Nighttime and daytime dark oxidation chemistry in wildfire plumes: an observation and model analysis of FIREX-AQ aircraft data
Nighttime and daytime dark oxidation chemistry in wildfire plumes: an observation and model analysis of FIREX-AQ aircraft data
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DOI：
10.5194/acp-21-16293-2021
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发表时间：
2021-11-08
影响因子：
6.3
通讯作者：
Brown, Steven S.
中科院分区：
文献类型：
--
作者：
Decker, Zachary C. J.;Robinson, Michael A.;Brown, Steven S.
整个美国西部的野火规模越来越大，导致人类暴露在烟雾中的数量增加，并对健康造成了相关的负面影响。生物质燃烧(BB)烟雾(包括野火)对区域空气质量的影响取决于排放、运输和化学，包括排放的BB挥发性有机化合物(BB-VOCs)被羟基自由基(OH)、硝酸根(NO3)和臭氧(O-3)氧化。白天，当光线穿透羽流时，BBVOCs主要被O-3和OH氧化。相比之下，在夜间或在光学密度较高的羽状物中，BBVOCs主要由O-3和NO3氧化。这项工作侧重于白天和夜间氧化之间的过渡，这对二次污染物的形成和氮氧化物(NOx=NO+NO2)的损失具有重要意义，但一直没有得到充分的研究。我们介绍了在FIREX-AQ(火灾对区域环境和空气质量的影响)期间观察到的野火羽流，FIREX-AQ是一项涉及多个飞机、地面、卫星和移动平台的实地行动，于2019年夏天在美国举行，旨在研究野火和农业燃烧排放和大气化学。我们使用两架研究飞机--NASA DC-8和NOAA Twin Otter的观测数据，以及详细的化学盒模型，包括最新的酚类机理，来分析中午、日落和夜间采集的烟雾样本。飞机观测表明，中午和天黑后羽流中N3的产生率都在0.1-1.5ppbv/h(-1)范围内。模拟的初始瞬时反应性分别为80.1%、87.7%和99.6%。在森林或城市环境中，NO3的初始反应性是典型值的10-10(4)倍，与BBVOCs的反应占太阳光羽流中NO3损失的97%(JNO(2)至4+/-10(-3)S(-1))，而传统的光化学与NO反应和光解是NO3损失的次要途径。烯烃和呋喃主要被OH和O-3氧化(烯烃11%-43%，54%-88%；呋喃分别为18%-55%，39%-76%)，但酚类氧化分为NO3，O-3和OH(分别为26%-52%，22%-43%，16%-33%)。在落日羽流和光学厚度较厚的羽流中，硝酸根氧化占酚类化学损失的26%-52%。硝基邻苯二酚的产率在33%到45%之间变化，在当天晚些时候排放的BB羽流中的NO3化学负责72%-92%(在光学厚度为中午的羽流中为84%)的硝基邻苯二酚的形成，并控制总体上的硝基酚的形成。结果是，到第二天日出时，过夜的硝基酚生成途径占到NOx损失的56%+/-2%。在我们模拟的所有夜间烟羽中，日出时存在剩余的NOx(13%-57%)和BBVOCs(8%-72%)。
Wildfires are increasing in size across the western US, leading to increases in human smoke exposure and associated negative health impacts. The impact of biomass burning (BB) smoke, including wildfires, on regional air quality depends on emissions, transport, and chemistry, including oxidation of emitted BB volatile organic compounds (BB-VOCs) by the hydroxyl radical (OH), nitrate radical (NO3), and ozone (O-3). During the daytime, when light penetrates the plumes, BBVOCs are oxidized mainly by O-3 and OH. In contrast, at night or in optically dense plumes, BBVOCs are oxidized mainly by O-3 and NO3. This work focuses on the transition between daytime and nighttime oxidation, which has significant implications for the formation of secondary pollutants and loss of nitrogen oxides (NOx = NO + NO2) and has been understudied. We present wildfire plume observations made during FIREX-AQ (Fire Influence on Regional to Global Environments and Air Quality), a field campaign involving multiple aircraft, ground, satellite, and mobile platforms that took place in the United States in the summer of 2019 to study both wildfire and agricultural burning emissions and atmospheric chemistry. We use observations from two research aircraft, the NASA DC-8 and the NOAA Twin Otter, with a detailed chemical box model, including updated phenolic mechanisms, to analyze smoke sampled during midday, sunset, and nighttime. Aircraft observations suggest a range of NO3 production rates (0.1-1.5 ppbv h(-1)) in plumes transported during both midday and after dark. Modeled initial instantaneous reactivity toward BBVOCs for NO3, OH, and O-3 is 80.1 %, 87.7 %, and 99.6 %, respectively. Initial NO3 reactivity is 10-10(4) times greater than typical values in forested or urban environments, and reactions with BBVOCs account for > 97% of NO3 loss in sunlit plumes (jNO(2) up to 4 +/- 10(-3) s(-1)), while conventional photochemical NO3 loss through reaction with NO and photolysis are minor pathways. Alkenes and furans are mostly oxidized by OH and O-3 (11 %-43 %, 54 %-88% for alkenes; 18 %-55 %, 39 %-76 %, for furans, respectively), but phenolic oxidation is split between NO3, O-3, and OH (26 %-52 %, 22%-43 %, 16 %-33 %, respectively). Nitrate radical oxidation accounts for 26 %-52% of phenolic chemical loss in sunset plumes and in an optically thick plume. Nitrocatechol yields varied between 33% and 45 %, and NO3 chemistry in BB plumes emitted late in the day is responsible for 72 %-92% (84% in an optically thick midday plume) of nitrocatechol formation and controls nitrophenolic formation overall. As a result, overnight nitrophenolic formation pathways account for 56% +/- 2% of NOx loss by sunrise the following day. In all but one overnight plume we modeled, there was remaining NOx (13 %-57 %) and BBVOCs (8 %-72 %) at sunrise.