Abstract:

In recent years, ozone pollution in the Pearl River Delta is getting worse. One of the key reasons is the nonlinear relationship between ozone and its precursor concentration; unbalanced precursor reduction may lead to an increase in ozone concentration. Therefore, research on the relationship between ozone and its precursors, as well as the sources of VOCs is of great significance for ozone pollution control. As a representative city of the Pearl River Delta city group, ozone pollution in Zhongshan is extremely serious. In this study, we launched a monitoring campaign in Zhongshan in September of 2020 and 2021, when ozone pollution is relatively severe. Five monitoring sites were selected to represent the air quality of Zhongshan, and both online and offline monitoring methods were used. The results showed that the average TVOC concentration on the Zimaling site in 2021 was 127.5 μg·m^-3, higher than that on the other sites, and increased by 5.2 μg·m^-3 since 2020, mainly due to the large increase of alkane quality concentration from 27.3 μg·m^-3 to 44.6 μg·m^-3；the quality concentration fluctuations of TVOC in September 2020 and 2021 were both significant and irregular, with overall high quality concentration levels in the middle and late stages. Ozone sensitivity analysis showed that ozone formation in Zhongshan City was VOC-limited in September 2020, while it was controlled by a transition regime in September 2021. According to the precursor reduction simulation, emission cut of NO_x and VOCs following a ratio of 1:3 or 1:2 would be a more conducive measure for ozone control. Analysis of ozone formation potential (OFP) at online and offline monitoring stations during the observation period showed that isoprene, m/p-xylene, toluene, o-xylene, 1, 2, 4-trimethylbenzene, and ethylene were the dominant species for ozone formation in Zhongshan City. Source apportionment results showed that vehicle exhaust and oil volatile were the largest sources of VOCs in Zhongshan City in both 2020 and 2021, accounting for 37.4% and 32.4%, respectively, while solvent use source was the largest source of OFP, accounting for 23.6% and 22.2% in 2020 and 2021, respectively. In summary, in order to effectively alleviate the ozone pollution in Zhongshan City, it is recommended to focus on the control of vehicle exhaust, oil volatile sources and solvent use sources.

Key words: ozone, precursor, ozone formation potential, EMKA curve, photochemical box model OBM, PMF model

摘要：

近年来，珠三角地区臭氧污染不断加剧，其重要原因之一在于臭氧与其前体物浓度之间存在非线性关系，不平衡的前体物削减会导致臭氧浓度不降反升，深入分析臭氧前体物与臭氧浓度之间的关系及解析VOCs的来源对于臭氧污染控制具有重要意义。中山市作为珠三角城市群的一个代表性城市，目前臭氧污染极其严重。选取当地5个站点，采取在线和离线两种监测方式，于2020年和2021年臭氧污染较严重的9月，开展臭氧前体物VOCs监测，并进行臭氧污染成因分析和VOCs来源解析。结果表明，2021年紫马岭站点的TVOC平均质量浓度达到127.5 μg·m^-3，高于其他站点，且同比上升5.2 μg·m^-3，主要原因是烷烃质量浓度从27.3 μg·m^-3大幅上升到44.6 μg·m^-3；2020年和2021年9月TVOC的质量浓度波动幅度均较大且不规律，中旬和下旬的整体质量浓度水平较高。臭氧敏感性分析表明，2020年9月中山市臭氧污染为明显的VOCs控制区，而2021年9月则为协同控制区。削减分析得出，结合中山市实际污染情况，灵活选择1:3或1:2的ρ_(NOx)/ρ_(VOCs)比例进行削减更有利于臭氧治理。观测期间在线和离线监测站点的臭氧生成潜势（OFP）分析显示异戊二烯、间/对-二甲苯、甲苯、邻-二甲苯、1, 2, 4-三甲苯、乙烯为中山市的臭氧污染优控物种。VOCs来源解析表明中山市2020年和2021年VOCs浓度贡献最大的来源均为机动车尾气及油品挥发源，分别占比37.4%和32.4%；OFP贡献最大的来源均为溶剂使用源，分别占比23.6%和22.2%。综上所述，为有效缓解中山市臭氧污染，建议重点对机动车尾气及油品挥发源和溶剂使用源进行控制。

关键词: 臭氧, 前体物, 臭氧生成潜势, EMKA曲线, 光化学箱模型OBM, PMF模型