The following diagrams show the path of air mass reaching Hong Kong for the next three days (15 - 17 March 2011). The paths show that the air mass reaching Hong Kong mainly comes from the Luzon Strait on 15 March, and from mainland China as well as the vicinity of Hong Kong on 16 and 17 March.
  

Figure 1. Trajectory of air mass reaching Hong Kong at 8 a.m. 15 March 2011

Figure 2. Trajectory of air mass reaching Hong Kong at 8 a.m. 16 March 2011

Figure 3. Trajectory of air mass reaching Hong Kong at 8 a.m. 17 March 2011