Exploring the inorganic and organic nitrate aerosol formation regimes at a suburban site on the North China Plain

Nitrate-driven aerosol pollution frequently occurs during winter over the North China Plain (NCP). Extensive studies have focused on inorganic nitrate formation, but few have focused on organic nitrates in China, preduding a thorough understanding of the nitrogen cycle and nitrate aerosol formation. Here, the inorganic (NO3,inorg) and organic nitrate (NO3,org) formation regimes under aerosol liquid water (ALW) and aerosol acidity (pH) influences were investigated during winter over the NCP based on data derived from an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The campaign-averaged concentration of the total nitrate was 53 mu g m(3), with a 13% contribution from NO3,org, which exhibited a significantly decreased contribution with increasing haze episode evolution. The diurnal cycles of NO3,inorg and NO3,org were similar, with high concentrations during the nighttime at a high ALW level, revealing the important role of aqueous-phase processes. However, the correlations between the aerosol pH and NO3,inorg (R-2 = 0.13, P < 0.01) and NO3,org (R-2 = 0.63, P < 0.01) during polluted periods indicated a contrasting effect of aerosol pH on inorganic and organic nitrate formation. Our results provide a useful reference for smog chamber studies and promote a better understanding of organic nitrate formation via a nthropogenic emissions. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study reveals that inorganic and organic nitrates in the North China Plain during winter are influenced by aerosol liquid water and aerosol acidity, with organic nitrates contributing less as haze episodes evolve. Additionally, the importance of aqueous-phase processes in nitrate formation and the contrasting effects of aerosol pH on inorganic and organic nitrate formation are highlighted in polluted periods.