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Investigating aqueous production pathways of particulate sulfur in CMAQ with AQCHEM-KMT (version 2) and the sulfur tracking method
Citation:
Fahey, K. AND S. Roselle. Investigating aqueous production pathways of particulate sulfur in CMAQ with AQCHEM-KMT (version 2) and the sulfur tracking method. 2019 Annual CMAS Conference, Chapel Hill, NC, October 21 - 23, 2019.
Impact/Purpose:
Atmospheric sulfate remains a major contributor to fine aerosol mass around the globe and is a known contributor to adverse effects on human health and ecosystems and can impact the Earth's radiative balance. Most sulfate is formed via a few dominant pathways (i.e., in-cloud reactions of S(IV) with H2O2 and O3 and gas phase oxidation of SO2 by OH); however the major oxidation pathways in existing models are unable to accurately represent high sulfate levels observed in some regions/seasons. Here we use CMAQv5.3 with an extended cloud chemistry module along with sulfur tracking capabilities to investigate the importance of different particulate sulfur formation pathways for an annual simulation over the N. Hemisphere.
Description:
In many locations around the globe, sulfate remains a major contributor to ambient PM2.5. Most sulfate formed in the atmosphere is attributable to a few dominant pathways (i.e., aqueous reactions of S(IV) with H2O2 and O3 and gas phase oxidation of SO2 by OH); however the major oxidation pathways in existing models are unable to accurately represent high sulfate levels observed in some regions/seasons (e.g., wintertime Beijing, Fairbanks). Recently, it was suggested that the high sulfate observations in wintertime Beijing might actually be a combination of sulfate and hydroxymethanesulfonate (HMS), a S(IV) species that can be formed in atmospheric droplets via reaction of SO2 and HCHO (Moch et al., 2018). Here we extend the sulfur tracking method capabilities in CMAQv5.3 to track the contributions of the additional sulfate production pathways available in CMAQ's AQCHEM-KMT cloud chemistry module, as well as update CMAQ to track HMS (the formation/decomposition of which is currently included in the AQCHEM-KMT mechanism) as a transported species. We apply the model for a 2016 hemispheric simulation and investigate the relative contributions of different pathways for sulfate production as well as identify any locations/seasons where HMS might be a significant contributor to particulate sulfur.