Significant source of secondary aerosol: formation from gasoline evaporation emissions in the presence of SO 2 and NH 3

Abstract. Gasoline evaporation emissions have become an important anthropogenic source of urban atmospheric VOCs and secondary organic aerosol (SOA). These emissions have a significant impact on regional air quality, especially in China where car ownership is growing rapidly. However, the contribution of evaporation emissions on the secondary aerosol (SA) is not clear in air pollution complex in which high concentration of SO 2 and NH 3 was present. In this study, the effects of SO 2 and NH 3 on SA formation from unburned gasoline vapors were investigated in a 30 m 3 indoor smog chamber. It was found that increase in SO 2 and NH 3 concentrations could promote linearly the formation of SA, which could be enhanced by a factor of 1.6–2.6 and 2.0–2.5, respectively. Sulfate was most sensitive to the SO 2 concentration, followed by organic aerosol, which was due not only to the well-known acid catalytic effect, but also related to the formation of organic sulfur-containing compounds. In the case of increasing NH 3 concentration, ammonium nitrate increased more significantly than organic aerosol, and nitrogen-containing organics were also enhanced, as revealed by the results of positive matrix factorization (PMF) analysis. Meanwhile, new particle formation (NPF) and particle size growth were significantly enhanced in the presence of SO 2 and NH 3 . This work indicates that gasoline evaporation emissions will be a significant source of SA, especially in the presence of high concentrations of SO 2 and NH 3 . Meanwhile, these emissions might also be a potential source of sulfur- and nitrogen-containing organics. Our work provides a scientific basis for the synergistic emission reduction of secondary aerosol precursors, including NO x , SO 2 , NH 3 and particularly VOCs, to mitigate PM pollution in China.