You are here:
Investigating expanded chemistry in CMAQ clouds
Citation:
Fahey, K., H. Pye, D. Luecken, AND K. Baker. Investigating expanded chemistry in CMAQ clouds. 14th Annual CMAS Conference, Chapel Hill, NC, October 05 - 07, 2015.
Impact/Purpose:
The National Exposure Research Laboratory’s Atmospheric Modeling Division (AMAD) conducts research in support of EPA’s mission to protect human health and the environment. AMAD’s research program is engaged in developing and evaluating predictive atmospheric models on all spatial and temporal scales for forecasting the Nation’s air quality and for assessing changes in air quality and air pollutant exposures, as affected by changes in ecosystem management and regulatory decisions. AMAD is responsible for providing a sound scientific and technical basis for regulatory policies based on air quality models to improve ambient air quality. The models developed by AMAD are being used by EPA, NOAA, and the air pollution community in understanding and forecasting not only the magnitude of the air pollution problem, but also in developing emission control policies and regulations for air quality improvements.
Description:
Clouds and fogs significantly impact the amount, composition, and spatial distribution of gas and particulate atmospheric species, not least of which through the chemistry that occurs in cloud droplets.ﾠ Atmospheric sulfate is an important component of fine aerosol mass and in an environment where clouds or fogs are present, aqueous phase production of SO4 can dominate over gas phase production (Seigneur and Saxena, 1988).ﾠ More recent studies have suggested that the aqueous phase of clouds and wet aerosols may be an important medium for the production of secondary organic aerosol (Ervens et al., 2014; Ervens et al., 2011; McNeill, 2015).Due in large part to computational constraints, historically, only a simple description of aqueous phase chemistry has been implemented in many chemical transport models. Aqueous phase chemistry in CMAQ, for example, is based on a simple sulfur oxidation scheme from RADM (Walcek and Taylor, 1986) with few updates to the mechanism in recent years (Carlton et al., 2008).ﾠ Cloud and fog chemistry and redistribution between gas/aerosol/aqueous phases may have important impacts for a myriad of species, and as computational capabilities have expanded, so should the investigation and treatment of more complete aqueous chemistry mechanisms in regional modeling frameworks.ﾠHere we employ the Kinetic PreProcessor (KPP) to investigate the impacts of expanding CMAQ?s baseline aqueous chemical mechanism.ﾠ KPP has been used previously to generate Fortran90 code to simultaneously treat kinetic mass transfer between the gas-aqueous phases, ionic dissociation/association, wet deposition, scavenging of interstitial aerosol, and chemical kinetics (Fahey et al., 2013; Baek et al., 2011).ﾠ We expand the baseline mechanism to include the aqueous phase formation of SOA in cloud water from isoprene epoxydiols and MPAN, as well as examine the impacts of implementing more rigorous mechanisms for inorganic and organic aqueous phase chemistry (e.g., Pandis and Seinfeld, 1989; Fahey and Pandis, 2001).ﾠ We will examine the baseline and expanded model results for summer and winter periods and include comparisons between modeled and observational data.
