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Air pollutant transport in a coastal environment. Part 1: Two-dimensional simulations of sea-breeze and mountain effectsOver the southern California coastal region, observations of the vertical distributions of pollutants show that maximum concentrations can occur within temperature inversion layers well above the surface. A mesoscale model is used to study the dynamical phenomena that cause such layers, including sea breezes and mountain flows, and to study the characteristics of air pollutant transport in a coastal environment capped by a temperature inversion. The mathematical and physical structure of the model is described. Two-dimensional simulations corresponding to four configurations of coastal plains and mountains are discussed. The simulations reveal that pollutant transport over a coastal plain is strongly influenced by the topographic configuration, including the height of coastal mountains and their distance from the coastline. Sea breezes induced by land-sea thermal contrasts, as well as upslope winds induced along mountain flanks, both create vertical transport that can lead to the formation of elevated pollution layers. The sea-breeze circulation generates pollution layers by undercutting the mixed layer and lofting pollutants into the stable layer. Heating of mountain slopes acts to vent pollutants above the mountain ridge during the day; during the evening, pollutants can be injected directly into the inversion layer from the decaying upslope flows. In a land-sea configuration with mountains close to the coastline, the sea breeze and heated-mountain flow are strongly coupled. In the afternoon, this interaction can produce upslope flow from which polluted air is detrained into the inversion layer as a return circulation. When the mountains lie farther inland, however, pollutants may be trapped aloft when the mixed layer stabilizes in the late afternoon. As the nocturnal boundary layer forms over the coast in the evening, polluted mixed-layer air is effectively left behind in the inversion layer. In the Los Angeles Basin, the formation mechanism for elevated polluted layers is most similar to our cases with inland mountains.
Document ID
19950034016
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Lu, Rong
(Univ. of California, Los Angeles, CA United States)
Turco, Richard P.
(Univ. of California, Los Angeles, CA United States)
Date Acquired
August 16, 2013
Publication Date
August 1, 1994
Publication Information
Publication: Journal of the Atmospheric Sciences
Volume: 51
Issue: 15
ISSN: 0022-4928
Subject Category
Meteorology And Climatology
Accession Number
95A65615
Funding Number(s)
CONTRACT_GRANT: NSF ATM-89-11836
Distribution Limits
Public
Copyright
Other

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