Double High-Level Ozone and PM2.5 Co-Pollution Episodes in Shanghai, China: Pollution Characteristics and Significant Role of Daytime HONO
Double High-Level Ozone and PM2.5 Co-Pollution Episodes in Shanghai, China: Pollution Characteristics and Significant Role of Daytime HONO
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中国上海臭氧与PM2.5双重高浓度复合污染事件：白天HONO的污染特征及重要作用
DOI：
10.3390/atmos12050557
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发表时间：
2021-04
期刊：
影响因子：
2.9
通讯作者：
Wang Lin
中科院分区：
文献类型：
--
作者：
Yang Kejing;Kong Lingdong;Tong Songying;Shen Ji;ong;Chen Lu;Jin Shengyan;Wang Chao;Sha Fei;Wang Lin
近年来，上海地区不时出现细颗粒物（PM2.5）高污染和臭氧（O3）高污染事件。然而，它们的发生和特征仍然知之甚少。同时，HONO作为对流层羟基自由基（OH）的主要前体，启动氢过氧自由基和有机过氧自由基的形成，不可避免地会影响O3的形成，但在PM2.5和O3双高污染时期，其在O3形成中的作用尚不清楚。通过2014 - 2016年上海城市双高污染期的野外观测，研究了双高污染期的特征及HONO在双高污染期O3形成中的作用。结果表明：PM2.5高污染与O3高污染可能同时发生；O3和PM2.5双高的病例约占整个采样周期的1.0%。双高污染期仍存在活跃的光化学过程，而高PM2.5浓度下的活跃光化学过程在voco限制和高温、中高相对湿度、低风速的平静大气条件下有利于O3的产生和积累；进而促进了SO2和NO2的转化，以及二次硫酸盐和硝酸盐气溶胶的形成和积累，进一步促进了PM2.5浓度的升高和大气污染的恶化。进一步分析表明，在大部分双高污染时段，白天HONO浓度与O3浓度呈显著负相关，表明在双高污染时段，HONO在O3形成中起主导作用。本研究为了解白天HONO对O3形成的重要贡献提供了重要的野外观测证据，有助于阐明O3和PM2.5双高污染事件的形成和共存机制。
In recent years, high fine particulate (PM2.5) pollution episodes with high ozone (O3) levels have been observed in Shanghai from time to time. However, their occurrence and characteristics remain poorly understood. Meanwhile, as a major precursor of tropospheric hydroxyl radical (OH) that initiates the formation of hydroperoxyl and organic peroxy radicals, HONO would inevitably affect the formation of O3, but its role in the formation of O3 during the double high-level PM2.5 and O3 pollution episodes remains unclear. In this study, the characteristics of the double high pollution episodes and the role of HONO in O3 formation in these episodes were investigated based on field observation in urban Shanghai from 2014 to 2016. Results showed that high PM2.5 pollution and high O3 pollution could occur simultaneously. The cases with data of double high O3 and PM2.5 concentrations accounted for about 1.0% of the whole sampling period. During the double high pollution episodes, there still existed active photochemical processes, while the active photochemical processes at high PM2.5 concentration were conductive to the production and accumulation of O3 under a VOC-limited regime and a calm atmospheric condition including high temperature, moderately high relative humidity, and low wind speed, which in turn enhanced the conversions of SO2 and NO2 and the formation and accumulation of secondary sulfate and nitrate aerosols and further promoted the increase of PM2.5 concentration and the deterioration of air pollution. Further analysis indicated that the daytime HONO concentration could be strongly negatively correlated with O3 concentration in most of the double high pollution episodes, revealing the dominant role of HONO in O3 formation during these pollution episodes. This study provides important field measurement-based evidence for understanding the significant contribution of daytime HONO to O3 formation, and helps to clarify the formation and coexistence mechanisms of the double high-level O3 and PM2.5 pollution episodes.
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