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Investigation of the alpha-pinene photooxidation by OH in the atmospheric simulation chamber SAPHIR

Journal article
Authors M. Rolletter
M. Kaminski
I. H. Acir
B. Bohn
H. P. Dorn
X. Li
Anna Lutz
S. Nehr
F. Rohrer
R. Tillmann
R. Wegener
A. Hofzumahaus
A. Kiendler-Scharr
A. Wahner
H. Fuchs
Published in Atmospheric Chemistry and Physics
Volume 19
Issue 18
Pages 11635-11649
ISSN 1680-7316
Publication year 2019
Published at Department of Chemistry and Molecular Biology
Pages 11635-11649
Language en
Links dx.doi.org/10.5194/acp-19-11635-201...
Keywords laser-induced fluorescence, volatile organic-compounds, gas-phase, reactions, absorption cross-sections, beta-pinene, 2-methyl-3-butene-2-ol mbo, tropospheric degradation, photolysis, frequencies, initiated oxidation, radicals, Environmental Sciences & Ecology, Meteorology & Atmospheric Sciences
Subject categories Meteorology and Atmospheric Sciences, Geochemistry

Abstract

The photooxidation of the most abundant monoterpene, alpha-pinene, by the hydroxyl radical (OH) was investigated at atmospheric concentrations in the atmospheric simulation chamber SAPHIR. Concentrations of nitric oxide (NO) were below 120 pptv. Yields of organic oxidation products are determined from measured time series giving values of 0.11 +/- 0.05, 0.19 +/- 0.06, and 0.05 +/- 0.03 for formaldehyde, acetone, and pinonaldehyde, respectively. The pinonaldehyde yield is at the low side of yields measured in previous laboratory studies, ranging from 0.06 to 0.87. These studies were mostly performed at reactant concentrations much higher than observed in the atmosphere. Time series of measured radical and trace-gas concentrations are compared to results from model calculations applying the Master Chemical Mechanism (MCM) 3.3.1. The model predicts pinonaldehyde mixing ratios that are at least a factor of 4 higher than measured values. At the same time, modeled hydroxyl and hydroperoxy (HO2) radical concentrations are approximately 25 % lower than measured values. Vereecken et al. (2007) suggested a shift of the initial organic peroxy radical (RO2) distribution towards RO2 species that do not yield pinonaldehyde but produce other organic products. Implementing these modifications reduces the model-measurement gap of pinonaldehyde by 20 % and also improves the agreement in modeled and measured radical concentrations by 10 %. However, the chemical oxidation mechanism needs further adjustment to explain observed radical and pinonaldehyde concentrations. This could be achieved by adjusting the initial RO2 distribution, but could also be done by implementing alternative reaction channels of RO2 species that currently lead to the formation of pinonaldehyde in the model.

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