Evaluating the Isoprene Oxidation Mechanism Using Aircraft Observations from SENEX 2013

The chemical mechanism for isoprene oxidation is associated with a great deal of uncertainty. As a result, implementation of the isoprene oxidation mechanism by regional models may lead to misrepresentation of ozone, organic aerosol, and related species important to air quality. Formaldehyde (HCHO) is a major product of isoprene oxidation and thus provides observational constraint on the mechanism. The SouthEast NEXus (SENEX) 2013 aircraft campaign provides observations of HCHO over the Southeast United States, an environment that is high in isoprene but variable in NOx, with the lowest concentrations of NOx in remote regions such as the Ozarks and the highest near cities and power plants. Such a range of conditions provides a unique opportunity to map out the sensitivity of HCHO to changes in the isoprene oxidation mechanism. We use the University of Washington Chemical Model (UWCMv2.2) to evaluate the HCHO dependence on isoprene and NOx throughout the range of conditions observed during SENEX. Particular emphasis will be placed on the effects of newly proposed mechanisms, including enhanced OH regeneration and updated alkyl nitrate chemistry.