Light scattering and absorption coefficients were measured from September 1997 to April 1999 at a station at Cape D'Aguilar, a remote area at the southeastern tip of Hong Kong. The sum of the coefficients was converted to particulate mass concentration of aerosols and compared with those measured at other urban stations. Using back trajectories, the air masses arriving Hong Kong can be classified into seven types. Air masses originating in the Asian continent generally brought in higher aerosol concentrations than those from the ocean. The South Marine Circulation type trajectories (SMC) brought in the lowest aerosol mass concentration of about 10 mug m(-3) measured at the Cape D'Aguilar station. This can be used as the value for background mass concentration in the Hong Kong region. Based on measurements at stations located at different parts in the territory the sources of aerosols in Hong Kong were speculated to be mainly due to emissions from the Asian continent and local sources in winter. Local emissions were thought to be mainly responsible for the aerosol concentrations in summer.