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| Titel |
Contribution of atmospheric processes affecting the dynamics of air pollution in South-Western Europe during a typical summertime photochemical episode |
| VerfasserIn |
M. Gonçalves, P. Jiménez-Guerrero, J. M. Baldasano |
| 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 ; 9, no. 3 ; Nr. 9, no. 3 (2009-02-03), S.849-864 |
| Datensatznummer |
250006815
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| Publikation (Nr.) |
 copernicus.org/acp-9-849-2009.pdf |
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| Zusammenfassung |
| The southern Mediterranean region frequently experiences critical levels of
photochemical pollutants during summertime. In order to account for the
contribution of different atmospheric processes during this type of
episodes, the WRF-ARW/HERMES/CMAQ modelling system was applied with high
resolution (1 km2, 33 sigma vertical layers, 1 h) to assess the
different dynamics in a coastal environment and an inland-continental zone:
the North-Eastern and Central Iberian Peninsula (NEIP and CIP,
respectively). The former is characterized by a very complex terrain, while
the latter behaves as a flat area, which clearly affects the pattern of
local flows. A representative type of photochemical pollution episode
(occurring over 78% of summer days) which occurred during 17–18 June,
2004 is selected as the study period. The CMAQ Integrated Process Rate
provides the hourly contributions of atmospheric processes to net O3,
NOx and NMVOCs concentrations. The O3 photochemical formation
occurs mainly in downwind areas from the main NOx emission sources
during midday. At surface level it accounts for 50 to 75 μg m−3 h−1.
The urban areas and main roads, as main sources of NOx
emissions, act as O3 sinks, quenching up to −200 μg m−3 per
hour during the traffic circulation peaks. The O3 concentration
gradient generated, larger during daytime, increases the contribution of
diffusion processes to ground-level O3 (up to 200 μg m−3 h−1
fluxes, mainly from upper vertical layers). The maximum positive
contributions of gas-phase chemistry to O3 occur in the coastal domain
at high levels (around 500 to 1500 m a.g.l.), while in the continental domain
they take place in the whole atmospheric column under the PBL. The transport
of ozone precursors by advective flows determines the location of the
maximum O3 surface concentrations. The O3 chemical formation
involves the oxidation of less NMVOCs in the NEIP than in the CIP domains,
due to differences in chemical sensitivity between these areas. The dry
deposition is an important sink in the lowest layer of the model, together
with vertical diffusion flows. Finally, the contributions from cloud
processes, wet deposition and heterogeneous chemistry are negligible during
the whole episode, characterized by a high solar radiation and neither
precipitation nor cloudiness. This process analysis provides new
quantitative information about the origin of the peaks of O3 and its
precursors, aiding the design of abatement strategies in South-Western
Europe. |
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