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| Titel |
Atmospheric isoprene ozonolysis: impacts of stabilised Criegee intermediate reactions with SO2, H2O and dimethyl sulfide |
| VerfasserIn |
M. J. Newland, A. R. Rickard, L. Vereecken, A. Muñoz, M. Ródenas, W. J. Bloss |
| 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 ; 15, no. 16 ; Nr. 15, no. 16 (2015-08-26), S.9521-9536 |
| Datensatznummer |
250119993
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| Publikation (Nr.) |
 copernicus.org/acp-15-9521-2015.pdf |
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| Zusammenfassung |
| Isoprene is the dominant global biogenic volatile organic compound (VOC)
emission. Reactions of isoprene with ozone are known to form stabilised
Criegee intermediates (SCIs), which have recently been shown to be
potentially important oxidants for SO2 and NO2 in the atmosphere;
however the significance of this chemistry for SO2 processing
(affecting sulfate aerosol) and NO2 processing (affecting NOx
levels) depends critically upon the fate of the SCIs with respect to reaction
with water and decomposition. Here, we have investigated the removal of
SO2 in the presence of isoprene and ozone, as a function of humidity,
under atmospheric boundary layer conditions. The SO2 removal displays a
clear dependence on relative humidity, confirming a significant reaction for
isoprene-derived SCIs with H2O. Under excess SO2 conditions, the
total isoprene ozonolysis SCI yield was calculated to be 0.56 (±0.03). The observed SO2 removal kinetics are consistent with a relative
rate constant, k(SCI + H2O) / k(SCI + SO2), of 3.1 (±0.5) × 10−5
for isoprene-derived SCIs. The relative rate constant
for k(SCI decomposition) / k(SCI+SO2) is 3.0
(±3.2) × 1011 cm−3. Uncertainties are ±2σ and represent
combined systematic and precision components. These kinetic parameters are
based on the simplification that a single SCI species is formed in isoprene
ozonolysis, an approximation which describes the results well across the
full range of experimental conditions. Our data indicate that
isoprene-derived SCIs are unlikely to make a substantial contribution to
gas-phase SO2 oxidation in the troposphere. We also present results
from an analogous set of experiments, which show a clear dependence of
SO2 removal in the isoprene–ozone system as a function of dimethyl
sulfide concentration. We propose that this behaviour arises from a rapid
reaction between isoprene-derived SCIs and dimethyl sulfide (DMS); the observed SO2 removal
kinetics are consistent with a relative rate constant, k(SCI + DMS) / k(SCI + SO2), of 3.5 (±1.8). This result suggests that SCIs may
contribute to the oxidation of DMS in the atmosphere and that this process
could therefore influence new particle formation in regions impacted by
emissions of unsaturated hydrocarbons and DMS. |
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