Elsevier

Atmospheric Environment

Volume 224, 1 March 2020, 117312
Atmospheric Environment

Impact of control measures and typhoon weather on characteristics and formation of PM2.5 during the 2016 G20 summit in China

https://doi.org/10.1016/j.atmosenv.2020.117312Get rights and content

Highlights

  • Hourly PM2.5, WSII, and BC were measured under control measures and typhoon.

  • High PM2.5 under control measures due to stagnant weather and transport.

  • Stagnant weather with high RH was beneficial for formation of SO2 to sulphate.

  • Sea salt brought by typhoon favored nitrate formation even under low NO2.

Abstract

The implementation of strict emission control during the G20 summit in China and the occurrence of Typhoon Malarkas in September 2016 provided a valuable opportunity to examine the role of control measures and special weather condition in the formation of PM2.5. Water-soluble inorganic ions (WSII) were measured hourly in addition to PM2.5 mass concentration and black carbon (BC) and gaseous pollutants in Ningbo located in the Yangtze River Delta (YRD) region of China. Three distinct cases, i.e., a control case, a normal case, and a typhoon case, were investigated during the study period. PM2.5 was higher in the control case (37.5 μg m−3) than in the normal case (29.8 μg m−3), whereas the lowest PM2.5 (14.2 μg m−3) was observed in the typhoon case. The analyses of meteorology and backward trajectory suggested that stable weather and regional transport from inland regions accounted for the high PM2.5 under strict control. Only the concentrations of Ca2+ and NO3 decreased in the control case, while those of all water-soluble inorganic components (except Na+ and Mg2+) decreased substantially in the typhoon case. SO42− dominated the WSII, with the highest contribution, 62%, in the control case. This result was attributed to a stagnant atmosphere with a high relative humidity (RH), which was beneficial for the transformation of SO2 to SO42−. The control and typhoon cases both resulted in extremely low NO2, but the contribution of NO3 to PM2.5 was reduced in the control case and increased in the typhoon case. The close correlation of the NOR (nitrate oxidation ratio) with Na+ and Mg2+ in the typhoon case was indicative of sea salt associated with the typhoon which provided a surface for the heterogeneous formation of NO3. The presented results facilitate a better understanding of the characteristics and formation of PM2.5 under the influence of artificial control and natural intervention.

Introduction

Atmospheric PM2.5 (particulate matter with a dynamic equivalent diameter less than 2.5 μm) pollution is influenced by many factors. Fine particles can be directly released into the atmosphere by anthropogenic and natural activities. They can be subsequently transformed from primary pollutants (such as sulphur dioxide (SO2) and nitrogen oxides (NOX)) (Gard et al., 1998; George et al., 2015; Zhang et al., 2015). Huang et al. (2012) presented three typical kinds of air pollution in Shanghai: secondary pollution episode, dust pollution episode, and biomass combustion pollution episode with PM2.5 dominated by secondary aerosols, minerals, and K+ and carbonaceous aerosol, respectively. Fu et al. (2008) and Wang et al. (2006) determined that the heterogeneous reactions from SO2 and NO2 to SO42− and NO3 plays an important role in the formation of PM2.5. Except for the chemical factors, previous studies have also reported on the conducive effects of regional transport, relative humidity (RH), and stagnant meteorological conditions on the formation of PM2.5 (Wang et al., 2018; Li et al., 2017b). Overall, the formation mechanism of PM2.5 in the atmosphere is related to the emission sources, meteorological conditions, and transport of pollutants (Sun et al., 2006; Fu et al., 2008; Huang et al., 2012; Li et al., 2015; Zhang et al., 2015; Hua et al., 2016; Han et al., 2016a).

China is still under tremendous threat of PM2.5 pollution (Huang et al., 2012; Ming et al., 2017). The Chinese government has implemented the “Atmospheric Pollution Prevention and Control Action” in recent years with the aim of relieving air pollution in China. Moreover, the effects of the control measures on the reduction of pollution have been obvious during major events such as the Beijing 2008 Olympic Games, the 2014 Asia-Pacific Economic Cooperation (APEC) summit, and the China Victory Day Parade (V-Day Parade) in 2015 (Sun et al., 2016; Xu et al., 2017; Liang et al., 2017). A series studies have been conducted on the major species (element, water-soluble ions, and BC) of PM during the 2008 Olympic Games, and the results showed that the emission mitigation measures had successful reduction for the pollutants (Schleicher et al., 2011, 2012; Li et al., 2012). The obvious reduction of PM2.5 composition also found under the strict emission control of the V-Day Parade in 2015 comparing to the same period of a few years earlier (Han et al., 2016b). Although the emission restriction policy resulted in the suppression of PM, some secondary pollution episodes formed via the photochemical reaction and regional transport still could happen. In the early control period of the Olympic Games, a vehicle emissions and coal combustion were achieved, but the formation of secondary aerosol in regional scales still increased (Sun et al., 2011, 2016; Wang et al., 2010).

As for the possibilities of the pollution episodes even under the emission control period, it is important to understand the formation mechanism of PM2.5 to better regulate air quality. However, some special weather conditions also have a significant impact on the formation and mitigation of pollutants (Yan et al., 2016; Wang et al., 2005a). For example, typhoons are the predominant weather conditions during the summer monsoon season in East Asian. Fang et al. (2009) determined that typhoons re-suspended dust and caused an increase of particles (Fang et al., 2009). Meanwhile, the special meteorological conditions caused by a typhoon such as heavy rainfall and active atmospheric movement, could decrease atmospheric pollutants and affect the formation mechanism of PM2.5 (Yan et al., 2016; Fang et al., 2009). Control measures and typhoon both significantly reduce the concentration of atmospheric primary pollutants. Nevertheless, there are few comparative studies on the roles they play in the formation mechanism of PM2.5.

The 2016 G20 summit was held on 4–5 September 2016 at Hangzhou, the Yangtze River Delta (YRD) region of China. To improve air quality, control measures such as the closure of industrial plants with high emission, cessation of construction activities, and the restriction of traffic flow, were adopted by the government in the YRD region from the middle of August until the summit ended. According to the distance from the main stadium, the YRD region was divided into core control zone, strict control zone, and normal control zone. The adjacent provinces (such as Shanghai, Jiangsu, Anhui) also implemented some mitigation measures to ensure the air quality. Ningbo, as a city adjoined Hangzhou, was part of the strict control zone. During the G20 summit, the government reduced the emission of pollutants by controlling or prohibiting industrial, construction, and traffic activity in the YRD region. After the G20 summit, it was determined that typhoon Malarks had a significant influence on the YRD region, especially the coastal cities in the YRD region. Therefore, the strict control measures and typhoon occurred within a short period (September 2016) and offers a valuable opportunity to study the difference in the formation mechanism of PM2.5. Several studies have reported the air quality in Hangzhou under the emission control of the 2016 G20 summit. Li et al., (2017c) had found the high reduction of particulate matter in Hangzhou during the control period of G20 summit compared to the period previous to the G20 summit. Li et al., (2017d) found the night time transport of pollutants was unfavourable for the mitigation of pollutants in Hangzhou even under the strict emission control of the G20 summit. However, few studies were focused on the comparison of different formation mechanism of secondary inorganic aerosols influenced by the control measures and the typhoon weather. This study aims to: (1) differentiate between the characteristics of PM2.5 and the gaseous pollutants that are affected by the control measures and typhoon weather; (2) elucidate the influence of meteorological conditions on the water-soluble inorganic components of PM2.5; (3) investigate the formation mechanism of secondary inorganic aerosols under control measures and typhoon weather.

Section snippets

Description of the sampling site

The observations campaign was conducted on the rooftop of the Ningbo Urban Environment Observation and Research Station (NUEORS) building (29.87° N, 121.91° E, 10 m a.s.l), located in the Beilun District of Ningbo in the YRD region, China (Fig. 1). NUEORS is a suburban site that is 20 m away from the coastline and approximately 172 km northwest from the host city of the 2016 G20 summit. Southeast of the sampling site is a park, northeast is a residential area, while in the southwest and

General characteristics of PM2.5 and the gaseous pollutants

As shown in Fig. 2, the mean hourly concentration of PM2.5 at NUEORS during the observation period was 23.6 ± 12.0 μg m−3 with a range of 1.0–54.0 μg m−3. The temporal distribution of the gaseous pollutants is similar to that of PM2.5. Three cases were investigated during the observation period. Case 1 (0:00 1 September – 12:00 4 September) was influenced by the strict control measures implemented during the G20 summit. The emission reductions for industry, power plant, residential, and

Formation mechanism of PM2.5

The three cases occurred under different meteorological conditions and exhibited different chemical characteristics. This study attempted to explore the formation mechanism of PM2.5, particularly, with regard to the secondary inorganic components, with respect to the distinct meteorological conditions of the three cases.

Conclusions

In this study, we characterized the water-soluble inorganic chemical components and BC of PM2.5 and discussed the formation of SIA with the influence of the strict control measures and a typhoon in Ningbo during September 2016. The mean concentrations of PM2.5 were 37.48, 29.84, and 14.24 μg m−3 in the control case, normal case, and typhoon case, respectively. The effect of mitigation measures on PM2.5 concentration was far offset by the influence of stable weather and regional transport in the

CRediT authorship contribution statement

Yanru Zhang: Conceptualization, Methodology, Software, Investigation, Writing - review & editing. Zhenyu Hong: Methodology, Software, Writing - original draft. Jinsheng Chen: Conceptualization, Supervision, Writing - review & editing. Lingling Xu: Conceptualization, Writing - review & editing. Youwei Hong: Writing - original draft. Mengren Li: Writing - original draft. Hongfei Hao: Investigation, Writing - original draft. Yanting Chen: Investigation. Yuqing Qiu: Investigation. Xin Wu:

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This study was funded by the National Key Research and Development Program (2016YFC02005 & 2016YFE0112200), the National Natural Science Foundation of China (41575146), the Chinese Academy of Sciences Interdisciplinary Innovation Team Project, and the Natural Science Foundation of Fujian Province, China (2016J01201).

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