Reactive nitrogen (N_r) within smoke plumes plays important roles in the production of ozone, the formation of secondary aerosols, and deposition of fixed N to ecosystems. The Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE‐CAN) field campaign sampled smoke from 23 wildfires throughout the western U.S. during summer 2018 using the NSF/NCAR C‐130 research aircraft. We empirically estimate N_r normalized excess mixing ratios and emission factors from fires sampled within 80 min of estimated emission and explore variability in the dominant forms of N_r between these fires. We find that reduced N compounds comprise a majority (39%–80%; median = 66%) of total measured reactive nitrogen (ΣN_r) emissions. The smoke plumes sampled during WE‐CAN feature rapid chemical transformations after emission. As a result, within minutes after emission total measured oxidized nitrogen (ΣNO_y) and measured total ΣNH_x (NH₃ + pNH₄) are more robustly correlated with modified combustion efficiency (MCE) than NO_x and NH₃ by themselves. The ratio of ΣNH_x/ΣNO_y displays a negative relationship with MCE, consistent with previous studies. A positive relationship with total measured ΣN_r suggests that both burn conditions and fuel N content/volatilization differences contribute to the observed variability in the distribution of reduced and oxidized N_r. Additionally, we compare our in situ field estimates of N_r EFs to previous lab and field studies. For similar fuel types, we find ΣNH_x EFs are of the same magnitude or larger than lab‐based NH₃ EF estimates, and ΣNO_y EFs are smaller than lab NO_x EFs.

中文翻译：

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2018年夏季美国西部野火产生的反应性氮排放

烟羽中的反应性氮（N _r）在臭氧的产生，二次气溶胶的形成以及固定氮向生态系统的沉积中起着重要作用。西部野火云化学，气溶胶吸收和氮（WE‐CAN）野外实验于2018年夏季使用NSF / NCAR C-130研究飞机对全美国西部23种野火中的烟雾进行了采样。我们根据经验估计从估计排放量的80分钟内采样的火中归一化的N _r标准化过量混合比和排放因子，并探讨这些火之间N _r的主要形式的变异性。我们发现还原的N化合物占总测得活性氮的大部分（39％–80％；中位数= 66％）（ΣN _{- [R} ）的排放量。WE‐CAN期间采样的烟羽在排放后具有快速的化学转化特征。其结果是，在几分钟内发射总测量氧化的氮（后Σ NO _ÿ）和测量的总Σ NH _X（NH ₃  +  p NH ₄）具有修饰的燃烧效率（MCE）的更稳健相关比NO _X和NH ₃本身。ΣNH的比值_X /ΣNO _ý显示与MCE负相关，与先前的研究一致的。与总的测量的正关系ΣN _ř这表明燃烧条件和燃料氮含量/挥发差异都有助于观察到还原态和氧化态N _r的分布变化。此外，我们将N _r EF的现场评估结果与之前的实验室和现场研究进行了比较。出于同样的燃料类型，我们发现Σ NH _X EF文件是相同的数量级或比基于实验室的NH大₃ EF估计和Σ NO _ÿ的EF比实验室NO小_X的EF。