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| Titel |
Free radical modelling studies during the UK TORCH Campaign in Summer 2003 |
| VerfasserIn |
K. M. Emmerson, N. Carslaw, D. C. Carslaw, J. D. Lee, G. McFiggans, W. J. Bloss, T. Gravestock, D. E. Heard, J. Hopkins, T. Ingham, M. J. Pilling, S. C. Smith, M. Jacob, P. S. Monks |
| 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 ; 7, no. 1 ; Nr. 7, no. 1 (2007-01-12), S.167-181 |
| Datensatznummer |
250004352
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| Publikation (Nr.) |
 copernicus.org/acp-7-167-2007.pdf |
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| Zusammenfassung |
| The Tropospheric ORganic CHemistry experiment (TORCH) took place during the
heatwave of summer 2003 at Writtle College, a site 2 miles west of
Chelmsford in Essex and 25 miles north east of London. The experiment was
one of the most highly instrumented to date. A combination of a large number
of days of simultaneous, collocated measurements, a consequent wealth of
model constraints and a highly detailed chemical mechanism, allowed the
atmospheric chemistry of this site to be studied in detail. Between 25 July
and 31 August, the concentrations of the hydroxyl radical and the
hydroperoxy radical were measured using laser-induced fluorescence at low
pressure and the sum of peroxy radicals was measured using the peroxy
radical chemical amplifier technique. The concentrations of the radical
species were predicted using a zero-dimensional box model based on the
Master Chemical Mechanism version 3.1, which was constrained with the
observed concentrations of relatively long-lived species. The model included
a detailed parameterisation to account for heterogeneous loss of hydroperoxy
radicals onto aerosol particles. Quantile-quantile plots were used to assess
the model performance in respect of the measured radical concentrations. On
average, measured hydroxyl radical concentrations were over-predicted by
24%. Modelled and measured hydroperoxy radical concentrations agreed very
well, with the model over-predicting on average by only 7%. The sum of
peroxy radicals was under-predicted when compared with the respective
measurements by 22%. Initiation via OH was dominated by the reactions of
excited oxygen atoms with water, nitrous acid photolysis and the ozone
reaction with alkene species. Photolysis of aldehyde species was the main
route for initiation via HO2 and RO2. Termination, under all
conditions, primarily involved reactions with NOx for OH and
heterogeneous chemistry on aerosol surfaces for HO2. The OH chain
length varied between 2 and 8 cycles, the longer chain lengths occurring
before and after the most polluted part of the campaign. Peak local ozone
production of 17 ppb hr−1 occurred on 3 and 5 August,
signifying the importance of local chemical processes to ozone production on
these days. On the whole, agreement between model and measured radicals is
good, giving confidence that our understanding of atmospheres influenced by
nearby urban sources is adequate. |
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