| 摘要: | 近年來，隨著環保法規的日益完善，台北盆地地區的空氣污染物整體呈現下降趨勢。然而，長期觀測資料顯示，每年仍有少數幾天出現高污染事件，PM₁₀、PM₂.₅、NMHC、NO、CO、CH₄ 等一次污染物在短時間內大量累積。為深入探討這類事件的成因與影響，本研究整合自製總碳氫分析儀、台北市環保局測站、中央氣象局探空氣球資料，以及環境部光化測站之十年數據，系統性分析台北地區高污染事件的特徵與成因。
本研究以實驗室自製總碳氫偵測器為核心，該儀器設置於交通繁忙的台北市南京東路，可即時測量周遭環境中的 NMHC 與 CH₄ 濃度，自投入運作以來已累積三年觀測資料。2024 年 3 月 5 日，儀器觀測到一次極端高濃度事件，CH₄ 與 NMHC 分別上升至 3.8 ppm 與 0.9 ppm，約為日常平均值的 1.9 倍與 4.5 倍。進一步比對台北地區多個測站資料發現，此次事件為整個台北盆地範圍內的同步現象。結合風速風向逆推軌跡與探空氣球斜溫資料判斷，事件主因為輻射逆溫造成污染物無法擴散，進而異常累積。
鑑於此事件的代表性，我們開始系統蒐集並分析台北地區歷年高值污染事件。由於自製儀器觀測時程僅三年，本研究進一步引用環境部中山測站 2013 至 2023 年的總碳氫與其他污染物數據，並以甲烷的常態分布計算方式，將超過三個標準差（> 99.73%）的數值定義為異常高值事件。結果顯示，約有90.2% 的異常高值事件與逆溫現象有關，且可細分為輻射逆溫（34.9%）、沉降逆溫（28.7%）及鋒面逆溫（26.7%）。除臭氧外，所有一次污染物皆呈現高度累積現象。此外在逆溫條件下，過量的 NO 與臭氧發生滴定反應，導致臭氧濃度顯著下降。
接著，我們引用環境部光化測站(PAMS)監測的 54 種碳氫化合物資料，發現在逆溫期間除 isoprene 外，所有化合物的平均濃度皆上升約 2 至 3 倍。進一步將濃度轉換為百分比濃度後發現，逆溫期間與整體平均值相近，顯示在大氣靜滯條件下，光化反應速率下降，污染物以較均勻方式逐漸累積。為探討污染氣團的新鮮程度，我們引入氣團老化指標，利用丁烷與戊烷的生命週期差異進行分析，並將逆溫高值時間對應結果發現：春冬季的輻射逆溫常與較新鮮氣團相對應，鋒面逆溫多發生於老化氣團，而沉降逆溫則呈現較分散的類型，結果與大氣動力預期相符。
研究第二部分探討總氧化劑（O₃ + NO₂）與非甲烷揮發性有機物（NMHC）間的交互關係，藉此理解近地表臭氧生成機制。分析中，我們以 Ethylbenzene 與 m,p-Xylene 比值（E/X ratio）為氣團老化指標，探討其與總氧化劑濃度的關聯性，發現二者在穩定大氣條件下呈正相關。進一步根據不同物種的光化學反應活性推估其消耗濃度並加總後，結果顯示總氧化劑濃度與 NMHC 總消耗量之間具有顯著正相關（如土城站 R² = 0.48，萬華站 R² = 0.50），顯示 NMHC 為近地表臭氧生成的重要前驅物。
綜合上述結果，台北盆地之異常高值事件多與逆溫有關，使一次污染物大量累積至極高濃度，而不同類型的逆溫對污染物累積與氣團老化程度影響各異，進一步突顯大氣穩定度在區域空氣品質控制中的關鍵性。此外，光化學資料亦證實 NMHC 與總氧化劑間具有明確關聯性，顯示減少 NMHC 排放對於有效控制地表臭氧濃度具有策略性重要性。
;Abstract
In recent years, stricter environmental regulations have led to a general decline in air pollutants across the Taipei Basin. However, long-term data show that several high pollution events still occur occasionally, during which primary pollutants such as PM₁₀, PM₂.₅, NMHC, NO, CO, and CH₄ rapidly accumulate. To examine their causes and impacts, this study integrates data from a laboratory-built total hydrocarbon analyzer, measurements of other pollutants from multiple Taipei EPA air-quality monitoring stations (AQMS), upper-air sounding data from the Central Weather Bureau, and a decade of photochemical assessment monitoring stations (PAMS) records.
At the core of this study is our laboratory-built hydrocarbon analyzer installed on busy Nanjing East Road in Taipei. It provides real-time NMHC and CH₄ measurements for three years. On March 5, 2024, an extreme event was recorded: CH₄ and NMHC levels spiked to 3.8 ppm and 0.9 ppm, about 1.9 and 4.5 times the daily averages. Comparisons across all Taipei AQMS confirmed a basin-wide phenomenon. Wind trajectory and sounding data suggested a radiation inversion as the main cause, trapping pollutants and causing abnormal accumulation.
Given the event’s representativeness, we systematically analyzed historical high-pollution episodes. As the custom analyzer covers only three years, we used 2013–2023 data from Zhongshan AQMS station. Abnormally high CH₄ values were defined as exceeding three standard deviations above the mean (>99.73%). About 90.2% of such events were linked to inversions: radiation inversions (34.9%), subsidence inversions (28.7%), and frontal inversions (26.7%). All primary pollutants—except ozone—showed strong accumulation. Inversion conditions also led to NO-ozone titration reactions, significantly reducing ozone levels.
Subsequently, we analyzed 54 hydrocarbons from a PAMS station at Tucheng. During inversions, all compounds (except isoprene) rose by 2–3 times. Their normalized concentrations stayed similar to long-term averages, indicating reduced photochemical activity and gradual accumulation under stagnant conditions. To assess the aging conditions of air masses, we used the butane/pentane ratio. Results showed radiation inversions (in winter and spring) were linked to fresher air, frontal inversions to older air, and subsidence inversions to mixed types—consistent with atmospheric dynamics.
In the second part, we explored the interaction between total oxidants (O₃ + NO₂) and NMHCs to understand near-surface ozone formation. The ethylbenzene to m,p-xylene ratio (E/X) was used as an aging indicator and showed a positive correlation with oxidants under stable conditions. By estimating and summing species-specific NMHC losses based on reactivity, we found strong correlations between oxidant levels and NMHC depletion (e.g., R² = 0.48 at Tucheng, R² = 0.50 at Wanhua), indicating NMHCs are key ozone precursors.
In summary, most abnormal high-pollution events in Taipei are tied to inversion layers, which cause significant pollutant buildup. Different inversion types influence accumulation and air mass aging differently, underscoring the role of atmospheric stability in regional air quality control.The PAMS data confirm NMHCs are closely linked to total oxidants, highlighting the strategic importance of reducing NMHCs to manage surface ozone. |
