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Regional Impacts of extending inorganic and organic cloud chemistry with AQCHEM-KMT
Citation:
Fahey, K., N. Sareen, Bill Hutzell, AND D. Luecken. Regional Impacts of extending inorganic and organic cloud chemistry with AQCHEM-KMT. 16th Annual CMAS Conference, Chapel Hill, North Carolina, October 23 - 25, 2017.
Impact/Purpose:
This is a poster describing the impacts of an expanded cloud chemistry mechanism on modeled pollutant concentrations. Additional in-cloud SOA chemistry can lead to significant increases in predicted cloud SOA levels in the summer, both at the surface and aloft. Additional inorganic chemistry can impact sulfate and nitrate concentrations in the winter. This work is expected to contribute to more accurate modeling of the spatiotemporal evolution of pollutants in CMAQ and the NGAQM.
Description:
Starting with CMAQ version 5.1, AQCHEM-KMT has been offered as a readily expandable option for cloud chemistry via application of the Kinetic PreProcessor (KPP). AQCHEM-KMT treats kinetic mass transfer between the gas and aqueous phases, ionization, chemical kinetics, droplet scavenging of interstitial aerosol, and wet deposition occurring within clouds. Here we investigate the impacts of expanding the AQCHEM-KMT mechanism with additional inorganic and organic chemistry with regional CMAQ applications for summer and winter periods. The cloud chemistry added here includes the formation of organic acids from glyoxal, methylglyoxal, glycolaldehyde, and acetic acid (replacing the in-cloud SOA parameterization of CMAQ’s standard AQCHEM), sulfate formation from NO2 and HNO4, as well as several additional reactions of radicals and other inorganic and organic species. Preliminary summer simulations indicate an increase in in-cloud SOA concentrations as well as a changing spatial distribution, in part due to the addition of new precursors to in-cloud SOA, which may originate from other sources than those precursors in the base model. Initial winter simulations show greater (and variable) impacts on inorganic species, with sulfate concentrations increasing and nitrate decreasing in much of the eastern United States. Because the addition of new species and reactions to the cloud chemical mechanism will lead to an even greater model computational burden, we also revisit using equilibrium assumptions to dictate the distribution of species between phases and ions. An attempt is made to identify those species/conditions for which such simplifying assumptions can be made to improve model efficiency, while minimizing adverse impacts on accuracy.
