Extreme Particulate Levels at a Western Pacific Coastal City: The Influence of Meteorological Factors and the Contribution of Long-Range Transport

Abstract

The 4-year data sets (1998–2001) of PM10 and other gaseous pollutants at four rural and urban monitoring sites provided by Environmental Protection Department of Hong Kong have been analyzed for days of extremely high and low PM10 levels. The annual means of PM10 concentrations are between 37 and 57 μg/m3. The level of high PM10 concentration is defined from the comparison of local and international standards. Episode days are mainly controlled by different meteorological conditions: the continental outflow, the land-sea breeze/weak synoptic forcings and the approaching tropical cyclones. Integrated approaches have been used to distinguish between the predominantly “territory wide” and “long-range transport” (LRT) episode days. Case studies of these types of episodes are presented and the number of episode days per year for each type has been estimated. It is found that the LRT contributions are significant and account for ∼66% of the PM10 episode days. Very high correlations between CO and PM10 concentrations, and between SO2 and PM10 concentrations, can be found during the “territory wide” episode days which implies the important contributions of fossil fuel combustion to the PM10 episodes. The number of “low level” PM10 days per year has decreased by a factor near 3 from 1998 to 2001. Precipitation scavenging is the major process causing low levels of PM10, irrespective of the associated weather systems. The regional annual background level is ∼9 μg/m3. With the exception of seasalt components, the average elemental concentrations of major inorganic species are similar for all of the sites during LRT events and constitute representative compositions of PM10 during such events.