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| Titel |
Influence of isoprene chemical mechanism on modelled changes in tropospheric ozone due to climate and land use over the 21st century |
| VerfasserIn |
O. J. Squire, A. T. Archibald, P. T. Griffiths, M. E. Jenkin, D. Smith, J. A. Pyle |
| 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. 9 ; Nr. 15, no. 9 (2015-05-07), S.5123-5143 |
| Datensatznummer |
250119699
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| Publikation (Nr.) |
 copernicus.org/acp-15-5123-2015.pdf |
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| Zusammenfassung |
| Isoprene is a~precursor to tropospheric ozone, a key pollutant and greenhouse
gas. Anthropogenic activity over the coming century is likely to cause large
changes in atmospheric CO2 levels, climate and land use, all of which will
alter the global vegetation distribution leading to changes in isoprene
emissions. Previous studies have used global chemistry–climate models to
assess how possible changes in climate and land use could affect isoprene
emissions and hence tropospheric ozone. The chemistry of isoprene oxidation,
which can alter the concentration of ozone, is highly complex, therefore it
must be parameterised in these models. In this work, we compare the effect of
four different reduced isoprene chemical mechanisms, all currently used in
Earth system models, on tropospheric ozone. Using a box model we compare
ozone in these reduced schemes to that in a more explicit scheme (the Master Chemical Mechanism)
over a range of NOx and isoprene emissions, through the use of O3
isopleths. We find that there is some variability, especially at high
isoprene emissions, caused by differences in isoprene-derived NOx
reservoir species. A global model is then used to examine how the different
reduced schemes respond to potential future changes in climate, isoprene
emissions, anthropogenic emissions and land use change. We find that,
particularly in isoprene-rich regions, the response of the schemes varies
considerably. The wide-ranging response is due to differences in the model
descriptions of the peroxy radical chemistry, particularly their relative
rates of reaction towards NO, leading to ozone formation, or HO2, leading
to termination. Also important is the yield of isoprene nitrates and
peroxyacyl nitrate precursors from isoprene oxidation. Those schemes that
produce less of these NOx reservoir species, tend to produce more ozone
locally and less away from the source region. We also note changes in other
key oxidants such as NO3 and OH (due to the inclusion of additional
isoprene-derived HOx recycling pathways). These have implications for secondary organic aerosol
formation, as does the inclusion of an epoxide formation pathway in one of
the mechanisms. By combining the emissions and O3 data from all of the
global model integrations, we are able to construct isopleth plots comparable
to those from the box model analysis. We find that the global and box model
isopleths show good qualitative agreement, suggesting that comparing chemical
mechanisms with a box model in this framework is a useful tool for assessing
mechanistic performance in complex global models. We conclude that as the
choice of reduced isoprene mechanism may alter both the magnitude and sign of
the ozone response, how isoprene chemistry is parameterised in perturbation
experiments such as these is a crucially important consideration. More
measurements and laboratory studies are needed to validate these reduced
mechanisms especially under high-volatile-organic-compound, low-NOx conditions. |
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