Roadside suspended particulates at heavily trafficked urban sites of Hong Kong – Seasonal variation and dependence on meteorological conditions

In this study, the seasonal variation of different types of particulates was investigated in a fixed roadside station in heavily trafficked urban area of Hong Kong. Aerosol samples for total suspended particles (TSP), PM10 and PM2.5 were collected from June 1998 to May 1999 at a roadside site. Meteorological conditions such as relative humidity (RH), rainfall and prevailing wind direction were found to affect the mass concentration of TSP, PM10 and coarse particulates at roadside level. Large size particles had an apparent seasonal variation, with higher concentration level in winter and lower in summer. The dry continental winter monsoon and the wet oceanic summer monsoon are the dominating factors. On the other hand, annual variation of PM2.5 is relatively insignificant, suggesting that they are mainly from local traffic emission. PM10 accounted for 62% of the TSP, while PM2.5 accounted for 46%. The annual PM2.5/PM10 is high with PM2.5 responsible for 74% of PM10. In our heavily trafficked roadside fixed site, TSP exceeded the annual average of the Hong Kong Air Quality Objective by a factor of 1.53 while PM10 exceeded by 1.39. The annual average concentration of PM2.5 exceeded the National Ambient Air Quality Standard (NAAQS) annual average of 15 μg m−3 by a factor of 3.8 and is a cause of concern. A total of the 24 h average PM2.5 exceeded NAAQS by 33%. According to our data reported, fine particulate pollution is serious in Hong Kong.