Biomass burning impacts on ambient aerosol at a background site in East China: Insights from a yearlong study

Biomass burning activities are ubiquitous in China. In order to better understand the biomass burning sources and their impacts on aerosol components in the background air of East China, biomass burning tracers, i.e., levoglucosan (LG), mannosan (MN) and non-sea-salt potassium (nss-K+) were quantified at the Lin'an site. The annual average concentrations of LG, MN and nss-K+ in PM2.5 were 0.13 ± 0.14 μg m−3, 0.009 ± 0.010 μg m−3 and 0.65 ± 0.38 μg m−3, respectively. The yearly variations of anhydrosugar tracers, i.e., LG and MN were fairly consistent, as well as nss-K+. However, due to extensive fireworks activity, nss-K+ was observed during a three-day episode from 7 to 9 February 2016 with abnormally high levels (average at 5.38 ± 3.55 μg m−3). The highest levels of biomass burning tracers were associated with the strong continental outflow from inland China in winter, while lower levels of biomass burning tracers were observed in the summer season, influenced by maritime air masses. Combined with the analysis of fire activity data, clear seasonal trends of biomass burning pollution in Lin'an are apparent, ranging from high to low in winter, spring, autumn and summer. By analyzing the LG/MN and LG/nss-K+ ratios, biomass burning aerosols in East China were identified to be predominately associated with burning of rice crop residues. Moreover, based on the relationship between biomass burning tracers and other components in aerosols, biomass burning plays an important role in regulating chemical properties of aerosols in background areas in East China, especially for carbonaceous components.