The nitrogen budget of laboratory-simulated western US wildfires during the FIREX 2016 Fire Lab study Atmospheric Chemistry and Physics

Reactive nitrogen (Nr, defined as all nitrogen-containing compounds except for N2 and N2O) is one of the most important classes of compounds emitted from wildfire, as Nr impacts both atmospheric oxidation processes and particle formation chemistry. In addition, several Nr compounds can contribute to health impacts from wildfires. Understanding the impacts of wildfire on the atmosphere requires a thorough description of Nr emissions. Total reactive nitrogen was measured by catalytic conversion to NO and detection by NO–O3 chemiluminescence together with individual Nr species during a series of laboratory fires of fuels characteristic of western US wildfires, conducted as part of the FIREX Fire Lab 2016 study. Data from 75 stack fires were analyzed to examine the systematics of nitrogen emissions. The measured Nr ∕ total-carbon ratios averaged 0.37 % for fuels characteristic of western North America, and these gas-phase emissions were compared with fuel and residue N∕C ratios and mass to estimate that a mean (±SD) of 0.68 (±0.14) of fuel nitrogen was emitted as N2 and N2O. The Nr detected as speciated individual compounds included the following: nitric oxide (NO), nitrogen dioxide (NO2), nitrous acid (HONO), isocyanic acid (HNCO), hydrogen cyanide (HCN), ammonia (NH3), and 44 nitrogen-containing volatile organic compounds (NVOCs). The sum of these measured individual Nr compounds averaged 84.8 (±9.8) % relative to the total Nr, and much of the 15.2 % “unaccounted” Nr is expected to be particle-bound species, not included in this analysis. Grant no. NA16OAR4310100

反应性氮（Reactive nitrogen, Nr，定义为除氮气（N₂）与一氧化二氮（N₂O）外的所有含氮化合物）是野火排放的核心化合物类别之一，因其既会干预大气氧化过程，也会影响颗粒物形成的化学机制。同时多种Nr化合物还会加重野火引发的健康危害。要全面解析野火对大气系统的影响，需对Nr排放特征开展系统性表征。作为FIREX Fire Lab 2016研究的组成部分，研究团队针对美国西部野火典型燃料开展系列实验室燃烧试验，采用催化转化-NO-O₃化学发光法测定总反应性氮（Total reactive nitrogen），同时对单体Nr物种进行定性定量分析。本研究对75次烟道燃烧试验的数据集进行分析，以厘清氮排放的系统规律。针对北美西部典型燃料，实测Nr/总碳（Total-carbon, TC）比值的平均值为0.37%；结合燃料与残余物的N/C比值及质量守恒关系，估算得到燃料氮中平均（±标准差）0.68（±0.14）以N₂与N₂O形式排放。本次检出的单体Nr化合物包括：一氧化氮（NO）、二氧化氮（NO₂）、亚硝酸（HONO）、异氰酸（HNCO）、氰化氢（HCN）、氨（NH₃）以及44种含氮挥发性有机化合物（NVOCs, nitrogen-containing volatile organic compounds）。上述实测单体Nr化合物的总占比相对于总Nr的平均值为84.8%（±9.8%），剩余约15.2%的“未核算”Nr主要为颗粒结合态物种，未纳入本次分析范围。资助编号：NA16OAR4310100