Abundance and Seasonal Characteristics of Elemental and Organic Carbon in Hong Kong PM sub(10)

We review here measurements of elemental carbon (EC) and organic carbon (OC) in a monitoring network of nine general stations and one roadside station in Hong Kong from 1998 to 2001. The territory-wide mean values for OC and EC in respirable suspended particulate matter (RSP or PM sub(10)) during this period are 8.89 and 4.66 mu g C/m, respectively. OC has a clear seasonal pattern with higher concentrations observed in the winter than in the summer at all the monitoring stations. The wintertime OC is two times of or higher than the summertime OC at each of the monitoring stations. Air masses of higher particulate loading enriched with OC transported from northern China are mainly responsible for the higher OC concentrations in the winter. To the contrary, the seasonality of EC is much weaker and variable among the monitoring sites. EC seasonality is found to depend on the distance from and relative location to the city's container port. A cluster of five stations to the immediately north of the container port have higher EC levels in the summer than in the winter as a result of being downwind of ship emissions in the summer, but upwind in the winter. EC concentrations at the three stations further north of the container port does not have discernable seasonality whereas EC at the two stations south of the port have the same seasonality as OC. The variable EC seasonality is a result of two counteracting factors, i.e. stronger influence of marine vessel emissions in the summer versus input of dirtier air masses in the winter. This also reveals that ship emissions at the port are important contributors to EC loadings in the air in Hong Kong. Further efforts are needed to characterize aerosol source profiles of ship emissions for quantifying their relative contributions to the ambient PM sub(10) in the city.