Formaldehyde production from isoprene oxidation across NOx regimes

G M Wolfe; J Kaiser; T F Hanisco; F N Keutsch; J A de Gouw; J B Gilman; M Graus; C D Hatch; J Holloway; L W Horowitz; B H Lee; B M Lerner; F Lopez-Hilifiker; J Mao; M R Marvin; J Peischl; I B Pollack; J M Roberts; T B Ryerson; J A Thornton; P R Veres; C Warneke

doi:10.5194/acp-16-2597-2016

Formaldehyde production from isoprene oxidation across NO_x regimes

Atmos Chem Phys. 2016;16(4):2597-2610. doi: 10.5194/acp-16-2597-2016. Epub 2016 Mar 2.

Authors

G M Wolfe^{1

2}, J Kaiser³, T F Hanisco², F N Keutsch⁴, J A de Gouw^{5

6}, J B Gilman^{5

6}, M Graus^{5

6}, C D Hatch⁷, J Holloway^{5

6}, L W Horowitz⁸, B H Lee⁹, B M Lerner^{5

6}, F Lopez-Hilifiker⁹, J Mao^{8

10}, M R Marvin¹¹, J Peischl^{5

6}, I B Pollack^{5

6}, J M Roberts⁶, T B Ryerson⁶, J A Thornton⁹, P R Veres^{5

6}, C Warneke^{5

6}

Affiliations

¹ Joint Center for Earth Systems Technology, University of Maryland Baltimore County, Baltimore, MD, USA.
² Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA.
³ Department of Chemistry, University of Wisconsin-Madison, Madison, WI, USA.
⁴ School of Engineering and Applied Sciences and Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA.
⁵ Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO, USA.
⁶ Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO, USA.
⁷ Department of Chemistry, Hendrix College, Conway, AR, USA.
⁸ NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA.
⁹ Department of Atmospheric Sciences, University of Washington, Seattle, WA, USA.
¹⁰ Program in Atmospheric and Oceanic Sciences, Princeton University, Princeton, NJ.
¹¹ Department of Chemistry, University of Maryland, College Park, MD, USA.

Abstract

The chemical link between isoprene and formaldehyde (HCHO) is a strong, non-linear function of NO_x (= NO + NO₂). This relationship is a linchpin for top-down isoprene emission inventory verification from orbital HCHO column observations. It is also a benchmark for overall photochemical mechanism performance with regard to VOC oxidation. Using a comprehensive suite of airborne in situ observations over the Southeast U.S., we quantify HCHO production across the urban-rural spectrum. Analysis of isoprene and its major first-generation oxidation products allows us to define both a "prompt" yield of HCHO (molecules of HCHO produced per molecule of freshly-emitted isoprene) and the background HCHO mixing ratio (from oxidation of longer-lived hydrocarbons). Over the range of observed NO_x values (roughly 0.1 - 2 ppbv), the prompt yield increases by a factor of 3 (from 0.3 to 0.9 ppbv ppbv^-1), while background HCHO increases by a factor of 2 (from 1.6 to 3.3 ppbv). We apply the same method to evaluate the performance of both a global chemical transport model (AM3) and a measurement-constrained 0-D steady state box model. Both models reproduce the NO_x dependence of the prompt HCHO yield, illustrating that models with updated isoprene oxidation mechanisms can adequately capture the link between HCHO and recent isoprene emissions. On the other hand, both models under-estimate background HCHO mixing ratios, suggesting missing HCHO precursors, inadequate representation of later-generation isoprene degradation and/or under-estimated hydroxyl radical concentrations. Detailed process rates from the box model simulation demonstrate a 3-fold increase in HCHO production across the range of observed NO_x values, driven by a 100% increase in OH and a 40% increase in branching of organic peroxy radical reactions to produce HCHO.

Abstract

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