The extractable and non-volatile organic compounds in aerosol from urban (Kwun Tong, Kwai Chung, Mongkok, Central Western) and rural (Hok Tsui, HKUST) air in Hong Kong have been characterized qualitatively and quantitatively. The pollution sources have been revealed through the identification of the extractable and non-volatile organic pollutants, the study of component distributions and the determination of molecular markers....[ Read more ]

The extractable and non-volatile organic compounds in aerosol from urban (Kwun Tong, Kwai Chung, Mongkok, Central Western) and rural (Hok Tsui, HKUST) air in Hong Kong have been characterized qualitatively and quantitatively. The pollution sources have been revealed through the identification of the extractable and non-volatile organic pollutants, the study of component distributions and the determination of molecular markers.

Winter (December, 1993) and spring (April - May 1994) aerosol samples have been collected and analyzed. The samples were solvent extracted and fractionated by flash column chromatography into aliphatic hydrocarbon, PAH, aldehyde and ketone, fatty acid and fatty alcohol fractions. Each fraction was then analyzed by gas chromatography (GC) or gas chromatography-mass spectrometry (GC-MS). According to the CPI (carbon preference index), C_max (carbon number maximum), U:R ratio (unresolved:resolved components ratio) and LMWA/HMWA (lower molecular weight n-fatty acids to higher molecular weight n-fatty acids ratio) obtained, the organic pollutants from urban sites were confirmed to be originated mainly from petroleum residues in vehicle exhaust. About 40 species of PAHs have been identified in urban samples and their concentrations were found to be relatively high (0.01 - 5.88 ng/[cubic meter]), which suggested a need for a proper control strategy.

Novel organic pollutant discovery was another important objective for our study and the task involved the detection of trace level compounds, which is a challenge for analytical chemists. In the 2-propanol total extract of Mongkok aerosol sample, we have detected the presence of three novel aerosol-borne PAH-quinones, tentatively assigned as pyrene-1,12-dione, chrysene-5,6-dione and dibenzo[a,h]anthracene-7,14- dione, through the analytical results from gas chromatography-mass spectrometry (GC-MS), high performance liquid chromatography with UV diode array detector (LC-UV), liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS), liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry (LC-APCI-MS-MS). Also, we have confirmed our identification through the synthesis and analysis of standard compounds. The PAH-quinones have also been quantified with external standards by LC-APCI-MS. They were proposed to be produced through photochemical reactions from their parent-PAH in atmosphere or directly produced from petroleum combustion. These three PAH-quinones have not been reported in any aerosol study and are therefore considered as novel aerosol-borne pollutants. Among these, dibenzo[a,h]anthracene-7,14- dione is a novel compound with no record for its synthesis or presence.

A method for the analysis of aerosol-borne PAH by atmospheric pressure chemical ionization-mass spectrometry (APCI-MS) with flow injection has been developed. It possessed the advantages of fast analysis time and high selectivity for PAH species that simplified sample clean-up. The method also overcame the problem of GC-MS in the analysis of non-volative species. Eleven dominant PAH species in Hong Kong aerosol samples have been quantified with external standards by APCI-MS operated at the mode of selected ion monitoring (SIM) and the results were compared with those obtained by GC-MS. A significant discrepancy of the results from APCI-MS-SIM and GC-MS for higher molecular weight PAH was observed.

The last part of the thesis was concerned with the study of the dependence of unresolved:resolved ratio (U:R ratio) on gas chromatographic conditions. Because of the extensive use of this parameter in inter-sample comparison, we investigated the effect of different gas chromatographic conditions on the U:R ratio value. The aliphatic fraction of a Hong Kong rural aerosol sample was isolated by flash column chromatography from the corresponding organic extract. The fraction was then repeatedly analyzed by GC-MS using different GC temperature ramping rates, carrier gas linear velocities, sample injection volumes, and peak area integration thresholds. The U:R ratios so determined were found to be significantly dependent on the actual conditions employed. The value could range from 1.591 to 3.384, suggesting the substantial influence of instrumental conditions.