Chemical composition and sources of submicron aerosols in winter at a regional site in Beijing-Tianjin-Hebei region: Implications for the Joint Action Plan.

The Ministry of Environmental Protection released a Joint Action Plan for Control of Air Pollution (Hereafter, Joint Action Plan, JAP), to reduce PM concentrations in the Beijing-Tianjin-Hebei region (BTH) during the winter of 2017. To investigate the effectiveness of the controls, we deployed an aerosol chemical speciation monitor and collected filter samples at Xianghe, a representative site for the BTH, to characterize the aerosol composition during the implementation of the JAP. Those results were compared with earlier data obtained from a literature survey and reanalysis of studies in the BTH. During several pollution episodes in the control period, the major aerosol types changed relative to the earlier studies from sulfate, oxygenated organic aerosol, and coal combustion organic aerosol to nitrate and biomass burning organic aerosol. The dominant secondary inorganic aerosol species during the JAP changed from sulfate to nitrate, and the main source for primary organic aerosol switched from coal combustion to biomass burning. These changes can be explained by the fact that the JAP controls targeted coal combustion and SO but not biomass burning or NO emissions. Our evaluation of the control measures provides a scientific basis for developing new policies in the future.