Photochemical Aging of Atmospheric Particulate Matter in the Aqueous Phase,Environmental Science & Technology

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Photochemical Aging of Atmospheric Particulate Matter in the Aqueous Phase
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2021-09-16 , DOI: 10.1021/acs.est.1c00978
Frank Leresche _{1,

2} , Joseph R Salazar ₃ , David J Pfotenhauer ₄ , Michael P Hannigan ₄ , Brian J Majestic ₃ , Fernando L Rosario-Ortiz _{1,

2}

Affiliation

This study focused on the photoaging of atmospheric particulate matter smaller than 2.5 μm (PM_2.5) in the aqueous phase. PM_2.5 was collected during a winter, a spring, and a summer campaign in urban and rural settings in Colorado and extracted into water. The aqueous extracts were photoirradiated using simulated sunlight, and the production rate (r_•OH) and the effects of hydroxyl radicals (^•OH) were measured as well as the optical properties as a function of the photoaging of the extracts. r_•OH was seen to have a strong seasonality with low mean values for the winter and spring extracts (4.8 and 14 fM s^–1 mg_C^–1 L, respectively) and a higher mean value for the summer extracts (65.4 fM s^–1 mg_C^–1 L). For the winter extracts, ^•OH was seen to mostly originate from nitrate photolysis while for the summer extracts, a correlation was seen between r_•OH and iron concentration. The extent of photobleaching of the extracts was correlated with r_•OH, and the correlation also indicated that non-^•OH processes took place. Using the ^•OH measurements and singlet oxygen (¹O₂) measurements, the half-life of a selection of compounds was modeled in the atmospheric aqueous phase to be between 1.9 and 434 h.

中文翻译：

水相中大气颗粒物的光化学老化

本研究侧重于水相中小于 2.5 μm (PM _2.5 )的大气颗粒物的光老化。PM _2.5在科罗拉多州城市和农村地区的冬季、春季和夏季运动期间收集并提取到水中。使用模拟阳光对水提取物进行光辐照，并测量产率 ( r _•OH ) 和羟基自由基 ( ^• OH) 的影响，以及作为提取物光老化函数的光学特性。r _•OH具有很强的季节性，冬季和春季提取物的平均值较低（4.8 和 14 fM s ^–1 mg _C^–1L）和夏季提取物的更高平均值（65.4 fM s ^–1 mg _C^–1 L）。对于冬季提取物，^• OH 主要来自硝酸盐光解，而对于夏季提取物，r _•OH与铁浓度之间存在相关性。提取物的光漂白程度与r _•OH相关，并且相关性还表明发生了非^• OH 过程。使用^• OH 测量值和单线态氧 ( ¹ O ₂) 测量，选定化合物的半衰期在大气水相中模拟为 1.9 至 434 小时。

更新日期：2021-10-06

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