Observational insights into the environmental effect for secondary inorganic aerosol formation in the Northeast China: Influence of biomass burning

Secondary inorganic aerosols (SIA), as one of the main ubiquitous components of PM2.5, still have unclear impacts on their formation in the ambient environment, especially under extremely cold weather conditions. To explore the effects of open biomass burning (OBB) source emissions and meteorological factors on SIA formation, biomass burning tracer, i.e., levoglucosan (LG), was observed along with SIA were analyzed during the heating season at the Longfengshan (LFS) background of Northeast China. Based on the LG/OC ratio and fire hotspots, the entire sampling campaign was divided into OBB and non-open biomass burning (NBB) periods. It was found that OBB emissions had little effect on sulfate formation but a significant impact on nitrate formation. High relative humidity (RH) conditions played a crucial role in SIA formation, with both SO42- /EC and NO3-/EC increasing as RH elevated at temperatures below -10 degrees C. Furthermore, the temperature dependence of SO42-/EC and NO3-/EC indicated that temperature could enhance the activity of either aqueous-phase production or gas-phase reactions, subsequently promoting the formation of SO42- and NO3- in the ambient environment. Additionally, positive matrix factorization (PMF) analysis was used to scientifically separate the sources of ambient aerosols during OBB and NBB periods.