| 英文摘要 |
The concentration of air pollutants were most likely affected by the land-sea breeze in central Taiwan. The mixing height is elevated by the westerly winds, which reach maximum values near noontime resulting in dissipation of pollutants. By contrast, the slower wind speeds in nighttime facilitate the build-up of ozone precursors. The formation of inversion layers at night is more pronounced in autumn than in summer rendering poorer vertical mixing and, hence, higher concentrations of precursors as well as ozone. In summer, the ratio of VOC/NOx is stable and it is more likely to fit in the characteristics of VOC-limited condition. In contrast, the ratio becomes more variable in fall, which is presumably induced by the unique meteorology associated with the fall season in central Taiwan. This instability in ratio in fall may partially explain the incoherence between ethylbenzene/xylene ratios and daily ozone peak values. This study also found that the majority of 56 target VOCs are released from motor vehicles. A second group of compounds, such as ethane, propane, and butane are originated from the leakage of liquefied petroleum gas (LPG) and natural gas. This study also investigated whether the some specific VOCs affect mortality. We combined continuous hourly data from PAM stations from 2002 to 2004 and also collected census and death data from governmental organizations. The results showed the the total natural mortality and cancer mortality in Taichung city were higher than in Nantou County, and this trend was similar with the concentration trend. Since the concentration is not as high as in occupational area, the long-term concentration data of these VOCs are recommended to be collected continuously in the future.
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