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| Titel |
Accumulation of aerosols over the Indo-Gangetic plains and southern slopes of the Himalayas: distribution, properties and radiative effects during the 2009 pre-monsoon season |
| VerfasserIn |
R. Gautam, N. C. Hsu, S. C. Tsay, K. M. Lau, B. Holben, S. Bell, A. Smirnov, C. Li, R. Hansell, Q. Ji, S. Payra, D. Aryal, R. Kayastha, K.-M. Kim |
| 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 ; 11, no. 24 ; Nr. 11, no. 24 (2011-12-20), S.12841-12863 |
| Datensatznummer |
250010282
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| Publikation (Nr.) |
 copernicus.org/acp-11-12841-2011.pdf |
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| Zusammenfassung |
| We examine the distribution of aerosols and associated optical/radiative
properties in the Gangetic-Himalayan region from simultaneous radiometric
measurements over the Indo-Gangetic Plains (IGP) and the foothill/southern
slopes of the Himalayas during the 2009 pre-monsoon season. Enhanced dust
transport extending from the Southwest Asian arid regions into the IGP,
results in seasonal mean (April–June) aerosol optical depths of over 0.6 –
highest over Southern Asia. The influence of dust loading is greater over
the Western IGP as suggested by pronounced coarse mode peak in aerosol size
distribution and spectral single scattering albedo (SSA). Transported dust
in the IGP, driven by prevailing westerly airmass, is found to be more
absorbing (SSA550 nm<0.9) than the near-desert region in Northwestern
(NW) India suggesting mixing with carbonaceous aerosols in the IGP. On the
contrary, significantly reduced dust transport is observed over eastern IGP
and foothill/elevated Himalayan slopes in Nepal where strongly absorbing
haze is prevalent, as indicated by lower SSA (0.85–0.9 at 440–1020 nm),
suggesting presence of more absorbing aerosols compared to IGP.
Additionally, our observations show a distinct diurnal pattern of aerosols
with characteristic large afternoon peak, from foothill to elevated mountain
locations, associated with increased upslope transport of pollutants – that
likely represent large-scale lifting of absorbing aerosols along the
elevated slopes during pre-monsoon season. In terms of radiative impact of
aerosols, over the source region of NW India, diurnal mean reduction in
solar radiation fluxes was estimated to be 19–23 Wm−2 at surface
(12–15% of the surface solar insolation). Furthermore, based on limited
observations of aerosol optical properties during the pre-monsoon period and
comparison of our radiative forcing estimates with published literature,
there exists a general spatial heterogeneity in the regional aerosol
forcing, associated with the absorbing aerosol distribution over northern
India, with both diurnal mean surface forcing and forcing efficiency over
the IGP exceeding that over Northwestern India. Finally, the role of the seasonal
progressive buildup of aerosol loading and water vapor is investigated in
the observed net aerosol radiative effect over Northwestern India. The radiative
impact of water vapor is found to amplify the net regional aerosol radiative
forcing suggesting that the two exert forcing in tandem leading to enhanced
surface cooling. It is suggested that water vapor contribution should be
taken into account while assessing aerosol forcing impact for this region
and other seasonally similar environments. |
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