Abstract:

Volatile organic compounds (VOCs) are key precursors of ozone (O₃) and secondary organic aerosols (SOA) and play a crucial role in urban air quality owing to their photochemical behavior in the atmosphere. However, traditional methods for assessing the environmental effects of VOCs based on measured concentrations (VOC_M) often underestimate photochemical losses. This study utilized NO⁺ PTR-QMS for high-time-resolution online monitoring of VOCs in Guangzhou University City during the of 2024 (August-October), overcoming the limitations of traditional PTR-MS in alkane detection. The results showed that during the observation period, the average volume fraction of atmospheric VOCs in Guangzhou was (29.0±0.73)×10⁻⁹, with alkanes (33.6%), aromatics (26.6%), and OVOCs (24.7%) being the main components. The 12h daytime variation in VOCs exhibited a bimodal pattern consistent with the morning and evening traffic peaks. The overall photochemical loss rate of VOCs (VOC_L) was as high as 22.3%, with the highest loss rate observed for alkenes (50.5%). After considering photochemical losses, traditional assessment methods based on VOC_M significantly underestimated the true environmental effects of VOCs: the Ozone Formation Potential (OFP_L) was underestimated by 35.5%, mainly driven by the highly reactive alkenes (butadiene 44.2%, butene 17.5%); the Secondary Organic Aerosol Potential (SOAP_L) was underestimated by 33.7%, mainly driven by high-SOA-yield aromatics (styrene 73.4%, C9/C8 aromatics). This study highlights that an accurate assessment of the environmental effects of VOCs requires consideration of photochemical loss. Prioritizing the control of highly reactive alkenes can effectively reduce O₃ formation, whereas controlling high-yield aromatics is key to reducing SOA pollution, which provides a scientific basis for the development of accurate VOCs emission reduction strategies and synergistic control of O₃ and PM_2.5 in Guangzhou City.

Key words: Guangzhou City, volatile organic compounds, photochemical loss, secondary pollutant formation potential, NO⁺ PTR-QMS

摘要： 挥发性有机物（VOCs）作为臭氧（O₃）和二次有机气溶胶（SOA）的关键前体物，其在大气中的光化学行为对城市空气质量影响至关重要。然而，传统基于观测体积分数（VOC_M）的环境效应评估方法因忽略VOCs的光化学损耗，往往导致其环境贡献被低估。于2024年8－10月在广州大学城采用NO⁺ PTR-QMS技术对VOCs进行了高时间分辨率的在线监测，克服了传统PTR-MS对烷烃检测的局限性。结果表明，观测期间广州市大气VOCs平均体积分数为（29.0±0.73）×10⁻⁹，主要组分为烷烃（33.6%）、芳香烃（26.6%）和OVOCs（24.7%），其日间变化呈现与早晚交通高峰活动一致的双峰型特征。VOCs的整体光化学损失率（VOC_L）高达22.3%，其中烯烃损失率最高（50.5%）。考虑光化学损失后，基于VOC_M的传统评估方法显著低估了VOCs的真实环境效应：臭氧生成潜势（OFP）被低估了35.5%，主要由高活性烯烃（丁二烯44.2%、丁烯17.5%）驱动；二次有机气溶胶生成潜势（SOAP）被低估了33.7%，主要由高SOA产率芳烃（苯乙烯73.4%、C9/C8芳香烃）驱动。研究强调，准确评估VOCs环境效应需考虑光化学损失，优先控制高活性烯烃可有效削减O₃生成，而控制高产率芳香烃是降低SOA污染的关键，这为广州市制定精准VOCs减排策略及O₃与PM_2.5协同控制提供了科学依据。

关键词: 广州市, 挥发性有机物, 光化学损失, 二次污染物生成潜势, NO⁺ PTR-QMS