An investigation of volatile organic compounds in urban area of Hong Kong by using canister and GC/MS

Abstract

The project aims to identify, quantify and characterize volatile organic compounds (VOCs) in different urban areas in Hong Kong by conducting field surveys. This project involves the spatial distribution, temporal variation as well as vertical profile of VOCs at roadside microenvironment at five sampling locations. There were 12 VOCs commonly detected in urban areas (Mong Kok, Kwai Chung, Yuen Long and Causeway Bay). Benzene, toluene, ethylbenzene and xylenes (BTEX) were the major composition of VOCs in urban air (more than 60% in composition of total VOC detected), where mobile sources were the main sources of these pollutants. Similar to other Asian cities, the VOC levels measured in urban areas in Hong Kong were affected both by automobile exhaust and industrial emissions. There were mainly two types of sources, mobile sources and stationary sources affecting the urban areas. Thus, high toluene to benzene ratios (T/B) was also found in Hong Kong as in other Asian cities. In general, VOC concentrations in the winter were higher than those measured in the summer. Diurnal variation cannot be observed in this study. Vertical profiles of VOCs followed power law and their asymptotic values of BTEX were reached 52 m height above the ground that implicated that stabilized dispersion concentration or the ambient concentration can be measured at this level. The 24-hour monitoring station was established to monitor daily variation, temporal variation and seasonal variation of VOCs. Daily variations of VOCs showed that the traffic data was consistent with the variations of the concentrations of benzene, ethylbenzene and xylenes. The highest monthly average concentrations of most of VOCs were recorded on March 2000 due to the highest API recorded at that month. VOC concentrations measured in the summer were higher than those in the winter due to the meteorological factor and site location. The cancer risk assessment were carried out based on the 95% confidence levels of the four carcinogenic VOCs including 1,3-butadiene, benzene, methylene chloride and chloroform for 1 hour daily exposure. The highest cancer risk of 7.87 10-5 was associated with the pedestrians who were exposed to 1,3-butadiene in Mong Kok and the highest total cancer risk of 8.85 10-5 was also found in Mong Kok. 1,3-Butadiene and benzene were the major pollutants from vehicle exhausts. Thus, it is necessary to control the emission of both compounds by setting tight automobile emission standards in Hong Kong.