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| Titel |
OH regeneration from methacrolein oxidation investigated in the atmosphere simulation chamber SAPHIR |
| VerfasserIn |
H. Fuchs, I.-H. Acir, B. Bohn, T. Brauers, H.-P. Dorn, R. Häseler, A. Hofzumahaus, F. Holland, M. Kaminski, X. Li, K. Lu, A. Lutz, S. Nehr, F. Rohrer, R. Tillmann, R. Wegener, A. Wahner |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 15 ; Nr. 14, no. 15 (2014-08-08), S.7895-7908 |
| Datensatznummer |
250118931
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| Publikation (Nr.) |
 copernicus.org/acp-14-7895-2014.pdf |
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| Zusammenfassung |
| Hydroxyl radicals (OH) are the most important reagent for the
oxidation of trace gases in the atmosphere. OH concentrations measured during
recent field campaigns in isoprene-rich environments were unexpectedly large.
A number of studies showed that unimolecular reactions of organic peroxy
radicals (RO2) formed in the initial reaction step of isoprene with OH
play an important role for the OH budget in the atmosphere at low mixing
ratios of nitrogen monoxide (NO) of less than 100 pptv. It has also been
suggested that similar reactions potentially play an important role for
RO2 from other compounds. Here, we investigate the oxidation of
methacrolein (MACR), one major oxidation product of isoprene, by OH in
experiments in the simulation chamber SAPHIR under controlled atmospheric
conditions. The experiments show that measured OH concentrations are
approximately 50% larger than calculated by the Master Chemical Mechanism
(MCM) for conditions of the experiments (NO mixing ratio of 90 pptv). The
analysis of the OH budget reveals an OH source that is not accounted for in
MCM, which is correlated with the production rate of RO2 radicals from
MACR. In order to balance the measured OH destruction rate, 0.77 OH radicals
(1σ error: ± 0.31) need to be additionally reformed from each
reaction of OH with MACR. The strong correlation of the missing OH source
with the production of RO2 radicals is consistent with the concept of OH
formation from unimolecular isomerization and decomposition reactions of
RO2. The comparison of observations with model calculations gives a lower
limit of 0.03 s−1 for the reaction rate constant if the OH source is
attributed to an isomerization reaction of MACR-1-OH-2-OO and MACR-2-OH-2-OO
formed in the MACR + OH reaction as suggested in the literature
(Crounse et al., 2012). This fast isomerization reaction would be a competitor to
the reaction of this RO2 species with a minimum of 150 pptv NO. The
isomerization reaction would be the dominant reaction pathway for this
specific RO2 radical in forested regions, where NO mixing ratios are
typically much smaller. |
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