The Tagged Species Source Apportionment (TSSA) algorithm is applied to study contributions to pollutants PM sulfate, SO2 and elemental carbon (EC) in Hong Kong by emitting sectors as well as non-emitting sources within and beyond the Pearl River Delta (PRD) region. We look at three areas of Hong Kong: western new towns, central downtown, and eastern countryside. Pollutant transport from beyond the PRD influenced all three areas during January and October 2004 but the source sectors impacting the three areas were different. Specifically, power plant SO2 from Hong Kong and Shenzhen, and vehicle EC from Shenzhen contribute to 11 ~ 66 % of SO2 concentration, and 33 ~ 75 % of EC concentration in the western new towns, respectively. Ships in and around Hong Kong contribute 8 ~ 56 % to the sulfate concentration in the downtown area, while local moving vehicles take up 28 ~ 81 % of the EC concentration there. The study also shows that diurnal variation of planetary boundary layer (PBL) causes day-night difference in SO2 by as much as 50 %. In addition, 13 ~ 38 % of all SO2 emissions have been converted to PM sulfate.