| 摘要: | 臭氧污染為「區域性的問題」，從前驅物VOCs及NOx之排放經光化學反應到臭氧產生與累積的尖峰通常差距2~6小時，在此時間內前驅物及臭氧易受到風的影響而傳輸至下風處，因此臭氧污染的影響範圍往往擴及都會區或工業區之下風郊區。但由於不同都會區VOCs、NOX來源及排放的特性(種類與強度)不同，且氣候、地形條件存在著很大的差異，因此在臭氧生成方面也有很大的不同及變異。
近地表臭氧為多數先進國家檢視空氣汙染的重點指標之一(Pollutant standard index, PSI)，與懸浮微粒同存影響國內空氣品質最顯著的汙染物。近地表臭氧為二次汙染物，為前驅物質NOX和揮發性有機化合物(Volatile organic compounds, VOCs)經由光化反應而生成，但VOCs的種類繁多，且各物種對於臭氧生成的貢獻有所差異，因此在不同環境下，其臭氧生成的機制與特徵也隨之變化。在此選擇桃園地區進行觀測實驗，以即時觀測搭配採樣的方式，分析55種VOCs物質，以探討該地區近地表臭氧的來源，可作為訂立排放管制政策的參考。
桃園地區的VOCs排放結構較為複雜，涵蓋了交通源及工業源兩類，研究中發現交通源中之乙烯、丙烯、1, 2, 4-三甲基苯對於臭氧生成的貢獻較為顯著，相較於此，工業源的OVOC比例亦相當明顯，說明了該地區為複合型的VOCs排放特性。而藉由PTR-MS的觀測，獲得工業區的乙醛(acetaldehyde)濃度變化趨勢，本研究並引用各VOCs的最大增量反應性(Maximum incremental reactivity, MIR)加以計算，求得各VOCs物種的臭氧生成潛勢，並證實了醛類為該地區臭氧生成的重要物質之一。
為求了解醛類與各VOCs貢獻生成臭氧的重要性，藉由模式模擬來統整桃園地區之醛類排放量分佈情形，並輔助說明傳輸與化學機制過程，來剖析這些前驅物對於臭氧生成的貢獻量與影響的幅員範圍。觀測數據與模式模擬相輔相成，有助於全貌了解桃園地區臭氧生成，進而提供適切的管制策略，改善當地空氣品質。
Near-surface ozone is one of the key pollutants in most countries. Ozone is a secondary pollutant produced from photochemistry. It is formed via reactions involving NOX and volatile organic compounds (VOCs) in the presence of sunlight. NOx and VOCs together are called “ozone precursors”. Therefore, the abatement of precursors at minimum social and economical cost will be the key to reduce surface ozone and to improve air quality. However, VOCs are a collective term composing hundreds of thousands of airborne compounds with a wide range of ozone formation potentials (OFPs). As a result, it is not only economically viable but also sensible to only target species of high OFPs and abundance.
VOCs emissions in the Taoyuan area consist of two major sources of traffic and industrial emissions. As a key part of a collective field campaign aiming at reducing ozone in Taoyuan county, an on-line VOCs monitoring system was set up in Taoyuan city during 9/14/2012 - 11/23/2012 to investigate the composition and levels of more than 50 VOCs in a traffic ridden environment with hourly resolution. Moreover, off-line flask sampling in seven surrounding industrial parks was also performed to shed light to VOCs of industrial nature.
Two methods of maximum incremental reactivity (MIR) and relative consumption were used to reveal the critical VOCs to form ozone. High OFP VOCs such as propylene, ethylene and 1,2,4-trimethylbenzene were found to be significant with the city measurements. In the industrial parks, high levels of oxygenated VOCs (OVOC), especially acetaldehyde were observed. In one example (中壢工業區), OVOC can contribute more than 70% of the total VOCs level, and acetaldehyde alone can contribute as high as 80% in ozone formation. As a result, the role of ambient aldehyde as a primary pollutant and its possible removal from the industrial processes due to its strong OFP and toxicity is worth investigation. |
