Sulfate, nitrate and organic are the most important aerosol components at our site. Investigating the formation process of them together with other polluted gases is important not only for air pollution control but also for understanding the climate system. Although the mechanisms of secondary aerosol components have been widely studied, in situ observational evidence implicating an important formation pathway of different aerosol components in the real atmosphere has been rare.
For sulfate, Xie et al. (2015) report two unique cases implicating an important role of NO2 in SO2 oxidation, from an intensive campaign conducted at SORPES in East China, showing distinctly different mechanisms of sulfate formation by NO2 and related nitrogen chemistry. The first case occurred in an episode of mineral dust mixed with anthropogenic pollutants and especially high concentrations of NOx (Figure 1). It reveals that NO2 played an important role, not only in surface catalytic reactions of SO2 but also in dust-induced photochemical heterogeneous reactions of NO2, which produced additional sources of OH radicals to promote new particle formation and growth.
Figure 1 Time series of PM mass concentration, trace gases, particulate calcium, sulfate, aerosol size distributions, and meteorological parameters measured during case 1
Xie, Y.N., Ding, A.J., Nie, W., Mao, H.T., Qi, X.M., Huang, X., Xu, Z., Kerminen, V.-M, Petäjä, T., Chi, X.G., Virkkula, A., Boy, M., Xue, L.K, Guo, J., Sun, J.N., Yang, X.Q., Kulmala, M., and Fu, C.B.: Enhanced sulfate formation by nitrogen dioxide: Implications from in situ observations at the SORPES station, J. Geophys. Res. Atmos., 120, 12,679–12,694, 2015.