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Ozone and organic nitrates over the eastern United States: Sensitivity to isoprene chemistry

Mao, Jingqiu and Paulot, Fabien and Jacob, Daniel J. and Cohen, Ronald C. and Crounse, John D. and Wennberg, Paul O. and Keller, Christoph A. and Hudman, Rynda C. and Barkley, Michael P. and Horowitz, Larry W. (2013) Ozone and organic nitrates over the eastern United States: Sensitivity to isoprene chemistry. Journal of Geophysical Research. Atmospheres, 118 (19). pp. 11256-11268. ISSN 2169-897X.

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We implement a new isoprene oxidation mechanism in a global 3-D chemical transport model (GEOS-Chem). Model results are evaluated with observations for ozone, isoprene oxidation products, and related species from the International Consortium for Atmospheric Research on Transport and Transformation aircraft campaign over the eastern United States in summer 2004. The model achieves an unbiased simulation of ozone in the boundary layer and the free troposphere, reflecting canceling effects from recent model updates for isoprene chemistry, bromine chemistry, and HO2 loss to aerosols. Simulation of the ozone-CO correlation is improved relative to previous versions of the model, and this is attributed to a lower and reversible yield of isoprene nitrates, increasing the ozone production efficiency per unit of nitrogen oxides (NO_x ≡ NO + NO_2). The model successfully reproduces the observed concentrations of organic nitrates (∑ANs) and their correlations with HCHO and ozone. ∑ANs in the model is principally composed of secondary isoprene nitrates, including a major contribution from nighttime isoprene oxidation. The correlations of ∑ANs with HCHO and ozone then provide sensitive tests of isoprene chemistry and argue in particular against a fast isomerization channel for isoprene peroxy radicals. ∑ANs can provide an important reservoir for exporting NO_x from the U.S. boundary layer. We find that the dependence of surface ozone on isoprene emission is positive throughout the U.S., even if NO_x emissions are reduced by a factor of 4. Previous models showed negative dependences that we attribute to erroneous titration of OH by isoprene.

Item Type:Article
Related URLs:
URLURL TypeDescription
Paulot, Fabien0000-0001-7534-4922
Jacob, Daniel J.0000-0002-6373-3100
Cohen, Ronald C.0000-0001-6617-7691
Crounse, John D.0000-0001-5443-729X
Wennberg, Paul O.0000-0002-6126-3854
Additional Information:© 2013 American Geophysical Union. Received 17 May 2013; revised 30 July 2013; accepted 6 September 2013; published 1 October 2013. We thank the ICARTT science team for using their measurements. We thank Songmiao Fan and Vaishali Naik at GFDL for careful review. We also thank Ellie Browne (MIT), Havala Pye (EPA), Wendy Goliff (UC Riverside), Eloise Marais (Harvard), Katherine Travis (Harvard), Emily Fischer (Harvard), Mathew Evans (U of York), and Arlene Fiore (Columbia University) for helpful discussions. We also thank Christopher Holmes (UC Irvine) and Jenny Fisher (U of Wollongong) for help with IDL. J.M. and L.W.H. acknowledge the NOAA Climate Program Office’s grant NA13OAR4310071. F.P was supported by Harvard University Center for the Environment Fellowship. Work at Harvard was supported by the NASA Atmospheric Chemistry Modeling and Analysis Program.
Funding AgencyGrant Number
National Oceanic and Atmospheric Administration (NOAA)NA13OAR4310071
Harvard UniversityUNSPECIFIED
Subject Keywords:ozone; organic nitrates; isoprene chemistry; photooxidation; nitrogen export; nighttime chemistry
Issue or Number:19
Record Number:CaltechAUTHORS:20140317-111859201
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Official Citation:Mao, J., F. Paulot, D. J. Jacob, R. C. Cohen, J. D. Crounse, P. O. Wennberg, C. A. Keller, R. C. Hudman, M. P. Barkley, and L. W. Horowitz (2013), Ozone and organic nitrates over the eastern United States: Sensitivity to isoprene chemistry, J. Geophys. Res. Atmos., 118, 11,256–11,268, doi:10.1002/jgrd.50817.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:44353
Deposited By: Jason Perez
Deposited On:18 Mar 2014 20:10
Last Modified:18 Nov 2020 20:04

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