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| Titel |
A multi-model evaluation of aerosols over South Asia: common problems and possible causes |
| VerfasserIn |
X. Pan, M. Chin, R. Gautam, H. Bian, D. Kim, P. R. Colarco, T. L. Diehl, T. Takemura, L. Pozzoli, K. Tsigaridis, S. Bauer, N. Bellouin |
| 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 ; 15, no. 10 ; Nr. 15, no. 10 (2015-05-28), S.5903-5928 |
| Datensatznummer |
250119763
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| Publikation (Nr.) |
 copernicus.org/acp-15-5903-2015.pdf |
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| Zusammenfassung |
| Atmospheric pollution over South Asia attracts special attention due to its
effects on regional climate, water cycle and human health. These effects are
potentially growing owing to rising trends of anthropogenic aerosol
emissions. In this study, the spatio-temporal aerosol distributions over
South Asia from seven global aerosol models are evaluated against aerosol
retrievals from NASA satellite sensors and ground-based measurements for the
period of 2000–2007. Overall, substantial underestimations of aerosol
loading over South Asia are found systematically in most model simulations.
Averaged over the entire South Asia, the annual mean aerosol optical depth
(AOD) is underestimated by a range 15 to 44% across models compared
to MISR (Multi-angle Imaging SpectroRadiometer), which is the lowest bound among various satellite AOD retrievals
(from MISR, SeaWiFS (Sea-Viewing Wide Field-of-View Sensor), MODIS (Moderate Resolution Imaging Spectroradiometer) Aqua and Terra). In particular during the
post-monsoon and wintertime periods (i.e., October–January), when
agricultural waste burning and anthropogenic emissions dominate, models fail
to capture AOD and aerosol absorption optical depth (AAOD) over the
Indo–Gangetic Plain (IGP) compared to ground-based Aerosol Robotic Network (AERONET) sunphotometer
measurements. The underestimations of aerosol loading in models generally
occur in the lower troposphere (below 2 km) based on the comparisons of
aerosol extinction profiles calculated by the models with those from Cloud–Aerosol Lidar with Orthogonal Polarization
(CALIOP)
data. Furthermore, surface concentrations of all aerosol components
(sulfate, nitrate, organic aerosol (OA) and black carbon (BC)) from the models are
found much lower than in situ measurements in winter. Several possible
causes for these common problems of underestimating aerosols in models
during the post-monsoon and wintertime periods are identified: the aerosol
hygroscopic growth and formation of secondary inorganic aerosol are
suppressed in the models because relative humidity (RH) is biased far too low in
the boundary layer and thus foggy conditions are poorly represented in current models, the nitrate aerosol is either missing or inadequately
accounted for, and emissions from agricultural waste burning and biofuel
usage are too low in the emission inventories. These common problems and
possible causes found in multiple models point out directions for future
model improvements in this important region. |
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