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Formaldehyde production from isoprene oxidation across NOx regimes
- Source :
- Atmospheric Chemistry and Physics. 16:2597-2610
- Publication Year :
- 2016
- Publisher :
- Copernicus GmbH, 2016.
-
Abstract
- The chemical link between isoprene and formaldehyde (HCHO) is a strong, nonlinear function of NOx (i.e., 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 US, 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 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 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 underestimate background HCHO mixing ratios, suggesting missing HCHO precursors, inadequate representation of later-generation isoprene degradation and/or underestimated hydroxyl radical concentrations. Detailed process rates from the box model simulation demonstrate a 3-fold increase in HCHO production across the range of observed NOx values, driven by a 100 % increase in OH and a 40 % increase in branching of organic peroxy radical reactions to produce HCHO.
- Subjects :
- Atmospheric Science
Ozone
010504 meteorology & atmospheric sciences
Chemical transport model
Formaldehyde
010501 environmental sciences
Photochemistry
01 natural sciences
chemistry.chemical_compound
chemistry
Atmospheric chemistry
Mixing ratio
Hydroxyl radical
NOx
Isoprene
0105 earth and related environmental sciences
Subjects
Details
- ISSN :
- 16807324
- Volume :
- 16
- Database :
- OpenAIRE
- Journal :
- Atmospheric Chemistry and Physics
- Accession number :
- edsair.doi...........9f9ae235568377491be2a15cd626ba85