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| Titel |
Quantifying the Fate of Stablised Criegee Intermediates under Atmospheric Conditions |
| VerfasserIn |
Mike Newland, Andrew Rickard, Mohammed Alam, Luc Vereecken, Amalia Muñoz, Milagros Ródenas, William Bloss |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250086232
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| Publikation (Nr.) |
 EGU/EGU2014-59.pdf |
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| Zusammenfassung |
| The products of alkene ozonolysis have been shown in field experiments to convert SO2 to
H2SO4. One fate of H2SO4 formed in the atmosphere is the formation of sulphate aerosol.
This has been reported to contribute - 0.4 W m-2 to anthropogenic radiative forcing via the
direct aerosol effect and can also contribute to the indirect aerosol effect, currently one of the
greatest uncertainties in climate modelling.
The observed SO2 oxidation has been proposed to arise from reactions of the carbonyl oxide,
or Criegee Intermediate (CI), formed during alkene ozonolysis reactions, with SO2. Direct
laboratory experiments have confirmed that stabilised CIs (SCIs) react more quickly with
SO2 (k > 10-11 cm3 s-1) than was previously thought.
The major sink for SCI in the troposphere is reaction with water vapour. The importance of
the SO2 + SCI reaction in H2SO4 formation has been shown in modelling work to be
critically dependent on the ratio of the rate constants for the reaction of the SCI
with SO2 and with H2O. Such modelling work has suggested that the SCI + SO2
reaction is only likely to be important in regions with high alkene emissions, e.g.
forests.
Here we present results from a series of ozonolysis experiments performed at the EUPHORE
atmospheric simulation chamber, Valencia. These experiments measure the loss of SO2, in
the presence of an alkene (ethene, cis-but-2-ene and 2,3-dimethyl butene), as a function of
water vapour. From these experiments we quantify the relative rates of reaction of the three
smallest SCI with water and SO2 and their decomposition rates. In addition the results appear
to suggest that the conversion of SO2 to H2SO4 during alkene ozonolysis may be
inconsistent with the SCI + SO2 mechanism alone, particularly at high relative
humidities.
The results suggest that SCI are likely to provide at least an equivalent sink for SO2 to that of
OH in the troposphere, in agreement with field observations. This work highlights the
importance of alkene ozonolysis not only as a non-photolytic source of HOx but additionally
as a source of other important atmospheric oxidants and moves towards quantifying some of
the important sinks of SCI in the atmosphere. |
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