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Abstract
Abstract. The simultaneous observation and analysis of atmospheric fine particles (PM2.5) on a regional scale is an important approach to develop control strategies for haze pollution. In this study, samples of filtered PM2.5 were collected simultaneously at three urban sites (Beijing, Tianjin, and Shijiazhuang) and at a regional background site (Xinglong) in the Beijing–Tianjin–Hebei (BTH) region from June 2014 to April 2015. The PM2.5 at the four sites was mainly comprised of organic matter, secondary inorganic ions, and mineral dust. Positive matrix factorization (PMF) demonstrated that, on an annual basis, secondary inorganic aerosol was the largest PM2.5 source in this region, accounting for 29.2–40.5 % of the PM2.5 mass at the urban sites; the second-largest PM2.5 source was motor vehicle exhaust, particularly in Beijing (24.9 %), whereas coal combustion was also a large source in Tianjin (12.4 %) and Shijiazhuang (15.5 %), with particular dominance in winter. Secondary inorganic aerosol plays a vital role in the haze process, with the exception of the spring haze in Shijiazhuang and Tianjin, for which the dust source was crucial. In addition to secondary transformations, local direct emissions (coal combustion and motor vehicle exhaust) significantly contribute to the winter haze at the urban sites. Moreover, with the aggravation of haze pollution, the OC ∕ EC mass ratio of PM2.5 decreased considerably and the nitrate-rich secondary aerosol increased during all four seasons in Beijing, both of which indicate that local motor vehicle emissions significantly contribute to the severe haze episodes in Beijing. To assess the impacts of regional transport on haze pollution, the PMF results were further processed with backward-trajectory cluster analysis, revealing that haze pollution usually occurred when air masses originating from polluted industrial regions in the south prevailed and is characterized by high PM2.5 loadings with considerable contributions from secondary aerosols. This study suggests that control strategies to mitigate haze pollution in the BTH region should focus on the reduction of gaseous precursor emissions from fossil fuel combustion (motor vehicle emissions in Beijing and coal combustion in Tianjin, Hebei, and nearby provinces).
Highlights
Due to rapid economic development, rapid urbanization processes, and excessive energy consumption, regional haze pollution has been recognized as the most severe environmental problem in China and has received extensive attention from the government, the public, and scientists in recent years
Because the Beijing–Tianjin– Hebei (BTH) region features the strongest pollutant emissions (Zhao et al, 2012), unfavorable meteorological conditions (Cai et al, 2017; Xu et al, 2011), and a unique topography, extreme haze pollution characterized by high fine particulate matter (PM2.5) loading and very low visibility has frequently occurred in this region
48 h backward trajectories terminated at a height of 100 m above ground level were calculated for the four sampling sites using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT 4.9) model developed by the US National Oceanic and Atmospheric Administration Air Resources Laboratory (NOAA ARL)
Summary
Due to rapid economic development, rapid urbanization processes, and excessive energy consumption, regional haze pollution has been recognized as the most severe environmental problem in China and has received extensive attention from the government, the public, and scientists in recent years In terms of haze mitigation strategies, Guo et al (2014) suggested that regulatory controls on gaseous emissions for volatile organic compounds and nitrogen oxides from local transportation and sulfur dioxide from regional industrial sources are the keys to reducing the urban PM level in Beijing These studies were often conducted at single sites (mostly in Beijing) and/or for short periods (specific haze events or a certain season); long-term multisite studies are scarce (Li et al, 2017; Shen et al, 2016; Zhang et al, 2013; Zhao et al, 2013c; Zong et al, 2016). This study can provide an overall understanding of the regional signal of PM2.5 pollution in the BTH region and support stakeholders and policy makers in understanding the impacts of regional sources on high PM2.5 loadings, facilitating the design of effective joint emission abatement strategies
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