This title appears in the Scientific Report :
2017
Please use the identifier:
http://hdl.handle.net/2128/16645 in citations.
Please use the identifier: http://dx.doi.org/10.5194/acp-2017-1095 in citations.
The atmospheric impacts of monoterpene ozonolysis on global stabilised Criegee intermediate budgets and SO2 oxidation: experiment, theory and modelling
The atmospheric impacts of monoterpene ozonolysis on global stabilised Criegee intermediate budgets and SO2 oxidation: experiment, theory and modelling
The gas-phase reaction of alkenes with ozone is known to produce stabilised Criegee intermediates (SCIs). These biradical/zwitterionic species have the potential to act as atmospheric oxidants for trace pollutants such as SO2, enhancing the formation of sulfate aerosol with impacts on air quality an...
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Personal Name(s): | Newland, Mike J. (Corresponding author) |
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Rickard, Andrew R. (Corresponding author) / Sherwen, Tomás / Evans, Mathew J. / Vereecken, Luc / Muñoz, Amalia / Ródenas, Milagros / Bloss, William J. | |
Contributing Institute: |
Troposphäre; IEK-8 |
Published in: | Atmospheric chemistry and physics / Discussions, 1095 (2017) S. 1 - 65 |
Imprint: |
Katlenburg-Lindau
EGU
2017
|
DOI: |
10.5194/acp-2017-1095 |
Document Type: |
Journal Article |
Research Program: |
Tropospheric trace substances and their transformation processes |
Link: |
OpenAccess |
Publikationsportal JuSER |
Please use the identifier: http://dx.doi.org/10.5194/acp-2017-1095 in citations.
The gas-phase reaction of alkenes with ozone is known to produce stabilised Criegee intermediates (SCIs). These biradical/zwitterionic species have the potential to act as atmospheric oxidants for trace pollutants such as SO2, enhancing the formation of sulfate aerosol with impacts on air quality and health, radiative transfer and climate. However, the importance of this chemistry is uncertain as a consequence of limited understanding of the abundance and atmospheric fate of SCIs. In this work we apply experimental, theoretical and numerical modelling methods to quantify the atmospheric impacts, abundance, and fate, of the structurally diverse SCIs derived from the ozonolysis of monoterpenes, the second most abundant group of unsaturated hydrocarbons in the atmosphere. We have investigated the removal of SO2 by SCI formed from the ozonolysis of three monoterpenes (-pinene, -pinene and limonene) in the presence of varying amounts of water vapour in large-scale simulation chamber experiments. The SO2 removal displays a clear dependence on water vapour concentration, but this dependence is not linear across the range of [H2O] explored. At low [H2O] a strong dependence of SO2 removal on [H2O] is observed, while at higher [H2O] this dependence becomes much weaker. This is interpreted as being caused by the production of a variety of structurally (and hence chemically) different SCI in each of the systems studied, each displaying different rates of reaction with water and of unimolecular rearrangement/decomposition. The determined rate constants, k(SCI+H2O), for those SCI that react primarily with H2O range from 4–310 × 10−15 cm3 s−1. For those SCI that predominantly react unimolecularly, determined rates range from 130–240 s−1. These values are in line with previous results for the (analogous) stereo-specific SCI system of syn/anti-CH3CHOO. The experimental results are interpreted through theoretical studies of the SCI unimolecular reactions and bimolecular reactions with H2O, characterised for -pinene and -pinene at the M06-2X/aug-cc-pVTZ level of theory. The theoretically derived rates agree with the experimental results within the uncertainties. A global modelling study, applying the experimental results within the GEOS-Chem chemical transport model, suggests that > 98 % of the total monoterpene derived global SCI burden is comprised of SCI whose structure determines that they react slowly with water, and whose atmospheric fate is dominated by unimolecular reactions. Seasonally averaged boundary layer concentrations of monoterpene-derived SCI reach up to 1.2 × 104 cm−3 in regions of elevated monoterpene emissions in the tropics. Reactions of monoterpene derived SCI with SO2 account for < 1 % globally but may account for up to 50 % of the gas-phase SO2 removal over areas of tropical forests, with significant localised impacts on the formation of sulfate aerosol, and hence the lifetime and distribution of SO2. |