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| Titel |
Simulating regional scale secondary organic aerosol formation during the TORCH 2003 campaign in the southern UK |
| VerfasserIn |
D. Johnson, S. R. Utembe, M. E. Jenkin, R. G. Derwent, G. D. Hayman, M. R. Alfarra, H. Coe, G. McFiggans |
| 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 ; 6, no. 2 ; Nr. 6, no. 2 (2006-02-08), S.403-418 |
| Datensatznummer |
250003415
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| Publikation (Nr.) |
 copernicus.org/acp-6-403-2006.pdf |
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| Zusammenfassung |
| A photochemical trajectory model has been used to simulate the chemical
evolution of air masses arriving at the TORCH field campaign site in the
southern UK during late July and August 2003, a period which included a
widespread and prolonged photochemical pollution episode. The model
incorporates speciated emissions of 124 non-methane anthropogenic VOC and
three representative biogenic VOC, coupled with a comprehensive description
of the chemistry of their degradation. A representation of the gas/aerosol
absorptive partitioning of ca. 2000 oxygenated organic species generated in
the Master Chemical Mechanism (MCM v3.1) has been implemented, allowing
simulation of the contribution to organic aerosol (OA) made by semi- and
non-volatile products of VOC oxidation; emissions of primary organic aerosol
(POA) and elemental carbon (EC) are also represented. Simulations of total
OA mass concentrations in nine case study events (optimised by comparison
with observed hourly-mean mass loadings derived from aerosol mass
spectrometry measurements) imply that the OA can be ascribed to three
general sources: (i) POA emissions; (ii) a "ubiquitous" background
concentration of 0.7 µg m-3; and (iii) gas-to-aerosol transfer of
lower volatility products of VOC oxidation generated by the regional scale
processing of emitted VOC, but with all partitioning coefficients increased
by a species-independent factor of 500. The requirement to scale the
partitioning coefficients, and the implied background concentration, are
both indicative of the occurrence of chemical processes within the aerosol
which allow the oxidised organic species to react by association and/or
accretion reactions which generate even lower volatility products, leading
to a persistent, non-volatile secondary organic aerosol (SOA). The
contribution of secondary organic material to the simulated OA results in
significant elevations in the simulated ratio of organic carbon (OC) to EC,
compared with the ratio of 1.1 assigned to the emitted components. For the
selected case study events, [OC]/[EC] is calculated to lie in the range 2.7-9.8,
values which are comparable with the high end of the range reported
in the literature. |
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