Sourcedependent properties

Figure 10 shows the results from 72 h backward trajectories and displayed the air parcel sources at the altitude of 1 km (Fig. 10(a)) and the sources of all dust cloud layers (nine cases) in Fig. 10(b). These trajectories were generated by HYSPLIT model of NOAA (National Oceanic and Atmospheric Administration). The trajectories of Fig. 10(a) are under cloud-free and dust-free conditions over our site. The times of trajectories are in accordance with the times of BGA cases in 2002-2004. The heights

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 DR (>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 et al.12

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