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| Titel |
Aerosol optical properties and radiative forcing in the high Himalaya based on measurements at the Nepal Climate Observatory-Pyramid site (5079 m a.s.l.) |
| VerfasserIn |
S. Marcq, P. Laj, J. C. Roger, P. Villani, K. Sellegri, P. Bonasoni, A. Marinoni, P. Cristofanelli, G. P. Verza, M. Bergin |
| 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 ; 10, no. 13 ; Nr. 10, no. 13 (2010-07-02), S.5859-5872 |
| Datensatznummer |
250008587
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| Publikation (Nr.) |
 copernicus.org/acp-10-5859-2010.pdf |
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| Zusammenfassung |
| Intense anthropogenic emissions over the Indian sub-continent lead to the
formation of layers of particulate pollution that can be transported to the
high altitude regions of the Himalaya-Hindu-Kush (HKH). Aerosol particles
contain a substantial fraction of strongly absorbing material, including
black carbon (BC), organic compounds (OC), and dust all of which can
contribute to atmospheric warming, in addition to greenhouse gases. Using a
3-year record of continuous measurements of aerosol optical properties, we
present a time series of key climate relevant aerosol properties including
the aerosol absorption (σap) and scattering (σsp)
coefficients as well as the single-scattering albedo (w0). Results of
this investigation show substantial seasonal variability of these
properties, with long range transport during the pre- and post-monsoon
seasons and efficient precipitation scavenging of aerosol particles during
the monsoon season. The monthly averaged scattering coefficients range from
0.1 Mm−1 (monsoon) to 20 Mm−1 while the average absorption
coefficients range from 0.5 Mm−1 to 3.5 Mm−1. Both have their
maximum values during the pre-monsoon period (April) and reach a minimum
during Monsoon (July–August). This leads to dry w0 values from 0.86
(pre-monsoon) to 0.79 (monsoon) seasons. Significant diurnal variability due
to valley wind circulation is also reported. Using aerosol optical depth
(AOD) measurements, we calculated the resulting direct local radiative
forcing due to aerosols for selected air mass cases. We found that the
presence of absorbing particulate material can locally induce an additional
top of the atmosphere (TOA) forcing of 10 to 20 W m−2 for the first
atmospheric layer (500 m above surface). The TOA positive forcing depends on
the presence of snow at the surface, and takes place preferentially during
episodes of regional pollution occurring on a very regular basis in the
Himalayan valleys. Warming of the first atmospheric layer is paralleled by a
substantial decrease of the amount of radiation reaching the surface. The
surface forcing is estimated to range from −4 to −20 W m−2 for
small-scale regional pollution events and large-scale pollution events,
respectively. The calculated surface forcing is also very dependent on
surface albedo, with maximum values occurring over a snow-covered surface.
Overall, this work presents the first estimates of aerosol direct radiative
forcing over the high Himalaya based on in-situ aerosol measurements, and
results suggest a TOA forcing significantly greater than the IPCC reported
values for green house gases. |
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