Study of atmospheric aerosols and wet deposition in Hong Kong

Abstract

Atmospheric chemistry, specifically related to aerosols and wet deposition in Hong Kong and the influencing factors including the source contributions and meteorological controls in Asia is studied in this thesis. It begins with the environmental setting of Hong Kong and the current understandings of the above two topics, then specific aims of the PhD research have been set to achieve new contributions to the knowledge of atmospheric chemistry, using the methodology mentioned in Chapter 2. The following summarizes the key findings of the study: (1) Under the influence of the summer monsoon, the sea salt concentrations depend on the synoptic wind speed; (2) Under the impacts of the Asian dust storm, PM10 concentrations of Hong Kong can approach/exceed the air quality standards. The storms transport from the source to Hong Kong in 2-5 days; (3) PM10 episode days are mainly controlled by the continental outflow, land-sea breeze/weak synoptic forcings and approaching tropical cyclones. The long-range transport contributions account for ~66% of the episode days; (4) The crustal and anthropogenic species concentrations in PM10 are elevated under the influence of the winter monsoon and the approaching tropical cyclone. However nss-SO42- and NO3- concentrations from continental outflows are decreasing, starting from 1998; (5) The rainwater in Hong Kong is acidic. This finding is not caused by strong emission strengths of acidic gas precursors, compared to other Asian cities, but due to the lack of acid-neutralizing sources; (6) The rainwater in a Taiwan site is less acidic than that in a Hong Kong site. The most abundant species in the Taiwan site are sea- salts but nss-SO42- and H+ in the Hong Kong site. Chloride depletion is minimal in both sites; and (7) The curve (concentration against raindrop radius) patterns for all the species are similar but depend on the starting time of sampling within a rain event. Below-cloud sulphur dioxide scavenging contributes at most 60% of the sulphate concentration in a single raindrop.