|摘要: ||台灣光化學評估監測站自2002開始建立，到了2006年其運作方式才逐漸成熟，至今共有9個固定測站分佈在台灣西半部。光化學評估監測站網提供了以下的功能：1. 瞭解該區域臭氧前趨物的變化；2. 提供源與受體分析的資料庫；3. 驗證空氣品質模式的排放物種成份比例；4. 解釋高臭氧事件的原因及影響。為了達到上述四項功能，光化學評估監測站的資料必須經過嚴格的品保及品管作為以確保數據的品質。測站經過十年的運作及數據的累積，已經成為高價值的研究資料，可供使用者進行空污或健康之相關研究。本論文將針對下述兩項議題進行更深入的探討： |
由於異戊二烯是台灣地區最主要的生物源，而且和氫氧自由基具有相當高的反應性，因此，第三章以異戊二烯作為研究的主題。透過光化學評估監測站萬華站連續兩年的資料分析，發現異戊二烯的濃度變化是由生物源及交通源所共同貢獻的，為了將異戊二烯交通源貢獻分離出來，本論文使用乙烯作為交通排放的指標。研究中發現，嚴熱季節的中午之異戊二烯濃度逐漸攀升，特別是八月份，其最高平均濃度更高達1.6 ppbv，此時交通源的貢獻都被生物源的貢獻所掩蓋，但還是能在濃度峰的斜面上看到交通源的貢獻；而在寒冷季節的中午，則平均濃度降至0.2 ppbv，而且日夜變化和乙烯相似，主要為交通源的貢獻。本研究使用光化學評估監測站的異戊二烯資料，不但驗證了過去利用採樣罐分析的結果，而且其高時間解析的數據，更清楚地顯示由嚴熱季節至寒冷季節，生物源貢獻逐漸減少的變化過程。
本論文第四章利用光化學評估監測站十年來的資料進行趨勢分析，並且與空氣品質測站下降的趨勢結果互相驗證。由於資料數量龐大，不能單純使用多項式擬合的方式來求趨勢，因此採用美國海洋與大氣總署地球系統實驗室全球監測部的曲線擬合法，此方法被用來計算長生命期的二氧化碳濃度趨勢，本論文應用此方法來分析多個測站及多個物種的十年趨勢。首先在台灣北部地區、中部地區、南部地區挑選乙烯、丙烯、苯、甲苯、異戊二烯進行趨勢分析，其中前四個化合物是交通與工業的來源，而異戊二烯主要來自生物源。北部地區的萬華站，其上述的五種化合物均有下降的趨勢，特別是異戊二烯，其降幅更高達95.7%，研判與附近植被變化有密切關係。中部地區台西站，經過趨勢分析之後，發現丙烯和甲苯的降幅達到60%以上，而乙烯和苯有30%的降幅。南部地區的小港站，小港站，其上述的五種化合物均逐有下降的趨勢，其中又以乙烯的降幅達69%最為明顯。研判所觀察到的長期下降趨勢應與交通或工業相關之排放法規逐漸加嚴有密切關係。;The establishment of the network of Photochemical Assessment Monitoring Stations (PAMS) in Taiwan began in 2002, and majority of the stations were set up in 2006. Up to date, there are nine fixed sites across the west side of the island. The functionalities of the PAMS network are as follows: 1. to understand the abundance and variations of major ozone precursors in the regions; 2. to provide the database for source-and-receptor analysis; 3. to validate emission profiles for air-quality models; 4. to facilitate elucidating the cause-and-effect of high ozone episodes. In order to serve these four purposes, the PAMS measurements were subject to a strict protocol of quality control and assurance to safeguard data quality. Afterａdecade-long operation, the PAMS data have become an asset for users to explore its true values. Of many possible aspects that could be explored in depth, two were pursued to form the main themes of this thesis.
Isoprene was selected to be the subject of investigation from the PAMS database owing to its mostly biogenic nature, significant emissions on the island, and its extremely high reactivity to hydroxyl radicals. Inter-annual variations of atmospheric isoprene in Taipei were reported based on two years of PAMS data to reveal the detailed interplay between the biogenic and vehicular sources throughout the year. To separate the vehicular contribution from the biogenic one for the ambient isoprene, ethylene was used as an indicator of traffic emissions. While dramatic surge of isoprene was observed at noontime in hot months with the highest average peak mixing ratio of 1.6 ppbv in August, its abundance decreased to 0.2 ppbv on average in cold months. The vehicular contribution to ambient isoprene was largely masked over by the noontime surge of isoprene in hot seasons, but was still able to be vaguely observed on the slopes of the isoprene peaks mimicking the rush-hour features of ethylene. In winter, the diurnal variations of isoprene were very similar to those of ethylene, suggesting the traffic dominance in cold months. This work of isoprene with the use of the PAMS dataset greatly enhances the key findings in previous flask studies. Compared to flask sampling, the highly time-resolved PAMS data was intended to reveal the evolution process from a biogenically overwhelmed condition in hot months to the condition where the biogenic source weakened to reveal the traffic source in cold months.
The decade-long PAMS dataset from 2006 to 2015 allowed trend analysis to respond to the decline observed by the air quality stations. Due to the large size of the dataset, a curve-fitting algorithm adopted by National Oceanic and Atmospheric Administration (NOAA) used for long-lived trace gases such as carbon dioxide was applied to our trend analysis of multi-sites and multi-compounds. With the curve-fitting algorithm the dataset for each target compound was de-seasonized to reveal the decadal trend and residuals. Three sites in the north, central and south regions of Taiwan were selected for trend analysis of ethylene, propylene, benzene, toluene and isoprene. The first four compounds have common sources of vehicles and industries, whereas isoprene is largely biogenic. The Wanhua site in Taipei showed decreased trends for all the aforementioned compounds, with isoprene showing the most dramatic decline of 95.7% over the decade. A significant change in vegetation coverage should be the cause for such a pronounced decline in isoprene. In the central region, the Taixi site showed more than 60% declines for propylene and toluene, and more than 30% for ethylene and benzene. In the south region, the Siaogang site, which is in an urban-industrial hybrid environment, showed an overall decline for all these five compounds with the highest decline of 69% for ethylene. It is speculated that the declines were related to the ever tightening regulations on vehicular and industrial emissions in the past.