Simulations of Cloud and Aerosol-Phase Sulfate Formation Using GAMMA 6.0

Analysis of haze events under highly polluted conditions has indicated a gap in our understanding of the formation of particulate sulfate. In particular, air quality modeling studies inferred the importance of aerosol-phase S(IV) oxidation, which had previously received less attention than cloud water processes. Given the multitude of S(IV) oxidation pathways and their sensitivity to parameters such as ionic strength and pH, more data were needed before these processes could be incorporated into models. In the past decade laboratory studies have filled in this gap, with a proliferation of proposed mechanisms for sulfate formation in the aerosol phase and at the gas-aerosol interface.

We have updated the Gas Aerosol Model for Mechanism Analysis (GAMMA) to include updated S(IV) oxidation chemistry for cloudwater conditions following current recommendations (Tilgner et al. 2021), in addition to pH tracking and transition metal ion cycling. For aerosol conditions, we have implemented recently recommended mechanisms from the literature for S(IV) oxidation via HOOH, ROOH, NO2, TMI catalyzed processes and uncatalyzed oxidation, as well as updated organosulfate formation chemistry. Results will be presented for sensitivity studies performed under Beijing winter conditions, urban US, and rural conditions, and trends will be discussed.