Aqueous production of sulfur-containing aerosols from nitroaromatic compounds and SO2 in wintertime urban haze.

Nighttime aqueous oxidation of fossil fuel emissions is a significant source of atmospheric secondary organic aerosols. However, the underlying mechanism of the aqueous processing remains unclear. Utilizing ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry of water-soluble organic carbon samples, we present field observations that reveal the aqueous-phase conversion of nitroaromatic compounds (NACs) and sulfur-containing aerosols from fossil fuel combustion at high relative humidity during a severe haze event in Beijing in the winter of 2016. We have confirmed that the ring-breaking oxidation of NACs can generate nitrous acid in the aqueous phase, which rapidly oxidizes sulfur dioxide (SO2) to sulfate. Subsequently, reactions between sulfate and unsaturated compounds contribute to the formation of aliphatic organosulfates. Our results elucidate a molecular-level understanding of the aqueous production of sulfur-containing aerosols from NACs and SO2 in wintertime urban haze.