Spatial and temporal variability of PM2.5 and PM10 over the North China Plain and the Yangtze River Delta, China
Introduction
Along with the rapid economic growth and urbanization, China has been experiencing severe particulate matter (PM) pollution problem, especially in the most developed regions, such as the North China Plain (NCP), the Yangtze River Delta region (YRD), and the Pearl River Delta region (PRD) (van Donkelaar et al., 2010). Annual average concentrations of particles with aerodynamic diameter equal to or less than 2.5 μm (PM2.5) were observed over 100 μg/m3 in Beijing (He et al., 2001) and 60 μg/m3 in Shanghai (Ye et al., 2003), greatly exceeding the World Health Organization (WHO) guideline value of 10 μg/m3 (WHO, 2005). An increasing trend in the severity and frequency of PM pollution in more recent years has been observed (Deng et al., 2008, Li et al., 2013, Zhang et al., 2008, Zhao et al., 2013).
Sustained exposure to high PM air pollution level has significant health effects (Correia et al., 2013, Dockery, 2001, Dockery et al., 1993, Fann et al., 2012, Franklin et al., 2007, Ito et al., 2011, Ostro et al., 2006). According to the Global Burden of Disease Study, 3.2 million people died from air pollution in 2010 among which 1.2 million were from China (Lim et al., 2012). Half-a-billion people alive in northern China in the 1990s will live an average of 5.5 years less than their southern counterparts because of inhaling more polluted air generated from coal burning activities (Chen et al., 2013). Retrospective regression analysis of 80,515 deaths recorded at eight urban districts in Beijing between 2004 and 2008 showed an association between increased air pollution and increased years of life lost (Guo et al., 2013).
In the past decade, a remarkable effort has been made to investigate the characteristics, sources, mechanism and adverse health effects of PM pollution in China, mostly focusing on a few mega-cities, such as Beijing, Shanghai, and Guangzhou (Li et al., 2008, Li et al., 2011, Liu et al., 2008a, Liu et al., 2008b, Wang et al., 2014a, Wang et al., 2012, Wang et al., 2010, Zheng et al., 2009). Recent studies indicate that the spatial extent of PM pollution in these areas has been expanding to broader regional scales (Liu et al., 2013, Zhang et al., 2008). This trend urges needs for large-scale ambient PM monitoring for the purpose of designing effective control strategies.
Starting from June 2000, the government of China started publishing daily air pollution index (API) for a number of key cities (increased from 47 cities in 2000 to 120 cities in 2011), which was calculated based on ground monitoring of 24 h average concentrations of sulfur dioxide (SO2), nitrogen dioxide (NO2), and particulate matter with aerodynamic diameter equal to or less than 10 μm (PM10) (http://datacenter.mep.gov.cn/). PM2.5 was not included in this routine measurement and no PM2.5 standards were available. On February 29th, 2012, the third revision of the “Ambient Air Quality Standard” (AAQS) (BG3095-12) was released, and PM2.5 was adopted into the AAQS for the first time. The AAQS Grade I and Grade II standards are 35 and 75 μg/m3, respectively, for 24 h average PM2.5, and 50 and 150 μg/m3 for 24 h average PM10 (MEP, 2012a). In March 2012, the Chinese Ministry of Environmental Protection (MEP) released the official revisions of the ambient air quality index (AQI), which was calculated based on seven pollutants including SO2, NO2, PM2.5 PM10, carbon monoxide (CO), 1 h peak ozone (O3), and 8 h peak O3 (MEP, 2012b). In January 2013, more than 100 of Chinese major cities started releasing concentrations of these seven pollutants and calculated AQI values to the public based on all monitoring stations throughout each city (MEP, 2012a). These extensive air quality observation data are publicly accessible. By studying this rich dataset, we could improve our understanding of PM emission sources, its formation mechanisms, transport pathways, and potential causes of air quality degradation.
In this study, we analyzed the hourly and daily concentrations of six air pollutants (SO2, NO2, PM2.5, PM10, CO, 1 h O3 and 8 h O3) measured at 13 cities in the NCP region and 20 cities in the YRD region in summer 2013. The spatial and temporal variations of these pollutants were investigated. This study was motivated by a few reasons. First, high PM pollution have been reported in summer in the two regions. Second, many studies have been conducted in the literature to investigate the high PM pollution in winter and biomass burning seasons (for examples, Chen and Xie, 2014, Ding et al., 2013, Sun et al., 2014), but only limited studies which examined the annual variability of PM included some summer studies. Third, the previous studies on summer episodes are mostly limited to a small urban/regional scale (for examples, He et al., 2001, Peng et al., 2011, Sun et al., 2004b, Ye et al., 2003). The information of spatial and temporal variations of summer PM pollution in a broader regional scale is sparse in literature. This is the first attempt of charactering regional PM2.5 pollution using ground-measurement data with hourly time resolution across 33 cities in China.
Section snippets
Study areas
The NCP represents a geographically flat region in the northern part of Eastern China, including the municipalities of Beijing (the national capital) and Tianjin (an important industrial city and commercial port), most part of Hebei, Heinan, Shangdong provinces, and the northern part of Anhui and Jiangsu provinces, with an approximately 1/5 of the China total population (China, 2012). PM2.5 has been studied in Beijing and Tianjin for more than 10 years (Gao et al., 2011, Guo et al., 2012, He
Summertime air quality overview
Fig. 2 shows the concentrations of PM2.5 (a), PM10 (b), CO (c), SO2 (d), NO2 (e), and 8 h peak O3 (f) averaged over the entire study time period (June 1st–August 31st, 2013) for the 36 cities in the study area. Average PM2.5 concentrations in the NCP were high with an average concentration of over 70 μg/m3 in all cities except Qingdao. Excluding Qingdao, small difference in the average PM2.5 concentration was observed among cities, indicating small spatial gradients in PM2.5 in the NCP. The PM
Conclusion
PM concentration data in the NCP and the YRD regions in China between June 1st, 2013 and August 31st, 2013 were recorded at the air quality monitoring network of the Chinese Ministry of Environmental Protection. Our analysis shows that averaged PM2.5 concentrations at both regions exceeded the World Health Organization guideline values, indicating severe human exposure to ambient PM in the most developed and populated areas in China. The frequencies of occurrence of PM2.5 and PM10
Acknowledgement
The authors gratefully acknowledge Dr. Gong Zhang of National Aeronautics and Space Administration (NASA) Ames Research Center (ARC) for his support to this project. The authors gratefully acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model and/or READY website (http://www.ready.noaa.gov) used in this publication.
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