Anthropogenic Control Over Wintertime Oxidation of Atmospheric Pollutants
Anthropogenic Control Over Wintertime Oxidation of Atmospheric Pollutants
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DOI：
10.1029/2019gl085498
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发表时间：
2019-12-20
影响因子：
5.2
通讯作者：
Thornton, J. A.
中科院分区：
文献类型：
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作者：
Haskins, J. D.;Lopez-Hilfiker, F. D.;Thornton, J. A.
在中纬度地区的冬季，光化学氧化明显慢于夏季，并且由于缺乏该季节的观测，导致细颗粒物和臭氧等二次污染物形成的主要自由基氧化剂仍不确定。利用空气观测，我们量化了冬季区域内各种氧化剂的贡献，从而改进了冬季空气污染转变的化学描述。我们发现，25-60% 的 NOx 通过气相氮氧化物库和气溶胶颗粒之间的多相反应转化为 N2O5，其中 93% 在海洋边界层中发生反应，形成 >2.5 ppbv ClNO2。这导致冬季污染空气的氧化能力超过 70% 由多相反应和挥发性有机化合物（如 HCHO）的排放控制，而不是与 OH 反应。这些发现强调了当地人为排放对受污染的冬季大气氧化能力的控制。 通俗易懂的语言摘要在夏季，直接排放到大气中的主要污染物迅速转化为二次污染物，如颗粒物和臭氧，这是由与羟基自由基的反应驱动的，羟基自由基是在水蒸气存在的情况下阳光照射到大气中时形成的。在冬季，阳光和水蒸气较少，这种自由基的产生量较低。然而，初级污染物向次级污染物的转化仍然迅速发生，这表明对冬季推动这种转化的化学过程存在误解。利用 2015 年冬季在美国东北部收集的飞机数据，我们发现与硝酰氯等非典型前体产生的自由基的反应占直接排放污染物发生的反应的 70% 以上。我们表明，在冬季，这些自由基的形成与人类活动有关。我们的数据为改进空气质量模型中化学过程的描述提供了关键约束，这将有助于指导改进的空气质量政策。世界其他地区，如中国、欧洲和印度北部，也经历着大气中的这种季节性化学变化。因此，我们的研究结果对于理解冬季污染转化和运输具有全球范围的影响。
During winter in the midlatitudes, photochemical oxidation is significantly slower than in summer and the main radical oxidants driving formation of secondary pollutants, such as fine particulate matter and ozone, remain uncertain, owing to a lack of observations in this season. Using airborne observations, we quantify the contribution of various oxidants on a regional basis during winter, enabling improved chemical descriptions of wintertime air pollution transformations. We show that 25-60% of NOx is converted to N2O5 via multiphase reactions between gas-phase nitrogen oxide reservoirs and aerosol particles, with similar to 93% reacting in the marine boundary layer to form >2.5 ppbv ClNO2. This results in >70% of the oxidizing capacity of polluted air during winter being controlled by multiphase reactions and emissions of volatile organic compounds, such as HCHO, rather than reaction with OH. These findings highlight the control local anthropogenic emissions have on the oxidizing capacity of the polluted wintertime atmosphere.Plain Language Summary During summer, rapid transformations of primary pollutants, those emitted directly into the atmosphere, into secondary pollutants, such as particulate matter and ozone, are driven by reactions with the hydroxyl radical, formed in the atmosphere when sunlight strikes ozone in the presence of water vapor. During winter, when there is less sunlight and water vapor, production of this radical is lower. Yet the conversion of primary pollutants into secondary pollutants still occurs rapidly, pointing to a misunderstanding in the chemical processes that drive this conversion during winter. Using aircraft data collected across the northeast United States during the winter of 2015, we show that reactions with radicals arising from atypical precursors, such as nitryl chloride, account for more than 70% of the reactions that directly emitted pollutants undergo. We show that during winter, the formation of these radicals is tied to human activities. Our data provide critical constraints for improving the descriptions of chemical processes in air quality models, which will help guide improved air quality policy. Other regions of the world, such as China, Europe, and northern India, also experience this seasonal chemical shift in the atmosphere. Our findings, therefore, have global scale implications for understanding wintertime pollution transformations and transport.