異戊二烯(Isoprene)為大氣中最常見且濃度相對較高的生物源揮發性有機化合物(Biogenic Volatile Organic Compounds， BVOCs)，具有高化學反應性，為都市臭氧生成的重要前驅物。然而，過去研究指出，都市環境中異戊二烯除生物源排放外，也會存在人為源排放，使其來源組成更加複雜，因此，若僅以總異戊二烯濃度進行分析，將難以了解不同來源對都市臭氧生成之相對影響。本研究以環境部光化學評估測站之萬華、忠明及小港站為研究對象，分析不同地區之都市環境中異戊二烯來源特徵及其對臭氧生成之影響。 本研究利用2014年至2023年冬季交通尖峰時段(07:00-08:00)異戊二烯與反式-2-戊烯之線性關係，估算人為與生物源異戊二烯濃度。結果顯示，異戊二烯來源具有明顯季節差異，夏季三測站生物源占比均超過80%；冬季因生物源排放降低，人為源貢獻增加，其中傳華站轉為以人為源為主，而忠明與小港測站仍以生物源為主要來源。此外，生物源異戊二烯與溫度呈現良好指數關係，其決定係數(R2)介於0.64至0.83，顯示溫度為控制生物源排放之主要因子。 為評估光化學反應對VOCs之影響，本研究利用光化學年齡法(Photochemical Age Method)回推VOCs初始濃度，並估算各物種光化學損失及其臭氧生成潛勢(Ozone Formation Potential， OFP)。結果顯示，夏季VOCs光化學損失明顯高於冬季，其中烯類為主要光化學損失來源，而生物源異戊二烯對OFP光化學損失之貢獻分別達50%、61%及20%，其在都市區域為重要的臭氧前驅物。此外，OFP光化學損失比例與臭氧濃度日變化具有高度一致性，夏季三測站相關係數均大於0.90，顯示VOCs光化學損失可有效反映臭氧生成特徵。 本研究進一步建立VOCs光化學損失與NOx之臭氧生成敏感性指標，結果顯示，萬華、忠明及小港測站分別有91.6%、72.4%及82.7%之數據位於VOC-limited區域，顯示都市臭氧生成多受VOCs控制。然而，隨著環境溫度升高，生物源異戊二烯的貢獻增加，VOCs光化學損失同步提升，使臭氧生成特徵逐漸朝向NOx-limited區域轉變，顯示高溫條件下生物源異戊二烯排放可能改變都市臭氧生成機制。;Isoprene is one of the most abundant biogenic volatile organic compound (BVOCs) in the atmosphere and， because of its high chemical reactivity， is an important precursor of urban ozone formation. However， isoprene in urban environments originates from both biogenic and anthropogenic sources， making its source composition more complex. Therefore， analyses based solely on total isoprene concentrations may not accurately represent the contributions of different sources to ozone formation. This study investigated isoprene source characteristics and their impacts on ozone formation using observations from the Wanhua， Chungming， and Xiaogang Photochemical Assessment Monitoring Stations in Taiwan. Anthropogenic and biogenic isoprene concentrations were estimated using the linear relationship between isoprene and trans-2-pentene during the winter morning traffic period (07:00–08:00) from 2014 to 2023. The results revealed distinct seasonal variations in isoprene sources. Biogenic isoprene accounted for more than 80% of the total isoprene at all three sites during summer. In winter， anthropogenic contributions increased because of reduced biogenic emissions. Anthropogenic isoprene became the dominant source at Wanhua， whereas biogenic isoprene remained dominant at Chungming and Xiaogang. In addition， biogenic isoprene exhibited a strong exponential relationship with air temperature， with coefficients of determination (R²) ranging from 0.64 to 0.83， indicating that temperature is the primary factor controlling biogenic isoprene emissions. To evaluate the effects of photochemical reactions on VOCs， the Photochemical Age Method was applied to estimate initial VOC concentrations and quantify photochemical losses and ozone formation potential (OFP). The results showed that VOC photochemical losses were substantially higher in summer than in winter. Alkenes contributed the largest fraction of VOC photochemical losses， while biogenic isoprene accounted for 50%， 61%， and 20% of the OFP loss at the Wanhua， Chungming， and Xiaogang sites， respectively， demonstrating that biogenic isoprene is a major ozone precursor in urban environments. Furthermore， the diurnal variation in the OFP loss ratio closely followed that of ozone concentrations， with correlation coefficients exceeding 0.90 at all three sites during summer， indicating that VOC photochemical loss effectively reflects ozone formation characteristics. Finally， ozone formation sensitivity was evaluated using the ratio of VOC photochemical loss to NOx. The results showed that 91.6%， 72.4%， and 82.7% of the observations at the Wanhua， Chungming， and Xiaogang sites， respectively， were classified as VOC-limited， indicating that ozone formation in urban areas is primarily controlled by VOCs. However， increasing air temperature enhanced biogenic isoprene emissions and VOC photochemical loss， shifting ozone formation toward the NOx-limited regime. These findings suggest that enhanced biogenic isoprene emissions under high-temperature conditions may alter ozone formation sensitivity in urban environments.
