This title appears in the Scientific Report : 2014 

OH regeneration from methacrolein oxidation investigated in the atmosphere simulation chamber SAPHIR
Fuchs, H. (Corresponding author)
Acir, I.-H. / Bohn, B. / Brauers, T. / Dorn, H.-P. / Häseler, R. / Hofzumahaus, A. / Holland, F. / Kaminski, M. / Li, Xin / Lu, K. / Lutz, A. / Nehr, Sascha / Rohrer, F. / Tillmann, R. / Wegener, R. / Wahner, A.
Troposphäre; IEK-8
Atmospheric chemistry and physics / Discussions, 14 (2014) 4, S. 5197 - 5231
Katlenburg-Lindau EGU 2014
10.5194/acpd-14-5197-2014
Journal Article
Helmholtz Interdisciplinary Doctoral Training in Energy and Climate Research (HITEC)
Tropospheric trace substances and their transformation processes
Trace gas and aerosol processes in the troposphere
OpenAccess
Please use the identifier: http://hdl.handle.net/2128/5942 in citations.
Please use the identifier: http://dx.doi.org/10.5194/acpd-14-5197-2014 in citations.
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 current chemical models for conditions of the experiments (NO mixing ratio of 90 pptv). The analysis of the OH budget reveals a so far unaccounted OH source, which is correlated with the production rate of RO2 radicals from MACR. In order to balance the measured OH destruction rate, (0.77±0.3) OH radicals need to be additionally reformed from each OH that has reacted 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 one RO2 species formed in the MACR+OH reaction as suggested in literature. This fast isomerization reaction would be competitive to the reaction of this RO2 species with minimum 150 pptv NO