Dilution and Photooxidation Driven Processes Explain the Evolution of Organic Aerosol in Wildfire Plumes
Dilution and Photooxidation Driven Processes Explain the Evolution of Organic Aerosol in Wildfire Plumes
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稀释和光氧化驱动的过程解释了野火羽流中有机气溶胶的演变
DOI：
10.1039/d1ea00082a
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Jen, Coty N
中科院分区：
文献类型：
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作者：
Akherati, Ali;He, Yicong;Garofalo, Lauren A;Hodshire, Anna L;Farmer, Delphine;Kreidenweis, Sonia M;Permar, Wade;Hu, Lu;Fischer, Emily V;Jen, Coty N
野火是区域和全球范围内一次有机气溶胶（POA）和二次有机气溶胶（SOA）的重要大气来源。然而，有很大的不确定性，周围的排放和物理化学过程，控制的转化，演变，和属性的POA和SOA在大型野火羽流。我们开发了一个动力学模型的羽流版本来模拟野火烟雾中有机气溶胶（OA）的稀释，氧化化学，热力学性质和微观物理。该模型被应用于研究在2018年夏天在美国西部的一次基于飞机的实地行动中截获的四个大型野火烟羽中的羽流OA。基于飞机第一次拦截羽流之前的稀释和氧化剂浓度的估计，我们模拟了从非常接近火灾到顺风几个小时的OA演变。我们的模型结果和敏感性模拟表明，稀释驱动的蒸发POA和SOA的同时光化学生产可能解释所观察到的OA质量随物理年龄的演变。然而，与测量值相比，该模型大大低估了OA的氧碳比的变化。此外，我们发现，在发射后的第一个小时内的快速化学转化是由高于环境的OH浓度（3 × 106-107分子/cm 3）驱动的，而在接下来的几个小时内的缓慢演变是由于低于环境的OH浓度（<106分子/cm 3）和耗尽的SOA前体。模型预测表明，在火灾顺风几个小时测得的OA仍以POA为主，但SOA分数在总OA的30%至56%之间变化。发现半挥发性、杂环和含氧芳族化合物以该顺序对SOA形成有实质性贡献（>90%）。未来的工作需要集中在更好地了解接近火灾的动态演变，并解决OA氧化态随物理年龄的快速变化。
Wildfires are an important atmospheric source of primary organic aerosol (POA) and precursors for secondary organic aerosol (SOA) at regional and global scales. However, there are large uncertainties surrounding the emissions and physicochemical processes that control the transformation, evolution, and properties of POA and SOA in large wildfire plumes. We develop a plume version of a kinetic model to simulate the dilution, oxidation chemistry, thermodynamic properties, and microphysics of organic aerosol (OA) in wildfire smoke. The model is applied to study the in-plume OA in four large wildfire smoke plumes intercepted during an aircraft-based field campaign in summer 2018 in the western United States. Based on estimates of dilution and oxidant concentrations before the aircraft first intercepted the plumes, we simulate the OA evolution from very close to the fire to several hours downwind. Our model results and sensitivity simulations suggest that dilution-driven evaporation of POA and simultaneous photochemical production of SOA are likely to explain the observed evolution in OA mass with physical age. The model, however, substantially underestimates the change in the oxygen-to-carbon ratio of the OA compared to measurements. In addition, we show that the rapid chemical transformation within the first hour after emission is driven by higher-than-ambient OH concentrations (3 × 106–107 molecules per cm3) and the slower evolution over the next several hours is a result of lower-than-ambient OH concentrations (<106 molecules per cm3) and depleted SOA precursors. Model predictions indicate that the OA measured several hours downwind of the fire is still dominated by POA but with an SOA fraction that varies between 30% and 56% of the total OA. Semivolatile, heterocyclic, and oxygenated aromatic compounds, in that order, were found to contribute substantially (>90%) to SOA formation. Future work needs to focus on better understanding the dynamic evolution closer to the fire and resolving the rapid change in the oxidation state of OA with physical age.