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. © 2025 Science China Press.