 |
| Titel |
Atmospheric Brown Clouds in the Himalayas: first two years of continuous observations at the Nepal Climate Observatory-Pyramid (5079 m) |
| VerfasserIn |
P. Bonasoni, P. Laj, A. Marinoni, M. Sprenger, F. Angelini, J. Arduini, U. Bonafè, F. Calzolari, T. Colombo, S. Decesari, C. Biagio, A. G. Sarra, F. Evangelisti, R. Duchi, M. C. Facchini, S. Fuzzi, G. P. Gobbi, M. Maione, A. Panday, F. Roccato, K. Sellegri, H. Venzac, G. P. Verza, P. Villani, E. Vuillermoz, P. Cristofanelli |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 10, no. 15 ; Nr. 10, no. 15 (2010-08-13), S.7515-7531 |
| Datensatznummer |
250008702
|
| Publikation (Nr.) |
 copernicus.org/acp-10-7515-2010.pdf |
|
|
|
|
|
| Zusammenfassung |
This paper provides a detailed description of the atmospheric conditions
characterizing the high Himalayas, thanks to continuous observations begun
in March 2006 at the Nepal Climate Observatory-Pyramid (NCO-P) located at
5079 m a.s.l. on the southern foothills of Mt. Everest, in the framework of
ABC-UNEP and SHARE-Ev-K2-CNR projects. The work presents a characterization
of meteorological conditions and air-mass circulation at NCO-P during the
first two years of activity. The mean values of atmospheric pressure,
temperature and wind speed recorded at the site were: 551 hPa, −3.0 °C,
4.7 m s−1, respectively. The highest seasonal values of temperature
(1.7 °C) and relative humidity (94%) were registered during the
monsoon season, which was also characterized by thick clouds, present in
about 80% of the afternoon hours, and by a frequency of cloud-free sky of
less than 10%. The lowest temperature and relative humidity seasonal
values were registered during winter, −6.3 °C and 22%, respectively,
the season being characterised by mainly cloud-free sky conditions and rare
thick clouds. The summer monsoon influenced rain precipitation (seasonal
mean: 237 mm), while wind was dominated by flows from the bottom of the
valley (S–SW) and upper mountain (N–NE).
The atmospheric composition at NCO-P has been studied thanks to measurements
of black carbon (BC), aerosol scattering coefficient, PM1, coarse particles
and ozone. The annual behaviour of the measured parameters shows the highest
seasonal values during the pre-monsoon (BC: 316.9 ng m−3, PM1: 3.9 μg m−3, scattering coefficient: 11.9 Mm−1, coarse
particles: 0.37 cm−3 and O3: 60.9 ppbv), while the lowest concentrations
occurred during the monsoon (BC: 49.6 ng m−3, PM1: 0.6 μg m−3, scattering coefficient: 2.2 Mm−1, and O3: 38.9 ppbv)
and, for coarse particles, during the post-monsoon (0.07 cm−3. At
NCO-P, the synoptic-scale circulation regimes present three principal
contributions: Westerly, South-Westerly and Regional, as shown by the
analysis of in-situ meteorological parameters and 5-day LAGRANTO back-trajectories.
The influence of the brown cloud (AOD>0.4) extending over Indo–Gangetic
Plains up to the Himalayan foothills has been evaluated by analysing the
in-situ concentrations of the ABC constituents. This analysis revealed that brown
cloud hot spots mainly influence the South Himalayas during the pre-monsoon,
in the presence of very high levels of atmospheric compounds (BC: 1974.1 ng m−3, PM1: 23.5 μg m−3,
scattering coefficient: 57.7 Mm−1, coarse particles: 0.64 cm−3, O3: 69.2 ppbv,
respectively). During this season 20% of the days were characterised by a
strong brown cloud influence during the afternoon, leading to a 5-fold
increased in the BC and PM1 values, in comparison with seasonal means. Our
investigations provide clear evidence that, especially during the
pre-monsoon, the southern side of the high Himalayan valleys represent a
"direct channel" able to transport brown cloud pollutants up to 5000 m a.s.l., where the pristine atmospheric composition can be strongly
influenced. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|