| 英文摘要 |
This is an ongoing 3-year project, performed from 2005 to 2007. In the previous two years, characteristics of each VOC group and trends of selected compounds, indicators of photochemical air masses, diural variation, seasonal variation and acute hazard index, chronic hazard index and cancer risks had been thoroughly investigated. Therefore, the following abstract mainly summarizes the major findings of the third year.
The network of three photochemical assessment monitoring stations (PAMS) in central Taiwan havs been operated since 2003 to 2006. In 2006, the network in southern Taiwan and northern Taiwan also started to operate. Due to the increasing concern of pollutants from the largest petrochemical plant at the coast of south-central Taiwan, the three stations orignialy deployed in central Taiwan were relocated to the downwind areas of the plant, i.e. Yulin, ChiaYi, and Tainan Counties in the spring of 2007.
As for the stations in northern Taiwan, we developed a technique using PAMS data in Taipei to indicate frontal passages in the springtime. Air masses from long-distance transport were able to be accurately identified using the ratio of ethane/n-butane. During a frontal passage, it was found that ozone level is concurrent with the ratio, and the ozone level maintains as high as 40 ppbv with nighttime level similar to the daytime one, due to weak NOx titration. It poses a sharp contrast to the non-frontal days when ozone level peaks at noon time but drops to nearly zero at night due to strong NOx titration. Ethane/n-butane ratio at this time, however, was decoupled from the ozone cycle. Thus, the PAMS in Taipei can be exploited as a “whistle blower” for signaling the occurrence of cross border transport of air masses.
In this study, we analyzed the prilimiary results in 2007 and found that whenever the northterly winds prevaided, the concentrations of ethene and propolene increased dramatically, and can can be three to ten times higher at the Taishi station than at the urban Chungshan station. Futhre study will link these species of high activity to the contribution to ozone formation in south-central Taiwan.
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