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| Titel |
Aerosol pollution potential from major population centers |
| VerfasserIn |
D. Kunkel, H. Tost, M. G. Lawrence |
| 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 ; 13, no. 8 ; Nr. 13, no. 8 (2013-04-19), S.4203-4222 |
| Datensatznummer |
250018602
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| Publikation (Nr.) |
 copernicus.org/acp-13-4203-2013.pdf |
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| Zusammenfassung |
| Major population centers (MPCs), or megacities, represent the largest of
growing urban agglomerations with major societal and environmental
implications. In terms of air quality, they are seen as localized but strong
emission sources of aerosols and trace gases which in turn affect air
pollution levels in the city or in downwind regions. In the state-of-the-art
atmospheric chemistry general circulation model EMAC, generic aerosol
and gas-phase tracers with equal emission source strengths at 46 MPC locations are
used to study the balance between local pollution build-up and pollution
export, either vertically into the upper troposphere or horizontally in the
lower troposphere. The insoluble gas-phase tracers with fixed lifetimes are
transported with the atmospheric circulation, while the aerosol tracers also
undergo gravitational sedimentation as well as dry and wet deposition
processes. The strength of low-level tracer export depends on the location of
the emission source and prevailing meteorology, in particular on atmospheric
stability and the height of the boundary layer and the mixing out of this
layer. In contrast, vertical transport of tracer mass depends on the tracer's
solubility: the more soluble a tracer is, the less mass reaches altitudes
above five kilometers. Hence, the mass of insoluble gas-phase tracer above
five kilometers can be up to ten times higher than the hydrophilic aerosol
mass from the same source. In the case of aerosol tracers, pollution build-up
around the source is determined by meteorological factors which have only
indirect effects on tracer lifetime, like surface wind, boundary layer
height, and turbulent mixing, as well as those which affect the lifetime of
the tracers such as precipitation. The longer a tracer stays in the
atmosphere, the lower is the relative importance of the location of the
source to the atmospheric mass, and thus the lower is the relative local
pollution build-up. We further use aerosol deposition fields to estimate
regions with high deposition, that is more than 1% or more than
5% of the corresponding tracer emission deposited in this region. In
doing so, we find that the high deposition areas are larger for aerosols with
diameters of 10.0 μm, and these differ less between the MPCs than
for aerosols with diameters smaller than 2.5 μm due to faster
deposition. Furthermore, cities in regions with high precipitation rates or
unfavorable geographic locations, e.g., in a basin, suffer most of this high
deposition. Most of the high deposition occurs over land, although about
50% of the MPCs are located along coastlines. By folding the aerosol
deposition fields with geographical distributions of cropland, pasture, and
forest, the impact on different land ecosystems is assessed. In general,
forest is exposed most to deposition from MPCs while pastureland is least
affected. Moreover, the impact on humans, measured with a threshold
exceedance of pollutant surface mixing ratios, is more dependent on
population densities than on the size of the area with a certain mixing
ratio. |
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