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Examining the role of NOx and acidity on organic aerosol formation through predictions of key isoprene aerosol species in the United States
Citation:
Pye, H., R. Pinder, I. Piletic, Y. Xie, S. Capps, Y. Lin, J. Surratt, Z. Zhang, A. Gold, D. Luecken, Bill Hutzell, M. Jaoui, J. Offenberg, Tad E. Kleindienst, M. Lewandowski, AND Edward O. Edney. Examining the role of NOx and acidity on organic aerosol formation through predictions of key isoprene aerosol species in the United States. Presented at Gordon Conference on Atmospheric Chemistry, West Dover, VT, July 28 - August 02, 2013.
Impact/Purpose:
The National Exposure Research Laboratory (NERL) Atmospheric Modeling and Analysis Division (AMAD) conducts research in support of EPA mission to protect human health and the environment. AMAD research program is engaged in developing and evaluating predictive atmospheric models on all spatial and temporal scales for forecasting the 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:
Isoprene is a significant contributor to organic aerosol in the Southeastern United States. Later generation isoprene products, specifically isoprene epoxydiols (IEPOX) and methacryloylperoxynitrate (MPAN), have been identified as SOA precursors. The contribution of each pathway to aerosol depends on the amount of NOx available and is thus subject to anthropogenic influences. In this work we update the parameterization of SOA from isoprene in the Community Multiscale Air Quality (CMAQ) model to predict SOA from IEPOX and a new MPAN oxidation product identified by Lin et al. (accepted in PNAS). These new parameterizations are a function of acidity as well as the availability of water, sulfate, and nitrate. CMAQ is able to predict concentrations of key isoprene-derived aerosol species such as methylglyceric acid, methyl tetrols, IEPOX-derived organosulfates, MPAN-derived organosulfates, and dimers. These species are compared to ambient observations to provide insight into the role of acidity and NOx on SOA formation and may serve as indicators of an anthropogenic control on biogenic SOA