Understanding the impact of recent advances in isoprene photooxidation on simulations of regional air quality
Abstract
The CMAQ (Community Multiscale Air Quality) us model in combination with observations for INTEX-NA/ICARTT (Intercontinental Chemical Transport Experiment–North America/International Consortium for Atmospheric Research on Transport and Transformation) 2004 are used to evaluate recent advances in isoprene oxidation chemistry and provide constraints on isoprene nitrate yields, isoprene nitrate lifetimes, and NO_x recycling rates. We incorporate recent advances in isoprene oxidation chemistry into the SAPRC-07 chemical mechanism within the US EPA (United States Environmental Protection Agency) CMAQ model. The results show improved model performance for a range of species compared against aircraft observations from the INTEX-NA/ICARTT 2004 field campaign. We further investigate the key processes in isoprene nitrate chemistry and evaluate the impact of uncertainties in the isoprene nitrate yield, NO_x (NO_x = NO + NO_2) recycling efficiency, dry deposition velocity, and RO_2 + HO_2 reaction rates. We focus our examination on the southeastern United States, which is impacted by both abundant isoprene emissions and high levels of anthropogenic pollutants. We find that NO_x concentrations increase by 4–9% as a result of reduced removal by isoprene nitrate chemistry. O3 increases by 2 ppbv as a result of changes in NO_x. OH concentrations increase by 30%, which can be primarily attributed to greater HO_x production. We find that the model can capture observed total alkyl and multifunctional nitrates (∑ANs) and their relationship with O_3 by assuming either an isoprene nitrate yield of 6% and daytime lifetime of 6 hours or a yield of 12% and lifetime of 4 h. Uncertainties in the isoprene nitrates can impact ozone production by 10% and OH concentrations by 6%. The uncertainties in NO_x recycling efficiency appear to have larger effects than uncertainties in isoprene nitrate yield and dry deposition velocity. Further progress depends on improved understanding of isoprene oxidation pathways, the rate of NOx recycling from isoprene nitrates, and the fate of the secondary, tertiary, and further oxidation products of isoprene.
Additional Information
© Author(s) 2013. This work is distributed under the Creative Commons Attribution 3.0 License. Published by Copernicus Publications on behalf of the European Geosciences Union. Received: 5 September 2012; Published in Atmos. Chem. Phys. Discuss.: 17 October 2012; Revised: 26 January 2013; Accepted: 12 July 2013; Published: 27 August 2013. We thank the entire INTEX-NA/ICARTT team for the use of their measurement data. We also thank Barron Henderson, Melinda Beaver, Tad Kleindienst, and John Crounse for helpful conversations. This research was supported by the National Research Council Research Associateship Program pursued at the US Environmental Protection Agency. Fabien Paulot acknowledges support from a NASA Earth and Space Science fellowship. Disclaimer: although this article has been reviewed by the EPA and approved for publication, it does not necessarily reflect EPA policies or views. Edited by: J. ThorntonAttached Files
Published - acp-13-8439-2013.pdf
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- Eprint ID
- 41522
- Resolver ID
- CaltechAUTHORS:20130925-111149297
- National Research Council Research Associateship Program
- NASA Earth and Space Science Fellowship
- Created
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2013-09-25Created from EPrint's datestamp field
- Updated
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2021-11-10Created from EPrint's last_modified field
- Caltech groups
- Division of Geological and Planetary Sciences