Response of aerosol composition to different emission scenarios in Beijing, China.

Understanding the response of aerosol chemistry to different emission scenarios is of great importance for air pollution mitigating strategies in megacities. Here we investigate the variations in air pollutants under three different emission scenarios, i.e., heating season, spring festival holiday and non-heating season using aerosol composition and gaseous measurements from 2 February to 1 April 2015 along with source apportionment and FLEXPART analysis in Beijing. Our results showed substantially different aerosol composition among three emission scenarios that is primarily caused by different emission sources. All aerosol and gas species showed ubiquitously higher concentrations in heating season than non-heating season with the largest enhancement for fossil OA (FOA) and chloride. On average, the particulate matter (PM) level in winter heating season can be enhanced by 70% due to coal combustion emissions. In contrast, cooking aerosols and traffic related species showed significant reductions as a response of reduced anthropogenic activities during the spring festival holiday, sulfate and secondary organic aerosol (SOA) however even increased due to enhanced aqueous-phase production. Such compensating effects resulted in small changes in PM levels for haze episodes during the holiday period despite reduced anthropogenic emissions. Our results have significant implications that local emission controls during winter severe pollution episodes can reduce primary aerosols substantially, but the mitigating effects can be significantly suppressed by enhanced secondary formation under stagnant meteorological conditions.