Trends of surface PM2.5 over Beijing–Tianjin–Hebei in 2013–2015 and their causes: emission controls vs. meteorological conditions

Abstract

The PM2.5 (particulate matter with a diameter of less than 2.5 μm) trends during the period 2013–2015, in 13 cities over the Beijing–Tianjin–Hebei region, and their causes, were investigated using observations at 75 stations and a regional air quality model. It was found that annual PM2.5 in this region experienced a significant decrease in 2014 and 2015, compared with 2013. PM2.5 in 2015 almost met the target on air quality in the 13th Five-Year Plan (2012–2017). In southern cities (e.g. Xingtai, Handan, Shijiazhuang, and Cangzhou), this PM2.5 decreasing trend was caused by both meteorological conditions and regional emission controls in 2014 and 2015. Contributions from regional emission controls were more significant than meteorological conditions. In Tianjin and Langfang, the impact of regional emission controls was partly offset by the meteorological conditions in 2014. In 2015, meteorological conditions turned favorable for a PM2.5 decrease, but emission controls were still the dominant cause. Compared with polluted cities in Hebei and Tianjin, the decreasing trend in Beijing was small (4% and 9% in 2014 and 2015). This reflects the competition between adverse meteorological conditions and emission controls. In northern cities (Tangshan, Qinhuangdao, and Zhangjiakou), regional emission controls dominated the PM2.5 decreasing trend in 2014 and 2015, although they were partly offset by meteorological conditions. In all cities during the heating season in 2015, a more significant decreasing trend of high PM2.5 from emission controls was found than low and middle PM2.5. This indicates that air pollution controls are developing towards refined management (e.g. the Heavy Air Pollution Emergency Response Program) in this region.