With large primary emissions of nitrogen-containing compounds, wildfires impact the tropospheric oxidizing capacity, ozone (O₃), and formation of secondary organic and inorganic aerosol. The fate of reactive nitrogen in daytime fresh wildfire plumes was examined using airborne measurements over the western U.S. during the Wildfire Experiment for Cloud chemistry, Aerosol absorption, and Nitrogen (WE-CAN) campaign in the summer of 2018 together with a photochemical box model. For four wildfire plumes sampled in a pseudo-Lagrangian manner, the model predicts that the majority of emitted NO_x (96 ± 2%) is converted into peroxyacetyl nitrate (PAN) (27 ± 8%) and the sum of gas and particulate HNO₃ (29 ± 5%) within a few hours of plume evolution. In two of the plumes with the highest initial NO_x and HONO, the default model significantly underestimates the observed dilution-normalized decay rate of NO_x with plume age. We investigated several potential causes of this discrepancy and found that the model likely does not accurately represent the formation of a suite of oxidized organic nitrogen species such as alkyl and acyl peroxynitrates in these fire plumes, consistent with a suite of organic nitrogen compounds measured by chemical ionization mass spectrometry. This organic nitrogen reservoir can be similar in magnitude to that of PAN and thus represents an important fate of NO_x with uncertain impacts on downwind O₃ and aerosol nitrate formation depending on whether these are acyl peroxynitrates (APNs), alkyl nitrates (RONO₂), or nitro-aromatics.

中文翻译：

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新鲜野火羽流中 NOx 光化学和归宿的观察和建模

随着含氮化合物的大量初级排放，野火会影响对流层氧化能力、臭氧 (O ₃ ) 以及二次有机和无机气溶胶的形成。在 2018 年夏季的云化学、气溶胶吸收和氮野火实验 (WE-CAN) 活动期间，使用美国西部的空中测量以及光化学盒模型，研究了白天新鲜野火羽流中活性氮的命运。对于以伪拉格朗日方式采样的四个野火羽流，该模型预测大部分排放的 NO _x (96 ± 2%) 会转化为过氧乙酰硝酸盐 (PAN) (27 ± 8%) 以及气体和微粒 HNO ₃(29 ± 5%) 在羽流演变的几个小时内。在具有最高初始 NO _x和 HONO 的两个羽流中，默认模型显着低估了观测到的 NO _x稀释归一化衰减率随羽流年龄的变化。我们调查了造成这种差异的几个潜在原因，发现该模型可能无法准确地表示这些火羽中一系列氧化有机氮物质（例如烷基过氧硝酸盐和酰基过硝酸盐）的形成，这与通过化学方法测量的一组有机氮化合物一致。电离质谱。这种有机氮储库的量级与 PAN 的相似，因此代表了 NO _x的重要归宿，对顺风 O _{3 的}影响不确定和气溶胶硝酸盐的形成取决于它们是酰基过硝酸盐 (APN)、硝酸烷基酯 (RONO ₂ ) 还是硝基芳烃。