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Sewer construction in Taiwan lags other developed nations, and the authorities are undertaking major sewerage system construction projects in several cities. In Kaohsiung City, sewerage networks pass through residential, commercial and industrial areas. The composition of sewage thus is highly complicated. Eight target monitoring positions are chosen to analyze the compounds and concentrations of hazardous air pollutants. Pollutant concentrations are used to evaluate the cancer risk increment based on inhalation intake for sewer workers under using exhaust ventilation and wearing personal gas filtering equipment. GC/MS analysis confirmed that concentrations of benzene and trichloromethane compounds in sewer air for all the monitoring positions exceeded the minimum risk levels (MRLs) of 0.009 ppm benzene and 0.1 ppm trichloromethane, and the maximum concentrations reached 148.4 and 327.3 ppm, respectively. The cancer risks of benzene and trichloromethane for workers without personal protection approached 2.77-3.98 × 10 -3 and 29.74-42.70 × 10 -3 , respectively. Through ventilation for 15 minutes and the wearing of gas filtering equipment, the cancer risks for benzene and trichloromethane were reduced to 0.0003-0.0004 × 10 -3 and 0.0029-0.0041 × 10 -3 , respectively. The authorities thus must order all workers to follow a strict code of practice for sewer entry before entering sewer systems. This code of practice should include a minimum time for general exhaust ventilation and the use of personal protection equipment.

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[1] An air trajectory statistical approach was developed to estimate the relative contributions of various sources within a planning domain for a receptor site during high air pollution. The proposed approach is based on the coupling of residence time analysis and a known emission inventory. The theoretical basis of the approach is detailed. The approach was applied to investigate the relative contributions of various anthropogenic volatile organic compound (VOC) sources to the ozone formation potential of a receptor site in southern Taiwan. One hundred and ninety-seven ozone events (defined as those with an hourly ozone concentration that exceeded 120 ppb standard) over 1994-1998 were selected to undergo the residence time analysis. The VOC emission inventory was adjusted to reflect the different ozone formation potentials of the various sources by considering the source VOC profiles and the maximum incremental reactivity scales of each VOC compound. The results show that the sources that influenced the evaluated receptor site were located in northwestern coastal regions; the relative contributions of the point, line, and area sources were in the ration of approximately 5:2:3. Two districts, Kaohsiung City and Kaohsiung Hsien, were the dominant contributors of the five investigated districts. The proposed method may act as a preliminary tool to efficiently select the potential source region/category, such that mitigation and control strategies can be targeted, and/or used to guide a comprehensive modeling study.