. In Beijing-Tianjin-Hebei and the surrounding areas (denoted as BTH&SA), although recently the particulate matter pollution appeared to be under control due to stringent pollution mitigation measures, ozone pollution rebounded rapidly, especially during summers. Thus, the exploration of strategies for efficiently lowering both ground-level ozone and PM2.5 concentrations is urgently needed. In this study, we target on the precursors contributing to both ozone and PM2.5 formation (i.e., NOx and volatile organic compounds (VOCs)) and adopt a Combined Empirical Kinetics Modeling Approach (CEKMA) to synthetically evaluate the cost-effective mitigation strategies for air quality control. We find that over the BTH&SA region, the choice of mitigation strategy in the initial stage (e.g., within 20% reductions on NOx or VOCs emissions) is critical because NOx-focused strategies may exacerbate O3 pollution. In addition, equally reducing NOx and VOCs emissions may have the least benefit for air pollution improvement. From a long-term perspective, we suggest reducing VOCs emissions by ∼60% and NOx emissions by ∼20% in the first stage, thereby avoiding the potential increase in ambient O3. Then in the second stage, the remaining VOCs and NOx emissions should be phased out to reach a deep mitigation of PM2.5 and O3. With those steps, both PM2.5 and ozone can be mitigated efficiently over the BTH&SA region.

Interactions between the spatiotemporal distribution of pollutants and the structure of the atmospheric boundary layer were studied using data obtained by GPS (Global Positioning System) sounding balloons in an intensive observation period from December 2018 to January 2019 at the Dezhou experimental station in the North China Plain. Under haze weather conditions, negligible variation or a slight increase in temperature, higher relative humidity (RH) and lower wind speed with uncertain wind direction are common characteristics. The concentration distribution of particulate matter ≤2.5 μm (PM2.5) has a close relationship with the inversion layer, which contributes to the accumulation of PM2.5 in the lower atmosphere. The reduction of pollutants suspended in the upper layer during haze periods is closely related to low-level jets and intermittent turbulence. Higher RH values are also favourable for the formation of heavy haze, and the value of PM2.5 increases with an increase in humidity. During hazy days, the heat fluxes and turbulent kinetic energy (TKE) are much smaller than those during clear days. The values of the average maxima of net radiation, sensible heat flux, and latent heat flux are 154, 76, and 15 W/m2, respectively, and the value of TKE is approximately 0.67 m2/s2. The decrease in atmospheric boundary layer height (ABLH) is caused by weaker turbulent transfer during haze episodes. The ABLH is approximately 400 m during the daytime and 240 m at night. The power function relationship is shown by a negative correlation between the ABLH and surface PM2.5 concentration in the convective boundary layer.

With Tibetan Plateau higher than 4 km to the west, the location of Sichuan Basin is unique all around the world and provides a good platform to study air pollution in the urban agglomerations over the complex terrain. To fill in the blanks on vertical distributions of PM1 (the particles smaller than 1 μm) and carbonaceous aerosols within the basin, by means of high topographic relief, PM1 were off-line sampled during 20 January to 2 February 2018 at eight sites with increasing altitudes from the basin to southeastern margins of the Tibetan Plateau. The regional potential sources for each site were revealed by HYbrid-Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model and concentration-weighted trajectory (CWT) method. The lowest carbonaceous aerosol levels occurred at Lixian, while the highest OC (organic carbon) (EC, elemental carbon) was at Hongyuan (the altitude of 3500 m) (Ande, a rural site) due to more primary emissions. The pollutants inside the basin can be transported the altitudes from 2 km to 3 km by vertical dispersion, but they cannot be dispersed to higher altitudes. The vertical stratification of the pollutants was obvious and easily formed “high-low-high” pattern from Sichuan Basin to southeastern Tibetan Plateau, especially during highly polluted episodes. The regional potential sources significantly varied as the increased altitudes. Regional pollution was significant inside the basin. The sources at the altitudes from 2 km to 3 km originated from southeastern margins of the Plateau and surrounding cities, while those at higher altitudes were transported from southeastern margins of the Plateau. The impact of basic meteorological variables (temperature, wind speed and vapor pressure) on carbonaceous aerosols was opposite between the basin and Plateau sites. This study was essential to understanding formation mechanisms of severe pollution episodes and thus to making control measures for the urban agglomerations inside the mountainous terrain.

A record-breaking episode of highly concentrated particulate matter (PM) with diameters ≤ 2.5 μm (PM2.5) and ≤10 μm (PM10) occurred in South Korea during the period January 11–15, 2019: the hourly PM2.5 (PM10) in Seoul was 188 μg m−3 (262 μg m−3) on January 14. At the Baengnyeong and Socheongcho stations, located in the Yellow Sea between China and Korea, the hourly PM2.5 concentration reached up to 155 μg m−3 and 119.8 μg m−3, respectively, 16−19-h prior to this episode. This and the fact that the maximum PM10 concentration at Baengnyeong was 199 μg m−3 indicated a westerly transport of air pollutants. Satellite observations and 72-h back trajectory analysis clearly indicate that air pollutants from China flowed into Korea via the westerlies. According to contribution analysis using particulate matter source apportionment technology in the Comprehensive Air-quality Model with extension, air pollutants originating from northeastern China including Hebei and Shandong provinces were largely linked to the present record-breaking high concentration event in Seoul. This study will elucidate the mechanism of transboundary transport of air pollutants and help East Asian countries cooperate on air quality management.

The aerosol change over the Tibetan Plateau (TP) is poorly understood due to the scarcity of aerosol measurements over the TP. The aerosol optical properties were measured with a CE-318 sun photometer from January to December in 2017 at the Litang station (30.00°N, 100.16°E, 3950.5 m a.s.l.) over the eastern edge of the TP to characterize the variations in the aerosol optical properties and assess the applicability of MODIS AOD products at the eastern edge of TP. The analyses show that the annual mean aerosol optical depth at 440 nm (AOD440nm) is 0.08 ± 0.03. The mean annual Angström exponent between 440 and 870 nm (AE440–870nm) is 0.72 ± 0.23. The monthly-averaged AOD440nm exhibits a maximum (0.11 ± 0.04) in July and minimum (0.05 ± 0.02) in January, while the monthly mean AE440–870nm shows a maximum (1.08 ± 0.19) in July and minimum (0.48 ± 0.32) in February. The findings based on measured AOD440nm and AE440–870nm indicate low AOD, dominated by coarse particles in winter and fine particles in summer over the eastern TP edge. Three datasets of MODIS AOD products with 3 km spatial resolution as well as with 10 km spatial resolution based on Dark Target (DT) and Deep Blue (DB) algorithms are validated using the ground-based measurements over the eastern edge of the TP. Although the validations show a low accuracy of MODIS AOD products of the three datasets over this TP region, the MODIS AOD products based on the DB algorithm with 10 km resolution could be used in the atmospheric environment over the eastern edge of the TP based on the best match between AOD data and ground-based measurements, the lowest retrieval error, and the largest percentage falling within the expected error envelope.

Pollution weather may cause serious damages to human life and property. Meteorological conditions like large-scale circulation can affect the formation and dissipation of pollution weather. We apply the hierarchical clustering method to classify circulation patterns based on the National Centers for Environmental Prediction (NCEP) Final Operational Global Analysis (FNL) sea level pressure (SLP) daily data and investigate their features during the formation and dissipation process of the defined 31 continuous pollution weather (CPW) cases in the Sichuan Basin using the meteorological data from 104 surface observation stations during 2007–2017. We find that the Sichuan Basin during the formation process is controlled by the large scale high-pressure circulation at sea level, and the SLP can be divided into high-pressure front type FC1 (32%) with the high pressure located in the west of the Basin, weak high-pressure type FC2 (35%) with the weak high pressure located in the Basin, and uniform pressure field type FC3 (33%) with the near homogeneous pressure distributed in the Basin. The Sichuan Basin during the dissipation process is dominated by the low-pressure circulation at sea level, and the SLP can be classified as low-pressure type DC1 (35%) with the low pressure centralize in the Basin, low-pressure front type DC2 (38%) with the low pressure center in the west of the Basin, and low-pressure bottom type DC3 (27%) with the low pressure in the north of the Basin. Besides, the wind, relative humidity, geopotential height and temperature data are used to explore the formation and dissipation mechanisms of the CPW. The wind speed and temperature are lower during the formation phase of the CPW compared to those from the dissipation phase. Furthermore, we estimate the effects of the CPW on pollutants based on the air quality index and Particulate Matter (PM10 and PM2.5) concentration from environmental protection monitoring data during 2013–2017. The FC2 type shows the strongest enhancement of pollutants (36%), and the DC3 circumstance generates the most efficient scavenging mechanism to dispel pollutants (−57%).

Ozone is one of remaining air quality issues in Japan. Effective strategies are required to reduce ozone at the ground level. Regional chemical transport models are useful in investigating relationships between precursor emissions and ambient concentrations of secondary pollutants including ozone. Model performance on ozone concentrations over urban areas in Japan were thoroughly evaluated in model inter-comparisons conducted in Japan's study for reference air quality modeling (J-STREAM). Specifically, 33 models with different configurations including the Community Multiscale Air Quality Modeling System (CMAQ), the Comprehensive Air Quality Model with Extensions (CAMx), and the Weather Research and Forecasting (WRF) model coupled with Chemistry (WRF-Chem) participated. They realized inter-comparisons with an unprecedented number of different model configurations. All the participating models overestimated ozone concentrations by 22 ± 4.6 ppb over urban areas in Japan during the summer. Spatial and temporal variations in model performance suggest the influence of background ozone concentrations. Based on differences in the participating model configurations, halogen chemistry and deposition, dry deposition velocity, precursor emissions in other countries, and vertical transport were identified as the key factors influencing simulated background ozone concentrations. Specific sensitivity analyses were conducted to evaluate the effects of the key influencing factors. Halogen chemistry and deposition implemented in recent versions of CMAQ caused more than 10 ppb reduction of simulated ozone over the ocean surrounding Japan, while the original dry deposition schemes used in CAMx and WRF-Chem, without any effect of halogen, can also cause larger dry deposition. Horizontal and downward transport of ozone kept in a residual layer over the continent can spread the effect of precursor emissions in other countries to downwind regions, including Japan. Differences in vertical transport can alter the spatial extent of their effects. It is essential to improve the influence of the aforementioned key factors to realize better model performance on ozone concentrations over urban areas, not only in Japan, but all over the world.

Open biomass burning is one of the largest sources of aerosols and reactive trace gases into the atmosphere, having a significant effect on earth's radiative budget and air quality. Biomass burning degrades air quality by increasing both particulate matter and ozone levels. Unlike aerosols, ozone is not directly emitted in fires but it is frequently formed in ageing plumes. This is not surprising, as many of the reactive trace gases emitted in biomass burning including nitrogen oxides, carbon monoxide and volatile organic compounds, act as precursors for ozone formation. Geographically, Africa is the most significant source region of biomass burning emissions. Here, we report rapid ozone formation in daytime savanna and grassland fire plumes observed in South Africa. We observed higher ozone production in more flaming cases for plumes fresher than 1.5h. However, in plumes aged >1.5h combustion characteristics have no effect, but ozone production is positively correlated with nitrogen oxides. Furthermore, the plumes with highest ozone production also had the strongest secondary aerosol formation during plume ageing. Additionally, we report emission factors of nitric oxide and sulphur dioxide for southern African savanna and grassland fires. SO2 emission factor was on average 1.1 g kg−1, which is two to three times higher than previous observations for savanna and grassland. On the other hand, the average NO emission factor (2.6 g kg−1) agrees well with previous observations.

Fine particulate matter (PM2.5) concentration that exceeds standards is causing poor air quality in most Chinese cities. Meteorological conditions are an important factor affecting PM2.5 concentration, but few quantitative studies have been conducted on the effects of long-term and large-scale changes in meteorological factors on PM2.5 pollution. In this study, a Weather Research and Forecasting/Community Multiscale Air Quality (WRF/CMAQ) modeling system was applied to study the spatial and temporal distributions of the impact of meteorological conditions on PM2.5 pollution in China from 2000 to 2017. During the study period, Me-PM2.5 decreased in general (P = 0.0018) in nationwide, and showed significant spatiotemporal variations. There was an overall increasing trend for Beijing, Fujian, Shaanxi, Gansu, and Qinghai provinces (P < 0.05) as the meteorological conditions deteriorated, and there was an overall negative trend for nine provinces (P < 0.05) which indicated meteorological conditions were causing a decrease in concentrations. Substantial differences in the impact of meteorological changes on PM2.5 pollution were observed across the provinces, with FMe-PM2.5 (fluctuating range of Me-PM2.5) between 9.3% and 55.1%. In addition, the best, typical, and worst meteorological years were selected based on Me-PM2.5; these should be considered when setting air quality goals and pollution control plans.

This experimental study explored the impacts of some codissolved inorganic ions (in particular, sulfate, nitrate and chloride) on the photo-bleaching kinetics of the aqueous solutions of brown carbon (BrC) extracted from rice-straw smoldering aerosol. All the aqueous BrC solutions showed two distinct phases of decreasing mass absorption coefficient (MAC) with irradiation time, where the first phase (0–1h) was 2.4–5.3 times faster than the second phase (1–3h). Interestingly, the photo-bleaching process was slowed down for both phases when SO42− (0–1h: 0.196±0.02 h−1; 1–3h: 0.045±0.01 h−1), NO3− (0–1h: 0.158±0.004 h−1; 1–3h: 0.066±0.007 h−1) and Cl− (0–1h: 0.169±0.007 h−1; 1–3h: 0.032±0.006 h−1) salt solutions were added separately to the BrC extracts (0–1h: 0.27±0.04 h−1; 1–3h: 0.067±0.01 h−1). Alternatively, the corresponding lifetimes of the light-absorbing organic species were enhanced in the salt-added BrC solutions. In addition, the magnitudes of the fluorescence quantum yields were measured to be of the order of 10−3−10−2, implying that most of the absorbed solar energy would convert into heat rather than fluorescing back into the atmosphere. The findings of this study are suggestive of possible increase in heating of BrC containing atmospheric aqueous bodies like cloud-water, resulting in water evaporation and hence reduced precipitation (semi-direct effect).

A road simulator was used to generate wear particles from the interaction between two tyre brands and a composite pavement. Particle size distributions were monitored using a scanning mobility particle sizer and an aerosol particle sizer. Continuous measurements of particle mass concentrations were also made. Collection of inhalable particles (PM10) was conducted using a high-volume sampler equipped with quartz filters, which were then analysed for organic and elemental carbon, organic constituents and elemental composition. Tyre fragments chopped into tiny chips were also subjected to detailed organic and elemental speciation. The number concentration was dominated by particles <0.5 μm, whereas most of the mass was found in particles >0.5 μm. The emission factor from wear between pavements and tyres was of the order of 2 mg km−1 veh−1. Organic carbon represented about 10% of the PM10 mass, encompassing multiple aliphatic compounds (n-alkanes, alkenes, hopanes, and steranes), PAHs, thiazols, n-alkanols, polyols, some fragrant compounds, sugars, triterpenoids, sterols, phenolic constituents, phthalate plasticisers and several types of acids, among others. The relationship between airborne particulate organic constituents and organic matter in tyre debris is discussed. The detection of compounds that have been extensively used as biomass burning tracers (e.g. retene, dehydroabietic acid and levoglucosan) in both the shredded tiny tyre chips and the wear particles from the interaction between tyres and pavement puts into question their uniqueness as markers of wood combustion. Trace and major elements accounted for about 5% of the mass of the tyre fragments but represented 15–18% of the PM10 from wear, denoting the contribution of mineral elements from the pavement. Sulphur and zinc were abundant constituents in all samples.

Previous research has shown the significant transboundary air pollution (TAP) in China. Despite its adverse environmental and human health impacts, the characteristics and mechanisms of TAP have yet to be fully understood. This study comprehensively analyzed intensive ground and upper levels measurements along with the atmospheric modeling approach to determine the driving meteorological conditions to the formation and evolution of a persistent severe PM2.5 pollution episode in Central-East China (CEC, 112°E −118°E, 30°N −34°N) starting from 18:00 on Dec. 3 to 18:00 on Dec. 5, 2017, which had obvious characteristics of TAP and explosive increases in PM2.5 concentration. We assessed and quantified contributions of local and nonlocal emissions to PM2.5 in the region and different cities during the episode and determined the altitude level at which TAP occurred. Results show that PM2.5 concentration in most cities in CEC region experienced two major increases: the first increase was due to the change in wind direction from south to north, transporting pollutants from north China to CEC; the second increase was driven by several important meteorological factors, including warm/cold advection at different altitudes, large-scale subsidence, and radiative cooling, jointly resulting in a deep (reaching around 800 m) and strong elevated temperature inversion with a significant reduction in mixing layer thickness and thus causing a rapid increase in PM2.5 concentration in CEC region. On average, TAP accounted for 42% of total PM2.5 concentration in the region during the event, in which the TAP impact varied by cities, ranging from ∼26% to ∼70%. Our findings demonstrate the synergetic effect of TAP and large-scale subsidence, providing a critical reference for air pollution forecast and assessment in the eastern China.

Precipitation chemistry and atmospheric nitrogen (N) deposition are of great concern worldwide due to their close relationships with air quality and impacts on ecosystems. However, evaluation of the chemical composition of precipitation and N deposition flux in rural areas of Beijing has received little attention to date. This paper presents the chemical constituents, possible sources and wet deposition fluxes of water-soluble ions (NH4+, NO3−, SO42−, Cl−, Na+, K+, Ca2+, Mg2+) in precipitation samples collected during 2017–2018 at a rural site located at northwest of Beijing city; meanwhile, dry deposition of reactive N species (gaseous ammonia, nitrogen dioxide, nitric acid, and particulate (p) NH4+ and NO3−) were also quantified. During this 2-year period, the volume-weighted mean (VWM) pH of precipitation was 6.73, and all samples had pH values above 6.0. The VWM electric conductivity of precipitation and the mean sum of all measured ions was 43.8 μS cm−1 and 591.9 μeq L−1, respectively, indicating a significant impact of atmospheric pollution. Ca2+ and NH4+ were the dominant neutralizing species for precipitation acidity. Positive matrix factorization analysis further confirmed five sources for water-soluble ions, including sea salt aging, secondary formation, agriculture, crust, and biomass burning. The annual mean wet N deposition was 4.6, 3.4 and 8.0 kg N ha−1 yr−1 for NH4+, NO3− and total inorganic N, respectively. The total dry N deposition was dominated by gaseous ammonia (11.5 kg N ha−1 yr−1). The total N deposition (wet plus dry) was 27.7 kg N ha−1 yr−1, where dry deposition contributed to 75% and wet deposition 25% of the total. The simulations from the GEOS-Chem model indicate that agricultural (fertilizer use and livestock) and nonagricultural sources (industry, power plant, and transportation) are both important contributors to total N deposition. These results could be useful in evaluating/developing emission control policies to protect the eco-environment in Beijing.

In this study, we use the level-1.5 and level-2.0 aerosol optical depth (AOD) from the Aerosol Robotic Network (AERONET) Version 3 dataset at 12 sites in China to evaluate the MODIS Collection 6.1 (C6.1) AOD products retrieved using three distinct algorithms: Dark Target (DT), Deep Blue (DB), and DTB merged from DT and DB from Terra and Aqua. The performance of the three algorithms is evaluated. Based on these evaluations, a simple and efficient AOD retrieval algorithm at a high spatial resolution of 1.0 km for China is proposed. AODs at this spatial resolution over China are then retrieved using the methods of DT and DB, respectively. The evaluation results showed that: (1) there is little difference in the AOD products derived from Terra and Aqua. The differences in the determination coefficient (R2) between the two platforms at most sites are less than 0.05. (2) There are relatively large differences in AODs between the AERONET level-1.5 dataset and MODIS dataset while these differences are mostly filtered out by the quality assurance process of the AERONET level-2.0 dataset. The statistical tests indicate that the MODIS DTB AOD product is generally better than those from the other two algorithms. Using the new algorithm developed in this study, the AODs at a high spatial resolution of 1 km in the whole of China are determined and the results are compared with the MODIS DTB product. The results show that the AODs determined using the new method agree reasonably well with those of the MODIS DTB dataset though the new results have slightly negative biases in the wintertime. However, these negative biases may not be a negative sign due to the fact that the MODIS AODs are subject to a positive bias relative to the AERONET AODs.

BioSampler is now being widely used for bioaerosol sampling. However, the sampling efficiency in wide size range especially for nanoparticles as well as the size-dependent retention efficiency have not been well evaluated until now. Through literature review, theoretic analysis and experiments, this paper reviews the sampling process, collection mechanism and sampling performance of commercial BioSampler including pressure drop as a function of sampling flow rate, the mass loss rate and temperature of the collection fluid as a function of sampling time, the variation of retention efficiency with time, and the sampling efficiency in wide size range from nanometers to microns. The effects of low pressure and high relative humidity on determination of sampling efficiency in literature were carefully analyzed. To compensate the collection fluid loss and extract the insoluble/dissolved sample for further analysis, Continuous-Extraction BioSampler (CEBS) is proposed. The retention efficiency for particles of different sizes as well as the collection efficiency were determined and found to be identical with commercial BioSampler when no steam was introduced into CEBS. Finally, the combination uses of CEBS and Inductively-Coupled-Plasma Mass Spectrometer (ICP-MS) was developed. Exponentially Modified Gaussian (EMG) Model was derived and verified to describe the temporal concentration of the dissolved component originating from individual soluble droplet. Using internal standard calibration method and EMG fitting of signal curve, the target element amount in individual droplet could be determined accurately. For continuously-collected soluble droplet with duration of minutes, the observed signal curve can be described by EMG model and the fitted value of area varies linearly with the sample amount introduced. This paper not only provides comprehensive performance evaluation of commercial BioSampler, but also demonstrates that the proposed CEBS-ICPMS is capable of monitoring environmental coarse aerosol with time resolution of ∼17 min.

The recent AVHRR aerosol products expended from MODIS Deep Blue (DB) algorithm provide an unprecedented long-term data record over land that dates back to 1980s. Unlike previous studies focused on performance of AVHRR retrievals, here we present a critical view into the influence of retrieval frequency on consistency of AVHRR Aerosol Optical Depth (AOD) with other satellite DB products, and application potential in characterizing the dramatic aerosol loading in China. Despite the good consistency of collocated AVHRR, SeaWiFS, and MODIS DB AOD, their different retrieval frequency leads to distinct distribution of annual or seasonal AOD. In particular, the over-strict cloud screening of AVHRR with fewer bands tends to filter out high-AOD and clean bright surface, with the overall AOD frequency only half of MODIS's. Retrieval frequency and selection criterion of AOD quality can determine representativity and consistency of conventional averaged satellite AOD, uncertainties of which should be considered according to specific application purpose. The time series variation of AVHRR AOD shows that early 1990s is a key time point when frequent haze pollution appears and increases in eastern China. By contrast, aerosol loading in 1995–1999 has reached similar level as in 2000s with notable hotspot of high-AOD (∼0.8–0.9) and slight changes. Our results shows that full record of AVHRR aerosol products with corresponding improvement can greatly renew the understanding of aerosols in China.

This work performed a systematic investigation on the aqueous hydroxyl radical (OH) - induced photochemical oxidation of three modestly-soluble precursors from biomass combustion including 4-methylsyringol (DMP), eugenol (Eug), and 2,4,6-trimethylphenol (TRMP) under both simulated sunlight and ultraviolet (UV) light irradiations. An Aerodyne soot particle aerosol mass spectrometer (SP-AMS) was used to monitor the bulk chemical and elemental compositions of aqueous secondary organic aerosol (aqSOA) formed. AqSOA mass yields varied in ranges of 80–190% and 0–200% under sunlight and UV light conditions, respectively. AqSOA oxygen-to-carbon (O/C) ratio and carbon oxidation state increased steadily under sunlight + OH condition, but increased then decreased under UV + OH condition. Organic acids including malic acid, glycolic acid, formic acid and oxalic acid were formed, and their total accounted for ∼12% of SOA mass. The UV–vis spectral change suggested formation of light-absorbing organics. Reaction pathways were proposed by combining gas chromatography-mass spectrometry (GC-MS) and SP-AMS results. Under sunlight + OH condition, oligomerization, functionalization, and fragmentation processes all involved in aqSOA evolution, with more contribution from functionalization via hydroxylation and oxygenation reactions. Reaction mechanism of UV + OH oxidation was initially dominated by functionalization then by fragmentation, indicating by the decrease of total organic carbon (TOC) contents, formation of small organic acids and low-molecular-weight products. Our work highlight that combination of SP-AMS with GC-MS is a powerful method for laboratory investigation of aqueous-phase reactions.

Increasing trends in summer-time temperature maxima (Tmax) over India, show consequent increases in the intensity and frequency of heatwave events in recent years. Heat waves have been largely attributed to large-scale meteorological blocking, characterized by subsidence, clear skies and low soil moisture, in observational studies, or greenhouse gas enhancements in model studies. While radiative effects of absorbing aerosols are acknowledged, the association of absorbing aerosols with temperature maxima has not been investigated comprehensively. In the current study, statistical tools (such as correlation and Granger causality) were applied to long term (1979–2013) satellite and ground based observations to evaluate influence of absorbing aerosols on Tmax in north-west India (Tmax-NW). Regional absorbing aerosol index (AAI) in the north-west (AAI-NW) and central-India (AAI-CI) showed co-variability with Tmax-NW, implying connections to both local and non-local absorbing aerosols. The effects persisted on seasonal and heatwave event scales, becoming stronger on heatwave days with presence of enhanced AAI loadings. Causal effects of AAI-NW and AAI-CI were identified on Tmax-NW with a lag of 1–11 days, across multiple years, thereby establishing the influence of absorbing aerosols on heatwave events. The absence of confounding effects of surface pressure on these links suggests that, even during heat wave events linked to atmospheric blocking, absorbing aerosols can further enhance temperature maxima and related heat-wave intensity.

Observations from the Ozone Monitoring Instrument (OMI), onboard the NASA's Earth Observing System (EOS) Aura satellite, reveal a large SO2 “hotspot” over Morbi, Gujarat, India, while the available emissions inventories do not report any major sources in this region. There are no industries that are typically associated with the elevated SO2 such as large power plants, smelters, or oil refineries in the Morbi region. Our analysis shows that the elevated SO2 source is attributed to the ceramic industries in an area of ∼7 × 7 km2 near the city. OMI-estimated SO2 emissions from the Morbi ceramic industries have been near or above 100 kt y−1 since 2009, which are similar to emission levels from larger Indian oil refineries (such as Essar and Jamnagar) and power stations (such as Mundra Thermal Power Station and Ultra Mega Power Plant) located in Gujarat, India. According to OMI measurements, the SO2 emissions from the Morbi ceramic industries are presently five times higher than they were in 2005. This study demonstrates that in the absence of any other information about SO2 emissions from the ceramic industry, these satellite-based estimates can fill the gap in emission inventories in a timely fashion.

Land use regression (LUR) modeling has been applied to study the spatiotemporal patterns of air pollution, which when combined with human space-time activity, is important in understanding the health effects of air pollution. However, most of these studies focus either on the temporal or the spatial domain and do not consider the variability in both space and time. A temporally aggregated model does not reflect the temporal variability caused by traffic and atmospheric conditions and leads to inaccurate estimation of personal exposure. Besides, most studies focus on a single air pollutant (e.g., O3, NO2, or NO). These pollutants have a strong interaction due to photochemical processes. For studying relations between spatial and temporal patterns in these pollutants it is preferable to use a uniform data source and modelling approach which makes comparison of pollution surfaces between pollutants more reliable as they are produced with the same methodology. We developed temporal land use regression models of O3, NO2 and NO to study the co-variability of these pollutants and the relations with typical weather conditions over the year. We use hourly concentrations from the measurement network of the Dutch National Institute for Public Health and the Environment and aggregate them by hour, for weekday/weekend and month, and fit a regression model for each hour of the day. 70 candidate predictors that are known to have a strong relationship with combustion-related emissions are evaluated in the LUR modelling process. For all pollutants, the optimal LUR was identified with 4 predictors and the temporal variability was determined by the explained variance of each temporal model. Our temporal models for O3, NO2, and NO strongly reflect the photochemical processes in space and time. O3 shows a high background value throughout the day and only dips in the (close) vicinity of roads. The diminishing rate is affected by traffic intensity. The NO2 LUR is validated against NO2 measurements from the Traffic-Related Air pollution and Children's respiratory HEalth and Allergies (TRACHEA) study, resulting in an R2 of 0.61.

Inhalable particulate matter (size <2.5 μm: PM2.5) inside commuting and tourist buses moving through the city of Barcelona, Spain, was chemically analysed. The analyses show PM dominated by organic carbon (mostly 10–20 μg/m3) and elemental carbon (mostly 3–6 μg/m3; OC/EC = 3.4), followed by SO42, Fe, Ca, K, Al2O3, Mg, and Na, with calculated mineral content being around one third that of total carbon. Elemental carbon levels are higher inside diesel buses than those powered by natural gas or electricity, and higher in the upper floor of open-top double decker tourist buses than in the lower floor. Overall, major element concentrations inside the buses are typically 2–8 times higher than 24 h-averaged urban background levels, although some metallic trace elements, notably Cu and Sb, are exceptionally enriched due to the presence of brake particles, especially on routes involving higher gradients and therefore more brake use. In contrast, Cu and Sb concentrations in electric buses are unexceptional, presumably because these buses rely more on regenerative braking and are hermetically sealed when moving. Seasonal differences reveal PM to be more mineral in winter (Al2O3 1.3 μg/m3 vs. summer average of 0.3 μg/m3), with summer enrichment in Na, Mg, P, V, Ni and SO42− being attributed to marine aerosols contaminated by port emissions. Source apportionment calculations identify 6 main factors: road dust resuspension, metalliferous (brake wear and metallurgy), local urban dust, secondary sulphate and shipping (6%), vehicle exhaust (19%), and an indoor source (46%) interpreted as likely related to the textile fibres and skin flakes of bus occupants. Volatile Organic Compounds measured inside all buses except one were dominated by 2-Methylpentane (14–36 μg/m3), Toluene (10–30 μg/m3), Xylene isomers (10–28 μg/m3, with m- » o- > p-Xylene) and n-Pentane (5–15 μg/m3). ƩBTEX concentrations were <70 μg/m3, with Toluene being commonest, followed by m-Xylene, with p-Xylene, o-Xylene and Ethylbenzene each below 7 μg/m3 and Benzene concentrations always less than the EU limit value of 5 μg/m3. The VOCs mixture is similar to that recently reported from inside Barcelona taxis (although inside the larger volume bus VOC concentrations are lower than in the taxis) and is interpreted as providing a chemical fingerprint characterising traffic-contaminated ambient air in the city road environment. The notable exception to the VOC content was a brand new hybrid diesel bus still offgassing volatiles to such an extent that Ʃ(alkane + alkene + aromatic) indoor concentrations exceeded 800 μg/m3, with ƩBTEX ten times higher than normal.

Simultaneous field measurements of ozone (O3) and its precursors were conducted at an urban site (Zi Yang, ZY) and a suburban site (Huang Pi, HP) in August 2018 in Wuhan, China. The observation results revealed that the mean levels of nitric oxide (NO), nitrogen dioxide (NO2), carbon monoxide (CO) and non-methane hydrocarbons (NMHCs) were higher at ZY than those detected at HP, while the opposite trend was observed for O3 levels. Compared to non-O3 episode days, higher levels of O3 and its precursors (i.e. NMHCs, NO and CO) were observed on O3 episode days at both ZY and HP. A chemical box model was used to investigate the O3 photochemistry on O3 episode days and non-O3 episode days at ZY and HP, and the O3 production was found to be dominated by the reaction of HO2 + NO at the two sites. In terms of O3 destruction, OH + NO2 was the major contributor at ZY, while the highest contribution at HP was from the reaction of O(1D) + H2O. The net O3 production rates increased significantly from non-O3 episode days to O3 episode days at both ZY and HP, indicating increased O3 accumulation on O3 episode days. In addition, the model simulation indicated that O3 formation was controlled by volatile organic compounds (VOCs) at ZY, whereas O3 formation was cooperative controlled by VOCs and NO at HP. Overall, these findings can provide valuable information on formulating and implementing O3 control strategies in urban and suburban areas in China.

Recently, NASA's Multiangle Imaging SpectroRadiometer (MISR) team released the Version 23 (V23) 4.4-km Aerosol Optical Depth (AOD) product, which has better spatial resolution than V22 at 17.6 km. However, its quality has not been validated in China. Here, V23 products for different spatiotemporal domains are obtained for validation against Aerosol Robotic NETwork (AERONET) AOD measurements for 29 sites from 2008 to 2017. Based on the national daily mean, V23 AOD yields a correlation coefficient (R) of 0.902 with AERONET; 59.45% of retrievals fall within the expected error (=EE; ±0.05 or ±0.2×AOD). A mean error (ME) of −0.0605 with 24.11% of retrievals falling below the EE indicates that MISR data are still underestimated at high AODs. The sample numbers and accuracies of spatially averaged 17.6-km and 50-km data are greatly improved relative to V22. The seasonal mean of V23 retrievals = EE in fall and winter are highest, followed by those in summer and spring; the validation results at 17.6 km are generally better than those at 50 km. By region, V23 retrievals = EE in the Beijing–Tianjin–Hebei (BTH), Yangtze River Delta (YRD) and Pearl River Delta (PRD) regions are 68.87%, 61.43%, and 73.13% respectively, while that of Taiwan is below 60% (55.75%). No V22 records exist in PRD, and V23 products over other regions in all seasons perform well; V22 retrievals in summer are also recommended. Compared with Terra/MODIS 3-km AOD in 2016, the V23 product has a slightly higher R value (0.925) with AERONET than MODIS (0.909). The MISR AOD bias is lower, and MODIS AOD is overestimated relative to the ground truth; both present consistent seasonality characteristics (spring > winter > summer > autumn), with the maximum in March and minimum in August. To investigate the spatiotemporal characteristics over long-term AOD, MISR V23 4.4-km AOD can be used in combination with other observation data.

Arctic aerosol-climate interactions are controlled by multiple factors including sources, processes and removal mechanisms of particles. The Arctic is mostly ocean, surrounded by mostly land, and our understanding of Arctic aerosol processes is incomplete due to scarce measurements carried out in sea ice regions. In particular, it is currently not known if these particular regions are sources of aerosols of primary or secondary origin. We present new results from ship-based measurements illustrating that marine new particle production and growth events occur in open ocean and melting sea ice regions in the Chukchi and East Siberian Seas. We report two new particle formation events during which a recently formed nucleation mode (<15 nm diameter) is detected and is observed to slowly grow into an Aitken mode (0.1–3.8 nm h−1). Our results suggest that new particle formation occurs in the marine boundary layer contributing to the Arctic aerosol population in the study region for the first time studied and herein reported.

Haze is a phenomenon caused by suspension of fine particulate matters in the air that leads to impaired visibility. In the meteorological practice, a haze day is determined using the observation of visibility and relative humidity, after screening the special weather days of rain, snow, dust, fog and others. While in the environmental monitoring practice and relevant studies, the term haze is also commonly used and a haze day is determined using the reading of particulate matters (PM). This has actually caused two different kinds of haze day, i.e., meteorological haze days (MHDs) and environmental haze days (EHDs), each with different definition and standard. Our analysis shows that although MHDs and EHDs overlap, the proportion of MHDs in EHDS is 43% in Beijing, 44% in Shanghai, and 46% in Guangzhou. Meanwhile, there are large percentage of MHDs that are not EHDs, about 21% in Beijing, 42% in Shanghai and 67% in Guangzhou. Therefore, an explicit distinction of the two haze definitions should be made in the study of PM pollution variation and cause in China, which will have important applications in addressing air pollution, formulating environmental policy, and dealing with health effect of haze in China.

Particulate matter (PM) pollution poses a huge public health threat, and exposure to haze pollution for short or long periods of time cause health problems. In this study, 16S rDNA and ITS high-throughput sequencing were used to analyze the microbial components of fine particulate matter (PM2.5) collected between December 20th and December 27th of 2016 during a severe haze in Tai'an, China. Although most inhalable microorganisms are not pathogenic to humans, we detected the presence of some types of bacteria that cause respiratory inflammation (such as Pseudomonas and Corynebacterium), allergic reactions (such as Alternaria), and lung inflammation (such as Nesterenkonia). Acute and chronic haze PM2.5 exposure experiments were conducted using BALB/c mice to gain insight about the harm these microbes may have on human health. Results indicate that acute exposure to haze PM2.5 can cause pathological lung damage, decrease the expressions of oxidative stress indicators T-AOC, SOD, and GSH-PX, increase the expression of MDA, and induce apoptosis. Furthermore, chronic exposure was found to cause more damage. Toll-like receptors can be used identify molecular patterns associated with microbial pathogens. The expression of TLR2 and TLR4 were increased in both single- and repeated-exposure groups, but they were significantly increased in the repeated-exposure group (P < 0.05). The role of biological components in PM in mediating inflammation and pathological damage should not be neglected.

Primary organic aerosol (POA) in diesel exhaust is semi-volatile and partitions mass between the gas and particle phases. POA volatility is not well understood for alternative fuels, varying engine loads, and for engines that feature modern emissions controls. In this study, we performed filter-based measurements of diesel exhaust from a modern-day non-road diesel engine for two different fuels (conventional diesel and soy-based biodiesel), two different engine loads (idle and 50% load), and with and without an emissions control device. Filters were analyzed offline to determine the POA volatility in two different ways: positive artifact on quartz filters at varying dilution ratios and speciation of alkanes. The POA volatility determined from our data suggests that POA mass emissions from diesel exhaust may be reduced by a factor of five with dilution to atmospherically relevant concentrations. These results are generally consistent with previous literature on POA volatility from non-road diesel engines but not with that from on-road diesel vehicles. POA volatility may hence need to be treated separately for non- and on-road sources in atmospheric models. Surprisingly, the POA volatility did not appear to vary under different combinations of fuel, engine load, and emissions control experiments performed, suggesting that POA might be dominated by unburned lubricating oil and its oxidation products. The POA volatility estimated from the speciation of alkanes was found to agree well with that determined from the dilution experiments. A kinetic model was used to calculate the gas/particle partitioning of POA in the dilution system. The modeling suggests that residence times in the dilution tunnel need to be on the order of minutes to allow the POA in the diluted exhaust to achieve gas/particle equilibrium. The use of short residence times (less than tens of seconds), similar to those used in conventional dilution systems, may bias the measurement of POA mass emissions in such systems and is of particular concern for emissions from cleaner, more modern combustion sources. The precise magnitude and direction of the bias depends on the exhaust temperature before dilution, tailpipe seed concentrations, dilution ratio, and residence times in the dilution tunnel. We recommend that kinetic models such as those used in this work be used, instead of using equilibrium assumptions, to inform the design and operation of the dilution tunnels as well to interpret the POA volatility from measurements made with those dilution tunnels.

This contribution compares 3-hourly estimates of aerosol optical depth at 550 nm (AOD550) and Ångström exponent (AE) from two similar reanalysis models, ECMWF's CAMS and NASA's MERRA-2, to reference remote-sensed observations from the worldwide AERONET network during the period 2003–2017. All data points are first subjected to a thorough quality assessment analysis. All valid AOD550 reanalysis estimates are also corrected to account for the difference in elevation between the nominal grid cell size (0.5 × 0.625°) and the reference AERONET ground station. Comparative results are obtained both on a continental basis and on climate disaggregation basis using the Köppen-Geiger (KG) classification. Based on 793 AERONET stations and ≈1.8 million valid 3-h data points, it is found that CAMS and MERRA-2 behave relatively similarly, with however some regional differences, depending on continent or KG class. AOD550's root-mean-square error (RMSE) varies in the range 0.031–0.268 for CAMS and 0.017–0.232 for MERRA-2, depending on continent. Globally, MERRA-2 performs better than CAMS, achieving an RMSE of 0.126, as compared to 0.144 for CAMS. In contrast, the two reanalyses have very similar overall RMSEs for AE, i.e., 0.382 for CAMS and 0.378 for MERRA-2. For local or regional studies, these results allow users to select the best possible source of data. For global studies, both aerosol products are found appropriate, albeit with different statistical properties.

Northeast British Columbia (BC) Canada, is a region in which natural gas production has undergone rapid development since 2007. We used nitrogen dioxide (NO2) and sulphur dioxide (SO2) data products of the Ozone Monitoring Instrument (OMI) to assess the impact of natural gas development activity on air quality in this region from 2005 to 2018. We noticed that values of both pollutants were elevated in the immediate vicinity of large emission sources within the Montney formation and Horn River Basin – regions, which have experienced an increase in unconventional natural gas activities. Places with elevated NO2 Vertical Column Densities (VCDs) are Fort St. John, Taylor, and Dawson Creek located in the Montney formation, and higher SO2 VCDs are found near the Fort Nelson gas plant situated in the Horn River and Liard Basin areas. Although all the OMI data products consistently reported relatively high NO2 VCDs in the same areas, VCD values vary substantially with data products largely due to differences in Air Mass Factor (AMF) calculations. The rate of increase in NO2 VCDs and mass between 2005 and 2018 in the Dawson Creek area was assessed at 2.34% yr−1 and 4.32% yr−1, respectively, and these rates of change are statistically significant. Although we obtained an overall increasing trend for NO2 in Northeast BC, we also noticed a decreasing trend in the period of 2011–2013, which may be attributed, in part, to compliance and enforcement of regulations concerning flaring activities from oil and gas activities in Northeast BC, or due to less development activities. From our analysis, we suggest that the current air quality monitoring network in Northeast BC should be expanded to capture the spatial distribution of SO2 by deploying one additional station near Fort Nelson equipped with meteorology and SO2 monitoring systems.

In this review, all available data on the effects of supersaturation in human airways were summarized and analysed, and the most critical parameters identified. The analysis shows the boundary conditions for increased supersaturation in airways: inhalation of cold air of T < 22 °C or cool saturated air of T < 25–27 °C. Thus, it was summarized for the first time that conditions during rainy weather or cold seasons in a temperate climate and rainy seasons in subtropical and tropical climates can induce supersaturated conditions in human airways. It was shown that under such conditions a total deposition of 300 nm particles may increase from ∼13% (when the supersaturation is not taken into account) to ∼90% due to enhanced condensational growth. It was found that such unusually high underestimation of deposition efficiency may be typical for most classical studies and approaches. An important observation was made for the first time: weather conditions which are favorable for enhanced deposition of submicron aerosols (and infectious aerosols) due to supersaturation in human airways may be connected with increased respiratory symptoms of asthma and chronic obstructive pulmonary disease (COPD) and two different patterns of seasonality of respiratory infections and influenza. This is one of the main aspects of this work that needs to be studied in the future. The primary implication of the results of this review is that weather patterns can play a significantly more important role in the deposition of ambient submicron aerosols in human airways than previously assumed.

Land use regression models (LUR) associate observed air pollution concentrations with surrounding land use characteristics for air pollution modelling. This technique is common in urban landscapes focused at a city-wide spatial scale. Our study tested the applicability of LUR modelling at a local scale, defined as multiple air monitors within a neighbourhood. The study area was 15.4 km of an urban transportation corridor in Mississauga, Canada. Nitrogen dioxide (NO2) was sampled at 112 sites during the summer in 2018 and observations ranged from 5.8 ppb to 19.65 ppb. A linear regression LUR model explained 69% of the variation in NO2 concentrations at this local scale, with estimated prediction errors less than 1.61 ppb, which were calculated by three cross-validation methods. Traffic volume, major and minor road lengths were key determinants among the predictor variables, and park area and distance to the nearest major intersection were the only variables with negative coefficients in the local-scale model. Extending the linear model approach with regression kriging improved the model's explanatory ability with a coefficient of determination at 0.91; however, smaller improvements were observed during cross-validation. Leave-one-out cross-validation for the linear model LUR model (RMSE = 1.44 ppb and a R2 = 0.64) and the regression kriging LUR model (RMSE = 1.34 ppb and a R2 = 0.69) were similar. Model performance remained stable when 10-fold cross-validation was performed with the regression kriging LUR model (regression kriging, R2 = 0.68 and RMSE = 1.36 ppb). The predicted air pollution levels ranged from 4.5 ppb to 25.6 ppb. This study demonstrates the ability of LUR modelling to perform well for local scale modelling in transportation dominated local urban environments.

SO42−, NO3− and NH4+ (SNA) are the major components of particulate matter in Beijing. In this study, hourly concentrations of SNA in PM1 were measured through an Aerodyne Aerosol Chemical Speciation Monitor (ACSM) at an urban site of Beijing, from February 3rd to 20th of 2017. The analysis of the differences between two pollution cases during the sampling period was further conducted. The results showed that the concentrations of NO3−, SO42− and NH4+ were 38.9 ± 10.5 μg/m3, 41.9 ± 22.2 μg/m3 and 31.3 ± 10.6 μg/m3 respectively in the first case. A negative correlation was reflected between the PM2.5 concentrations and the following two ratios: 1) NO3−/SO42−; 2) [NH4+] to ([NO3−]+2[SO42−]), with a correlation coefficient of −0.92 and −0.76 respectively. In the second case, the PM2.5 concentrations (proportions) were much higher, with values of 49.9 ± 17.0 μg/m3 (22.9 ± 7.7%), 42.3 ± 15.8 μg/m3 (20.3 ± 7.2%) and 33.1 ± 10.1 μg/m3 (15.3 ± 4.3%). In contrast. The two ratios were positively correlated with the PM2.5 concentrations, along with the correlation coefficient of 0.77 and 0.62. Hence, it is palpable that two pollution cases were sulfate and nitrate dominant in respective. The emission characteristics due to the Chinese Spring Festival before P1 might be a major cause. A modeling-monitoring coupled approach was established for the recognition of the secondary conversion of SO42− and NO3−. Results showed that sulfate/nitrate aged ratio (SAR and NAR) and sulfur oxidation ratio (SOR) in the second case were 0.48 ± 0.23, 0.22 ± 0.07 and 0.38 ± 0.23. They were all higher than those of the first case whose values were 0.32 ± 0.15, 0.18 ± 0.05 and 0.22 ± 0.12, which indicated that secondary conversion of precursors was enhanced in the second case. Although the OH concentrations were of no obvious difference in both cases, the average concentrations of H2O2, NO2 and the relative humidity were much higher in the second case, which provided sufficient conditions and time for the formation of SO42− and NO3−.

The climatological characteristics of biomass burning over the western Indo-Gangatic Plain (IGP) are examined during the post-monsoon (October-November) season from 2001-2018 using the Moderate resolution Imaging Spectrometer (MODIS) fire products. The intensity of the biomass burning are estimated from the fire pixels detected by the MODIS satellites in the form of fire counts, surface brightness temperature, and fire radiative power. Such biomass burning are mostly affected over Lahore and Patiala region of the western IGP. These fire products are examined along with optical and physical properties of aerosols and its radiative forcing estimated from AErosol RObotic NETwork (AERONET) data. Due to non-availability of long-term aerosol data, the study was performed only at Lahore (AERONET) and Patiala (MODIS) of the western IGP region. The current study shows increasing trends of average brightness temperature by 16% year−1 over Patiala and 14% year−1 over Lahore, which enhances the aerosol optical depth (AOD) by 3%–7% year−1 over the study region. The sphericity of the fine-mode aerosols are rising from 23% to 61% during non-fire to fire events and the dominance of fine-mode aerosols are observed during the active fire events. Further, the absorptivity of AOD (440 nm) has enhanced from 0.07 to 0.14 during non-fire to fire events. Asymmetric parameter (AS) of fine-mode aerosol increases from 0.65 to 0.68 during non-fire to active fire events. The characteristics of elevated aerosol layers due to the active fire events are clearly distinguished from the non-fire events within 0-2 km above the surface as noticed from high aerosol extinction and attenuated back scatter coefficients, obtained from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). Absorbing aerosols associated from biomass-burning contribute to the surface radiative forcing by -173.96 ± 47 Wm−2 and atmospheric forcing by 123.57 ± 41 Wm−2 over Lahore. The impact of the biomass-burning over Lahore has making the atmosphere more warming by 3.50 ± 1.14 K/Day. The estimated heating rates (HR) in the atmosphere are rising during both fire and non-fire events by 3.79% and 3.44% per year, respectively.

Chlorine radical plays an important role in ozone formation. However, it has not generally been included in air quality modelling in China. In this study, an emission inventory for atomic chlorine precursors was developed for Shanghai in the year 2017. Total emissions of chlorine radical precursors were estimated at 16,200.9 tons/year. The main source sectors of chlorine precursors in Shanghai include the volatilization of disinfectants, including in water treatment (8,400 tons/year, accounting for 52% among total emissions), in cooling towers (4,000tons/year, 25%), in wastewater treatment (2,700 tons/year, 17%), in tap water (310 tons/year, 2%), in swimming pools (280 tons/year, 2%), and in the usage of chlorine-containing disinfectants (210 tons/year, 1%). The contribution of sea salt heterogeneous reactions with ozone to chlorine radical precursors is estimated as 90 tons/year; this represents a lower bound on the emissions from sea salt because of other reaction pathways (e.g., the reaction of particulate chloride with N2O5). Local emissions from coal combustion and chemical manufacturing were estimated to be relatively small. This study provides a basis for further study regarding the influence of chlorine chemistry on ozone formation in Shanghai.

The recently developed Ion and Mass Balance (IMB) source apportionment methodology was applied to a traffic influenced urban aerosol, permitting the quantification of the contributions of 11 source components, or formation processes, which accounted for more than 96% of the measured aerosol mass loading. Main sources included exhaust and non-exhaust road vehicle emissions, biomass burning, secondary inorganic and organic pollutants, and primary soil and sea salt emissions. While in summer secondary carbonaceous matter is the predominant fraction, in winter biomass burning accounts, on average, for more than 40% of the PM2.5 aerosol. Comparison with Positive Matrix Factorization (PMF) showed the complementary characteristics of the two methodologies. PMF yielded 8 source profiles, including industry and oil combustion sources not discriminated by IMB. PMF is better at quantifying multiple component contributions to sources. IMB solves problems of collinearity between aerosol tracers and permits the discrimination of secondary formed pollutants.

The global long-term Climate Data Records (CDRs) of atmospheric SO2 and NO2 have been obtained from multiple satellite sensors since 1990s, and all these CDRs show consistently decreasing trends in developed countries and increasing trends in developing countries prior to 2010. However, much less clear is the quantitative differences among these CDRs and how such differences affect the inferences for atmospheric SO2 and NO2 climatology in terms of their annual means as well as their frequency distributions. Here, we compare and contrast the CDRs from the aged OMI sensor (the flagship for measuring NO2 and SO2 since 2005) and the young OMPS sensor series (that started measuring NO2 and SO2 in 2012 and will continue in next 2-3 decades). We show that after 2012, the difference of average SO2 between OMPS and OMI is 0.12 DU and it only decreases to 0.04 DU after bias correction, despite their consistence in spatial pattern. NO2 CDRs from OMPS and OMI overall exhibit general agreement in both magnitude and spatial pattern between. Furthermore, the CDR differences can lead to the opposite trend signs in developed countries and the difficulty to reconcile trend magnitude in developing countries. Notable consistence in trend signs does exist, regardless of radiative cloud fraction, mainly showing decline of SO2 and NO2 in China and increasing in Indian; much inconsistence is, however, found in many parts of developed countries. No SO2 trends and inconsistent NO2 trends are found over Europe, and notable differences are found over U.S. where OMI SO2 and NO2's declining trends are consistent with surface observations, but OMPS SO2, albeit its better spatial agreement with surface data, shows increasing trend. This study calls the importance to assess CDRs from different satellite sensors with the account of frequency distributions for extreme events. This importance is emergent as the atmospheric SO2 and NO2 amounts are closer to the uncertainties of satellite-based retrievals in developed countries and are or will be declining in developing countries in the coming decades, all of which make the detection of signs, magnitudes, and spatiotemporal dichotomy a challenge from space.