Carbonaceous characteristics of atmospheric particulate matter in Hong Kong

Abstract

To determine the characteristic of carbonaceous species in atmospheric particles in Hong Kong, PM 10 and PM 2.5 samples were collected using high volume (hi-vol.) air samplers from November 2000 to February 2001. The organic carbon (OC) and elemental carbon (EC) were analyzed by the selective thermal manganese dioxide oxidation (TMO) method. The ratios of PM 2.5/PM 10 mass ratios were 0.61, 0.78 and 0.53 for particulate matter collected at PolyU station (PolyU, near a major traffic corridor), Kwun Tong station (KT, mixed residential/commercial/industrial) and the Hok Tsui background station (HT), respectively. These results indicate that the PM 2.5 concentrations constitute the majority of the PM 10 concentrations, especially in urban and industrial areas of Hong Kong. The average concentrations at the three sites ranged from 73.11 to 83.52 μg/m 3 for PM 10 and from 42.37 to 57.38 μg/m 3 for PM 2.5. The highest daily mass concentrations of PM 10 and PM 2.5 were 125.89 μg/m 3 and 116.89 μg/m 3 at KT, respectively. The correlation between PM 10 and PM 2.5 was high at KT and HT ( r>0.9, P<0.01). This means that the sources of PM 10 and PM 2.5 may be the same at both sites. The highest mean concentration of OC (12.02 μg/m 3) and EC (6.86 μg/m 3) in PM 10 was found at the PolyU among the three sites. For PM 2.5, the highest mean concentration of OC (10.16 μg/m 3) was at KT while the highest mean concentration of EC (7.95 μg/m 3) was at PolyU. However, the background concentrations at HT were higher than another background area, Kosan, Korea. Transportation of pollutants from the Asian continent may be responsible for the elevations of EC+OC at the remote site. More than 74% of the EC and more than 79% of the OC were found in the PM 2.5 fraction at the three sampling locations. At PolyU station, PM 2.5 consisted of 18.18% OC and 11.16% EC while 17.70% OC and 8.81% EC were found in KT station. Thus OC and EC are major constituents of aerosols in Hong Kong. OC/EC ratios for PM 10 and PM 2.5 were less than 2 at PolyU and KT stations while the ratio exceeded 3 at HT background station. This indicates that OC measured in the urban area may be emitted directly as a primary aerosol.