This paper reports the monitoring results of eleven polycyclic aromatic hydrocarbons (PAHs), four to six-ring, at two urban sites-Central & Western (CW) and Tsuen Wan (TW) in Hong Kong from January to December 2000; and the findings of a study conducted in 2001 of the partitioning of the gaseous and particulate phases of PAHs. The sum of the eleven PAHs under study (sigmaPAHs) was found to range from 6.46 to 38.8 ng m(-3). The annual mean levels at 12.2 ng m(-3) and 15.8 ng m(-3) for CW and TW respectively are comparable to those recorded for the previous two years and are also within the reported ranges for other metropolitan cities in the Asia Pacific region. Amongst the selected eleven PAHs, fluoranthene and pyrene were the two most abundant found in the urban atmosphere of Hong Kong during the study period accounting for approximately 80%, of the total PAHs. The ratios of benzo(a)pyrene to benzo(g,h,i)perylene (BaP/BghiP) and indeno(1,2,3-cd)pyrene to benzo(g,h,i)perylene (IDP/BghiP) indicate that diesel and gasoline vehicular exhausts were the predominant local emission sources of PAHs. Seasonal variations with high winter to summer ratios for each of the individual PAHs (CW: 1.6-16.7 and TW: 0.82-8.2) and for sigmaPAHs (CW: 1.9 and TW: 1.8) and a spatial variation of BaP amongst the air monitoring stations are noted. Results of correlation studies illustrate that local meteorological conditions such as ambient temperature, solar radiation, wind speed and wind direction have significant impact on the concentrations of atmospheric PAHs accounting for the observed seasonal variations. A snapshot comparison of the concentrations of PAHs at four sites including a roadside site, a rural site and the two regular urban sites CW and TW was also performed using the profiles of PAHs recorded on two particulate episode days in March 2000.

The results of a 12-month study of more than 100 solvent extractable organic compounds (SEOC) in particulate matter (PM) less than or equal to 2.5 m (PM 2.5 ) collected at three air monitoring stations located at roadside, urban, and rural sites in Hong Kong are reported. The total yield of SEOC that accounts for ϳ8 -18% of organic carbon (summer/winter differences) were observed with higher concentrations of the total and each class of SEOC in the winter and lower concentrations in the summer. Spatial variations are also obvious, with the roadside samples having the highest concentrations of SEOC and the rural samples having the lowest concentrations in all seasons. Characteristic ratios of petroleum hydrocarbons, such as carbon preference index, unresolved to resolved components, and carbon number with maximum concentration, suggest that PM 2.5 carbon in Hong Kong originates from both biogenic and anthropogenic sources. The proportion of SEOC in PM 2.5 from anthropogenic sources is estimated. INTRODUCTIONRecent concern about the health effects of air pollution has focused on suspended particulate matter or aerosols. Several studies 1-4 reveal links between the concentrations of suspended particulate concentrations and the mortality and morbidity of the exposed population. There has been some evidence that fine PM has greater impact on human health than do the coarser fractions. 5-8 Organic carbon (OC) has been widely reported 9 -11 to be a major component (over 40%) of fine suspended particles. Since the 1990s, studies have been carried out to identify and quantify the individual components of solvent extractable organic compounds (SEOC) in total suspended particulate (TSP), 12-17 PM 10 (particles with aerodynamic diameters less than 10 m), 18 -21 and PM 2.5 (particles with aerodynamic diameters less than 2.5 m). 22 Studies on the SEOC content and molecular markers in aerosols collected in China started in the early 1990s, as reported by Simoneit et al. 12 Fang et al. 13 first reported the content of SEOC in TSP samples collected in Hong Kong during the winter months of 1993. A study of the monthly average SEOC in PM 2.5 collected from the campus of the Hong

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