Effects of NO2 and SO2 on the secondary organic aerosol formation from β-pinene photooxidation

Elucidating the effects of anthropogenic pollutants on the photooxidation of biogenic volatile organic compounds is crucial to understanding the fundamental mechanisms of secondary organic aerosol (SOA) formation. Here, the impacts of NO 2 and SO 2 on SOA formation from the photooxidation of a representative monoterpene , β -pinene, were investigated by a number of laboratory studies. The results indicated NO 2 enhanced the SOA mass concentrations and particle number concentrations under both low and high β -pinene conditions. This could be rationalized that the increased O 3 concentrations upon the NO x photolysis was helpful for the generation of more amounts of O 3 -oxidized products, which accelerated the SOA nucleation and growth. Combing with NO 2 , the promotion of the SOA yield by SO 2 was mainly reflected in the increase of mass concentration, which might be due to the elimination of the newly formed particles by the initially formed particles. The observed low oxidation degree of SOA might be attributed to the fast growth of SOA, resulting in the uptake of less oxygenated gas-phase species onto the particle phase. The present findings have important implications for SOA formation affected by anthropogenic–biogenic interactions in the ambient atmosphere.