Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5753133 | Atmospheric Environment | 2017 | 12 Pages |
Abstract
Isoprene oxidation schemes vary greatly among gas-phase chemical mechanisms, with potentially significant ramifications for air quality modeling and interpretation of satellite observations in biogenic-rich regions. In this study, in situ observations from the 2013 SENEX mission are combined with a constrained 0-D photochemical box model to evaluate isoprene chemistry among five commonly used gas-phase chemical mechanisms: CB05, CB6r2, MCMv3.2, MCMv3.3.1, and a recent version of GEOS-Chem. Mechanisms are evaluated and inter-compared with respect to formaldehyde (HCHO), a high-yield product of isoprene oxidation. Though underestimated by all considered mechanisms, observed HCHO mixing ratios are best reproduced by MCMv3.3.1 (normalized mean bias = â15%), followed by GEOS-Chem (â17%), MCMv3.2 (â25%), CB6r2 (â32%) and CB05 (â33%). Inter-comparison of HCHO production rates reveals that major restructuring of the isoprene oxidation scheme in the Carbon Bond mechanism increases HCHO production by only â¼5% in CB6r2 relative to CB05, while further refinement of the complex isoprene scheme in the Master Chemical Mechanism increases HCHO production by â¼16% in MCMv3.3.1 relative to MCMv3.2. The GEOS-Chem mechanism provides a good approximation of the explicit isoprene chemistry in MCMv3.3.1 and generally reproduces the magnitude and source distribution of HCHO production rates. We analytically derive improvements to the isoprene scheme in CB6r2 and incorporate these changes into a new mechanism called CB6r2-UMD, which is designed to preserve computational efficiency. The CB6r2-UMD mechanism mimics production of HCHO in MCMv3.3.1 and demonstrates good agreement with observed mixing ratios from SENEX (â14%). Improved simulation of HCHO also impacts modeled ozone: at â¼0.3 ppb NO, the ozone production rate increases â¼3% between CB6r2 and CB6r2-UMD, and rises another â¼4% when HCHO is constrained to match observations.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Atmospheric Science
Authors
Margaret R. Marvin, Glenn M. Wolfe, Ross J. Salawitch, Timothy P. Canty, Sandra J. Roberts, Katherine R. Travis, Kenneth C. Aikin, Joost A. de Gouw, Martin Graus, Thomas F. Hanisco, John S. Holloway, Gerhard Hübler, Jennifer Kaiser, Frank N. Keutsch,