Characteristics of air pollution episodes influenced by biomass burning pollution in Shanghai, China

In the atmosphere, biomass burning can interact with other pollution sources and thereby aggravate air pollution. However, its influences on the occurrence and development of air pollution remain poorly understood. In this study, the characteristics of air pollution episodes influenced by biomass burning was investigated based on the field observation in Shanghai from 2014 to 2016. Results indicated that the fine particle pollution was serious during the whole observation period, and the high particulate pollution episodes mostly occurred in winter and spring. Four studied cases indicated that the ways to initiate high air pollution episodes were diverse, including local pollution sources, external transport and combined interaction of multiple pollution sources. All four high air pollution episodes behaved high K+, CO and NH3 concentrations, showing the existence of biomass burning pollution. And most of biomass burning pollution were from northwest China and some provinces in east and southeast China, which had active biomass burning activities. In the high pollution episodes, secondary inorganic aerosols (SIA) accounted for a large proportion of PM2.5, but SIA did not always initiate high pollution episodes. The high concentrations of sulfate and nitrate aerosols brought by the transport of biomass burning could also induce the occurrence of high pollution episodes. Also, the mixing of biomass burning plumes with other pollution sources could enhance SIA formation and aggravate air pollution. This study highlights the significant roles of biomass burning in the occurrence and development of high air pollution.