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Fig. 10. The results of (a) air parcel sources at altitude 1 km and (b) dust clouds sources
from 72 h backward trajectories from the HYSPLIT model.
where
0.1) are used for tracing dust-cloud sources. For BGA cases,
the air parcels mainly come from the coastal industrial areas of China. The
dust-clouds were traced back from the nearby desert regions of Northern
China through populated and industrialized areas. Therefore, there were
ample opportunities that the dust particles had interaction with moisture
and pollutants to form clouds. Those clouds have complex composition and
interaction with aerosol, dust, and moisture. The related discussion can be
found in the study of Nee
DR
(
>
et al. 12
4. Summary
In this chapter, the differences in the optical properties of aerosol and
cloud are studied based on the depolarization ratio (
δ a ) measurements. The
polarization lidar observations can provide quantitative information about
phase composition of clouds. From the statistics of analysis, the following
conclusions can be made:
(1) Most aerosols are distributed below 2 km over our location and their
depolarization ratios are smaller than 0.06. The effect of relative
humidity on depolarization ratio is expected as the aerosols are more
nonspherical in the dry air. The backscattering ratio increases steeply
when relative humidity is higher than 60%-70%.
(2) Clouds with higher extinction coecient and depolarization ratio are
caused by dust particles that are mainly transported from Northern
China. This is supported by HYSPLIT model. The interactions of
aerosols and clouds may be caused by pollutants and humidity.
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