| 摘要: |
| 威海市属于我国北方典型沿海城市，近年来的持续观测发现夏季易出现臭氧（O3）污染。以2023年夏季观测数据为约束，利用零维盒子模式分析威海市夏季O3及大气氧化性特征，给出O3污染防治的建议。2023年5月30日—6月30日，威海市污染天的首要污染物是O3，烷烃是挥发性有机物（VOCs）中浓度占比最高的组分，烯烃则是活性占比最高的组分。从清洁日到污染日烯烃活性增强最显著，O3的化学生成和大气氧化性在污染日均有增加，促进了二次污染过程的发生。威海夏季大气氧化性水平较强，O3对前体物的敏感区处于氮氧化物（NO x ）和VOCs的过渡区，O3污染防控需结合NO x 和VOCs进行协同防控。O3对前体物烯烃减排的变化最敏感，因此其污染防控过程需结合VOCs反应活性开展。基于威海市夏季观测数据分析O3及大气氧化性特征，从O3敏感性区域变化及VOCs反应活性角度为O3污染防治策略提供了思路。 |
| 关键词: 威海 臭氧 大气氧化性 挥发性有机物（VOCs） VOCs反应活性 |
| DOI：10.7515/JEE232029 |
| CSTR：32259.14.JEE232029 |
| 分类号: |
| 基金项目:黄土与第四纪地质国家重点实验室开放基金（SKLLQG2218） |
| 英文基金项目:Open Fund of State Key Laboratory of Loess and Quaternary Geology (SKLLQG2218) |
|
| The characteristics of ozone and atmospheric oxidation capacity analysis in summer in Weihai |
|
ZHANG Feng, LI Kan, XU Zhaozhao, ZHANG Lingli, CHENG Chunlei, LI Jianjun
|
1. Weihai Ecological Environment Monitoring Center, Weihai 264200, China
2. Weihai Ecological Environment Affairs Service Center, Weihai 264200, China
3. Institute of Mass Spectrometry and Atmospheric Environment, Guangdong Provincial Engineering Research Center for On-line Source Apportionment System of Air Pollution, Jinan University, Guangzhou 510632, China
4. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
|
| Abstract: |
| Background, aim, and scope Ozone (O3) pollution has emerged as a significant concern for air quality in China, particularly as atmospheric fine particulate matter concentrations have declined in recent years. The complex formation of O3 is influenced by nitrogen oxides (NO x ) and volatile organic compounds (VOCs), as well as by meteorological conditions and regional transport. While numerous urban studies have probed O3 formation mechanisms, coastal cities like Weihai, which are influenced by both anthropogenic emissions and the marine environment, may exhibit distinct O3 formation pathways compared to inland urban areas. This study aims to identify the primary controlling factors and key precursors for O3 formation in such coastal city. Materials and methods The observational data were integrated with a chemistry box model to analyze O3 characteristics and atmospheric oxidation capacity (AOC) in Weihai. This study also evaluated the production and loss rates of O3, the relative increment reactivity (RIR) of major VOCs in O3 production, and explored O3 mitigation strategies through simulations of NO x and VOCs reduction. Results During the summer pollution episodes, O3 emerged as the predominant pollutant. The concentration of alkanes increased from 6.1 nmol·mol−1 to 9.1 nmol·mol−1, accounting for the majority of the ·OH reactivity, with a substantial contribution exceeding 60%. In contrast, aromatics and alkenes contributed 18.2% and 17.3%, respectively. The overall reactivity of VOCs with the ·OH rose from 3.9 s−1 during clean days to 4.6 s−1 on polluted days. Concurrently, the net production rate of O3 increased from 6.0 nmol·mol−1·h−1 in clean days to 7.4 nmol·mol−1·h−1 under polluted days. The AOC during the daytime O3 pollution period reached 6.0×10 sup>−17 mol·cm sup>−3·s sup>−1, surpassing the levels observed during clean days, which were 4.5×10−17 mol·cm−3·s−1. The investigation of relative increase reactivity (RIR) analysis showed that NO x was negative between 06: 00 and 10: 00, while the RIR of NO x became positive after 10: 00. In contrast, the RIR of VOCs remained positive throughout the day. Discussion The reactions of VOCs with ·OH were identified as the principal contributors to the AOC during daytime. This suggests that the heightened reactivity of diverse VOCs with ·OH may be an important factor influencing O3 production during pollution episodes. Analysis of ·OH reactivity revealed that alkenes and aromatics were the most significant contributors to O3 formation, with their reactivity toward ·OH escalating from clean to polluted conditions. Furthermore, the O3 production rate escalated during polluted days, predominantly attributed to the enhanced AOC. Elevated AOC levels in the summer, coupled with O3 existing in a transition sensitivity regime, imply that concurrent reduction of both NO x and VOCs could be beneficial for mitigating ozone pollution. Emission reduction simulations for various types of VOCs demonstrated that O3 was most sensitive to variations in alkene emissions, succeeded by aromatics and alkanes. This finding aligns with the previous analysis of the reactivity of VOCs with ·OH, reinforcing the notion that the formulation of O3 reduction strategies should prioritize the reduction of emissions based on the distinct reactivity profiles of VOCs with ·OH. This approach is more strategic than a blanket reduction of total VOCs concentrations. Additionally, the RIR value of NO x indicated that NO x emission abatement would be particularly beneficial for mitigating O3 levels in the afternoon when the photochemistry was the strongest in the daytime. Conclusions During the summer, O3 emerged as the primary pollutant on polluted days in Weihai, predominantly due to the intense local photochemical activity. Effective mitigation of O3 production could be achieved through the daytime control of VOCs and CO emissions, as the impact of NO x reduction on O3 formation was relatively minor in comparison to VOCs. Moreover, the control of O3 was found to be particularly sensitive to the reduction of alkene emissions. Consequently, mitigation strategies should be tailored based on a comprehensive assessment of O3 precursors, taking into account their varying contributions to O3 formation. Recommendations and perspectives O3 formation in urban areas is generally governed by VOCs emissions, with recent regulatory efforts primarily aimed at controlling VOCs emissions. This approach contrasts with the VOCs and NO x joint control strategy for O3 production observed in Weihai. The atmospheric environment of coastal cities, including factors such as relative humidity, temperature, and dilution conditions, differs from that of inland cities, and typically exhibits lower pollutant concentrations. These differences may account for the distinct dominant factors influencing O3 pollution in coastal versus inland urban areas. The findings of this study suggest that the mitigation of O3 pollution should be formulated based on the local meteorological conditions and emission profiles to develop effective reduction strategies. |
| Key words: Weihai ozone atmospheric oxidation capacity VOCs VOCs reactivity |
