The following diagrams show the path of air mass reaching Hong Kong for the next three days (16 - 18 March 2011). The paths show that the air mass reaching Hong Kong during the period mainly comes from mainland China and the vicinity of Hong Kong.
  

Figure 1. Trajectory of air mass reaching Hong Kong at 8 a.m. 16 March 2011

Figure 2. Trajectory of air mass reaching Hong Kong at 8 a.m. 17 March 2011

Figure 3. Trajectory of air mass reaching Hong Kong at 8 a.m. 18 March 2011