自從台灣於2012年訂定細懸浮微粒周界標準以來，台灣的細懸浮微粒濃度每年都持續下降，代表細懸浮微粒管制策略的成效；但是臭氧濃度卻幾乎保持不變，特別是每日最高8小時平均值經常超過標準值。細懸浮微粒和臭氧的形成過程非常複雜，涉及多項前驅物物種與化學機制；例如氣相SO2 、NO2與揮發性有機物被氧化而分別生成固相硫酸鹽、硝酸鹽與有機氣膠，這些化學反應需要大氣中的氧化劑來促進，其中包括臭氧、H2O2和羥基自由基等；根據Pitts (2000)及Seinfeld (1998)書中所述，其主要反應有兩個循環所導致，分別為臭氧-氮氧化物滴定循環和揮發性有機物化合物氧化循環，故臭氧的生成與NOx和VOCs有關。
為了更好地了解PM2.5和O3之間的關係，本研究對2016、2019年台灣的測量數據和CMAQ模型的模擬數據進行了分析。本研究中針對主要的PM2.5水溶性組成成分硝酸根與硫酸根搭配模擬值的逐時濃度圖探討其形成機制，硝酸根形成主要由境內所產生，透過早上的NO2與O3反應形成的NO3 radical，在夜晚累積後與NO2反應形成N2O5，N2O5再與H2O形成HNO3，最後再與NH3形成NH4NO3，台灣硝酸根有南北差異主要為NH3的濃度所導致，南部地區NH3濃度高，因此在相同NO2下所形成的硝酸根較多；硫酸根的形成有2/3來源於境外的傳入，在境內部分主要透過SO2與H2O2在液相的反應形成，在上午5~8點間有峰值產生，其形成原因為溫度所導致，溫度越低H2O2的亨利常數越大，在液相中的H2O2的濃度上升形成更多硫酸根，導致峰值產生。了解硝酸根、硫酸根形成機制和臭氧形成機制後，參考Sillman (1995)臭氧敏感性H2O2/HNO3指標範圍0.35~0.6，了解台灣各地的臭氧敏感性，但在後續的模擬中發現其指標範圍可能不適用於台灣，本研究透過模擬分別只減量NOx或VOCs來觀察PM2.5和臭氧的濃度變化，得出NOx和VOCs的減量對於PM2.5的減量有正向影響，VOCs的減量對於臭氧的減量也是正向影響，但NOx的減量則需要謹慎管理有稍有不慎可能導致臭氧濃度上升，若想對NOx進行管制則應該搭配臭氧的濃度去做評估，並且至少要使OT下降20%以上才可以使O3_8hr的濃度會下降。

This study employs measurement data from Taiwan in 2016 and 2019, as well as simulated values from the CMAQ model, to dissect the formation mechanisms of nitrate and sulfate and gain insights into the influence of changes in NOx and VOCs on both PM2.5 and ozone via CMAQ simulations. Nitrate formation predominantly occurs within Taiwan, with the north-south variation attributed to NH3 concentration discrepancies. The southern region experiences higher NH3 levels, leading to heightened nitrate ion formation under equivalent NO2 conditions. External sources account for around two-thirds of sulfate ion generation, while domestic production is primarily driven by the liquid-phase reaction between SO2 and H2O2. Reducing NOx and VOCs exhibits a favorable impact on PM2.5 reduction, and curbing VOCs also demonstrates a positive effect on ozone reduction. However, the reduction of NOx necessitates cautious management, given the potential for elevated ozone concentrations. Should NOx control be pursued, a comprehensive evaluation in conjunction with ozone concentrations is imperative. Furthermore, achieving a substantial reduction of at least 20% OT (NO2 + O3) is essential to effect meaningful decreases in O3_8-hour concentrations.

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