US EPA

1936515 

Journal Article 

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

Mao, J; Paulot, F; Jacob, DJ; Cohen, RC; Crounse, JD; Wennberg, PO; Keller, CA; Hudman, RC; Barkley, MP; Horowitz, LW 

2013 

Yes 

Journal of Geophysical Research: Atmospheres
ISSN: 2169-897X
EISSN: 2169-8996 

AMER GEOPHYSICAL UNION 

WASHINGTON 

118 

19 

11256–11268 

10.1002/jgrd.50817 

WOS:000330266700054 

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 ICARTT 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 (OPE) per unit of nitrogen oxides (NOx ≡ NO + NO2). 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 NOx from the US boundary layer. We find that the dependence of surface ozone on isoprene emission is positive throughout the US, even if NOx emissions are reduced by a factor of 4. Previous models showed negative dependences that we attribute to erroneous titration of OH by isoprene. 

ozone; organic nitrates; isoprene chemistry; photooxidation; nitrogen export; nighttime chemistry