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Formaldehyde Production from Isoprene Oxidation Across NOx RegimesThe chemical link between isoprene and formaldehyde (HCHO) is a strong, non-linear function of NOx (= 27 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 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 NOx values (roughly 0.1 - 2 ppbv), the prompt yield increases by a factor of 3 (from 0.3 to 0.9), while background HCHO increases by more than a factor of 2 (from 1.5 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 chemical box model. Both models reproduce the NOx 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. Moreover, we find that the total organic peroxy radical production rate is essentially independent of NOx, as the increase in oxidizing capacity with NOx is largely balanced by a decrease in VOC reactivity. Thus, the observed NOx dependence of HCHO mainly reflects the changing fate of organic peroxy radicals.
Document ID
20150021531
Acquisition Source
Goddard Space Flight Center
Document Type
Preprint (Draft being sent to journal)
Authors
Wolfe, G. M.
(Maryland Univ. Baltimore County Baltimore, MD, United States)
Kaiser, J.
(Wisconsin Univ. Madison, WI, United States)
Hanisco, T. F.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Keutsch, F. N.
(Harvard Univ. Cambridge, MA, United States)
de Gouw, J. A.
(Colorado Univ. Boulder, CO, United States)
Gilman, J. B.
(Colorado Univ. Boulder, CO, United States)
Graus, M.
(Colorado Univ. Boulder, CO, United States)
Hatch, C. D.
(Hendrix Coll. Conway, AR, United States)
Holloway, J.
(Colorado Univ. Boulder, CO, United States)
Horowitz, L. W.
(Princeton Univ. NJ, United States)
Lee, B. H.
(Washington Univ. Seattle, WA, United States)
Lerner, B. M.
(Colorado Univ. Boulder, CO, United States)
Lopez-Hilifiker, F.
(Washington Univ. Seattle, WA, United States)
Mao, J.
(Princeton Univ. NJ, United States)
Marvin, M.
(Maryland Univ. College Park, MD, United States)
Peischl, J.
(Colorado Univ. Boulder, CO, United States)
Pollack, I. B.
(Colorado Univ. Boulder, CO, United States)
Roberts, J. M.
(National Oceanic and Atmospheric Administration Boulder, CO, United States)
Ryerson, T. B.
(National Oceanic and Atmospheric Administration Boulder, CO, United States)
Thornton, J. A.
(Washington Univ. Seattle, WA, United States)
Veres, P. R.
(Colorado Univ. Boulder, CO, United States)
Warneke, C.
(Colorado Univ. Boulder, CO, United States)
Date Acquired
November 20, 2015
Publication Date
October 29, 2015
Publication Information
Publisher: Atmospheric Chemistry and Physics
Subject Category
Earth Resources And Remote Sensing
Inorganic, Organic And Physical Chemistry
Report/Patent Number
GSFC-E-DAA-TN27799
Funding Number(s)
CONTRACT_GRANT: NNX14AK97H
CONTRACT_GRANT: EPA-STAR-83540601
CONTRACT_GRANT: NNH10ZDA001N-SEAC4RS
CONTRACT_GRANT: NNX14AP48G
CONTRACT_GRANT: NNX15AT34A
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
VOC
atmospheric chemistry
isoprene
formaldehyde
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