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Chin, M., D. A. Chu, R. Levy, L. Remer, Y. Kaufman, B. N. Holben, T. Eck,
and P. Ginoux, 2004:
Aerosol composition and distributions in the northern
hemisphere during ACE-Asia: Results from global model, satellite
observations, and surface sunphotometer measurements.
J. Geophys. Res.,
109, D23S90, doi:10.1029/2004JD004829, 2004..
We analyze the aerosol distribution and composition in the Northern Hemisphere
during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) field
experiment in spring 2001. We use the Goddard Chemistry Aerosol Radiation and
Transport (GOCART) model in this study, in conjunction with satellite retrieval from the
Moderate-Resolution Imaging Spectroradiometer (MODIS) on EOS-Terra satellite and
Sun photometer measurements from the worldwide Aerosol Robotic Network
(AERONET). Statistical analysis methods including histograms, mean bias, root-meansquare
error, correlation coefficients, and skill scores are applied to quantify the
differences between the MODIS 1 1 gridded data, the daytime average AERONET
data, and the daily mean 2 2.5 resolution model results. Both MODIS and the model
show relatively high aerosol optical thickness (t) near the source regions of Asia, Europe,
and northern Africa, and they agree on major features of the long-range transport of
aerosols from their source regions to the neighboring oceans. The t values from MODIS
and from the model have similar probability distributions in the extratropical oceans and in
Europe, but MODIS is approximately 2–3 times as high as the model in North/Central
America and nearly twice as high in Asia and over the tropical/subtropical oceans.
Comparisons with the AERONET measurements in the Northern Hemisphere demonstrate
that in general the model and the AERONET data have comparable values and similar
probability distributions of t, whereas MODIS tends to report higher values of t over
land, particularly North/Central America. The MODIS high bias is primarily attributed
to the difficulties in land algorithm dealing with surface reflectance over inhomogeneous
and bright land surfaces, including mountaintops, arid areas, and areas of snow/ice melting
and with land/water mixed pixels. The model estimates that on average, sulfate, carbon,
dust, and sea salt comprise 30%, 25%, 32%, and 13%, respectively, of the 550-nm t
in April 2001 in the Northern Hemisphere, with 46% of the total t from anthropogenic
activities and 66% from fine mode aerosols.
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