臭氧（O3）是空氣中重要的組成部分，在大氣中作為氧化劑起著重要作用。在地表中臭氧被視為二次空氣污染物，而地表的臭氧會對人類健康和生態系統造成嚴重的不利影響，其形成和累積主要是通過紫外線對二氧化氮進行光解所產生的，因此在夜間沒有陽光的情況下不應該存在高臭氧濃度，本研究的目的是統計2016及2019年全台各測站夜間臭氧峰值頻率並探討其成因及參考比較國外文獻夜間臭氧的機制來了解台灣地區夜間臭氧形成與國外案例的差異。
本研究首先挑選出2016及2019年臭氧八小時AQI大於150事件日，針對事件日中的臭氧逐時濃度進行夜間峰值特性分析，分析方法為使用當日環保署監測之臭氧逐時濃度數值分析日夜變化趨勢圖，並由趨勢圖判別夜間臭氧峰值時間點，應用WRF氣象場資料模擬三維氣象場，再以HYSPLIT回推24小時的三維軌跡線，最後搭配Surfer推估軌跡線上峰值發生前之臭氧與其前驅物之逐時濃度。並加入文獻中臭氧峰值形成的機制將其分成三種特性，垂直傳輸型、水平傳輸型及在地形成型，在地形成型將設計實驗利用夜間NO2及NO3 Radical光解形成臭氧來解釋，最後整理出夜間臭氧峰值發生時各測站污染物濃度及氣象條件來了解峰值發生時的環境因素。
由統計結果來看2016年北部空品區發生夜間臭氧峰值發生站次為全台最多，其次是高屏空品區；而2019年以高屏空品區夜間臭氧峰值發生站次為全台最多；各縣市統計中，2016年各縣市夜間臭氧峰值發生比例以新竹市發生比例最高，其次是新竹縣，在各監測測站中以湖口、潮州及左營等測站發生比例最高；而2019各縣市夜間臭氧事件發生比例則以高雄市發生比例最高，其次是新竹市，在各監測測站中以林園、左營及安南等測站發生比例最高。本研究將夜間峰值分類成三種特性，分別為垂直傳輸、水平傳輸及在地生成案例，由2016年統計結果在臭氧八小時AQI大於150的夜間發生臭氧峰值案例94站次中，垂直傳輸型有20站次；水平傳輸型有29站次；在地生成型有45站次；而2019年統計結果在臭氧八小時AQI大於150的夜間發生臭氧峰值案例63站次中，垂直傳輸型有3站次；水平傳輸型有20站次；在地生成型有35站次。在地形成型案例通過CMAQ模擬NO3濃度及軌跡線上NO2平均濃度搭配本研究光譜儀檢測光源計算結果得出NO2及NO3於在地形成型案例中光解形成臭氧總量，在2016年各案例軌跡線上平均上升18.3 ppb；2019年平均上升11.1 ppb，但皆分別小於2016年與2019年軌跡線上變化量，顯示本研究的計算整體上有低估的情形，但透過實驗也證實了NO2及NO3於夜間經過可見光光解在地形成臭氧的機制。
而當臭氧峰值出現在夜間時，在三種類型中都有觀察到測站當下的NOx濃度皆低於該時間點的年平均值。因此，2016及2019年夜間峰值出現的原因為垂直傳輸、水平傳輸及NO2及NO3光解在地形成，並由於峰值發生當下NOx濃度皆低於平均值，導致臭氧沒有辦法因為與NOx反應而被消耗。

This study analyzes the nocturnal ozone peaks of the daily maximum ozone 8-hour-average air quality index greater than 150 events in Taiwan and uses HYSPLIT-model to perform back-trajectory analyses in 2016 and 2019 to estimate the concentration variations within air parcel along trajectory. The formation mechanisms of nocturnal ozone peaks are classified into three types: vertical transport, horizontal transport, and in-situ NO2 and NO3 photolysis. The statistical results show that the percentages for the occurrence of ozone peaks at night for vertical transport, horizontal transport, and in-situ NO2 and NO3 photolysis are 21%, 31%, and 48%, respectively, in 2016 and are 5%, 32%, and 56%, respectively, in 2019. Therefore, the in-situ NO2 and NO3 photolysis has the largest proportion and followed by horizontal transport. NO concentrations duration ozone peaks are generally lower than the average, implying that ozone is not consumed by NO titration. There is no way for ozone to be consumed by reacting with NOx.

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