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Epoxide as a Precursor to Secondary Organic Aerosol Formation from Isoprene Photooxidation in the Presence of Nitrogen Oxides
Citation:
Lin, Y., H. Zhang, H. Pye, Z. Zhang, W. Marth, S. Park, M. Arashiro, T. Cui, S. Budisulistiorini, K. Sexton, W. Vizuete, Y. Xie, D. Luecken, I. Piletic, E. Edney, L. Bartolotti, A. Gold, AND J. Surratt. Epoxide as a Precursor to Secondary Organic Aerosol Formation from Isoprene Photooxidation in the Presence of Nitrogen Oxides. PNAS (PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES). National Academy of Sciences, WASHINGTON, DC, 110(17):6718-6723, (2013).
Impact/Purpose:
The National Exposure Research Laboratory′s (NERL′s) Atmospheric Modeling and Analysis 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:
Isoprene is a substantial contributor to the global secondary organic aerosol (SOA) burden, with implications for public health and the climate system. The mechanism by which isoprene-derived SOA is formed and the influence of environmental conditions, however, remain unclear. We present evidence from controlled smog chamber experiments and field measurements that in the presence of high levels of nitrogen oxides (NOx = NO + NO2), typical of urban atmospheres, 2-methyloxirane-2-carboxylic acid (methacrylic acid epoxide; MAE) is a precursor to known isoprene-derived SOA tracers, and ultimately to SOA. We propose that MAE arises from decomposition of the OH adduct of methacryloylperoxynitrate (HOMPAN). This hypothesis is supported by the similarity of SOA constituents derived from MAE to those from photooxidation of isoprene, methacrolein, and MPAN under high-NOx conditions. Strong support is further derived from computational chemistry calculations and Community Multiscale Air Quality (CMAQ) model simulations, yielding predictins consistent with field overvations. Field measurements taken in Chapel Hill, NC, considered along with the modeling results indicate the atmospheric significance and relevance of MAE chemistry across the U.S., especially in urban areas heavily impacted by isoprene emissions. Identification of MAE implies a major role of atmospheric epoxides in forming SOA from isoprene photooxidation. Updating current atmospheric modeling frameworks with MAE chemistry could improve the way that SOA has been attributed to isoprene based on ambient tracer measurements, and lead to SOA parameterizations that better capture the dependency of yield on NOx.
URLs/Downloads:
LINETAL_REVISION_MAIN_WFIGS FINAL FINAL.PDF (PDF, NA pp, 984.112 KB, about PDF)LINETALSUPPORTINGFIGSTABLES FINAL.PDF (PDF, NA pp, 2224.572 KB, about PDF)
Proceedings of the National Academy of Sciences (PNAS)
