Constraining emissions of volatile organic compounds from western US wildfires with WE-CAN and FIREX-AQ airborne observations
Constraining emissions of volatile organic compounds from western US wildfires with WE-CAN and FIREX-AQ airborne observations
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DOI：
10.5194/acp-23-5969-2023
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发表时间：
2023-05
影响因子：
6.3
通讯作者：
Lixu Jin;W. Permar;Vanessa Selimovic;Damien Ketcherside;R. Yokelson;R. Hornbrook;E. Apel;I. Ku;Jeffrey L. Collett Jr.;A. Sullivan;D. Jaffe;J. Pierce;A. Fried;M. Coggon;G. Gkatzelis;C. Warneke;E. Fischer;Lu Hu
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作者：
Lixu Jin;W. Permar;Vanessa Selimovic;Damien Ketcherside;R. Yokelson;R. Hornbrook;E. Apel;I. Ku;Jeffrey L. Collett Jr.;A. Sullivan;D. Jaffe;J. Pierce;A. Fried;M. Coggon;G. Gkatzelis;C. Warneke;E. Fischer;Lu Hu
抽象的。生物质燃烧(BB)对大气中挥发性有机化合物(VOCs)负荷的影响是高度不确定的。在这里，我们应用GEOS-化学输送模式(CTM)在∼25公里分辨率下限制美国西部的BB排放。在CTMS中广泛使用的三个BB排放清单中，库存-库存比较表明，美国西部14个模拟的BB VOC排放总量彼此吻合在30%-40%之间。然而，由于三个清单的区域平均排放比率(ERs，反映了为特定生物群和植被分类分配的ERs)，单个VOCs的排放量可能相差1-5倍。我们进一步使用在WE-CAN(西部野火云化学、气溶胶吸收和氮实验)和FIREX-AQ(火灾对区域对全球环境和空气质量的影响)实地活动中进行的飞机观测来评估GEOS-Chem模拟。尽管受到不同的全球BB库存或应用不同的注入高度假设的驱动，模型-观测比较表明，GEOS-Chem模拟对观测到的垂直剖面的预测不足3-7倍。该模型显示，在低/无烟雾条件下，大多数物种的偏差很小或没有偏差。因此，我们将负面模型偏差主要归因于低估了这些库存中的BB排放量。模型中三倍的BB排放再现了观测到的主要化合物的垂直分布，即CO、丙烷、苯和甲苯。然而，对于含氧的VOCs，特别是甲醛、甲酸、醋酸和集中的≥C3醛，该模型没有显示出显著的改善，这表明该模型在受BB影响的环境中缺少这些化合物的二次来源。库存中对主要BB排放量的低估可能是由于低估了燃烧的有效干物质数量，而不是受飞机和地面测量的限制，火灾探测、喷射高度或ERS的误差。我们不能排除嵌套的GEOS-Chem中潜在的次网格不确定性(即无法完全解析火羽)，这可以部分解释负的模型偏差，尽管使用较长期地面测量的粗略计算和评估有助于支持干物质燃烧被低估的论点。在GEOS-Chem实施的14个BB挥发性有机化合物的总ER仅占测量的161个挥发性有机化合物总数的一半(∼为75 ppb，−为150ppm 1)。这揭示了广泛使用的BB排放清单中大量缺失的活性有机碳。考虑到有效干物质燃烧(×3)和未建模VOCs(×2)的不确定性，我们推断，在这两个火灾季节，BB对美国西部这两个火季VOC初级排放通量的贡献分别为10%和45%，而标准GEOS-Chem只有1%-10%。
Abstract. The impact of biomass burning (BB) on the atmospheric burden of volatile organic compounds (VOCs) is highly uncertain. Here we apply the GEOS-Chem chemical transport model (CTM) to constrain BB emissions in the western USA at ∼ 25 km resolution. Across three BB emission inventories widely used in CTMs, the inventory–inventory comparison suggests that the totals of 14 modeled BB VOC emissions in the western USA agree with each other within 30 %–40 %. However, emissions for individual VOCs can differ by a factor of 1–5, driven by the regionally averaged emission ratios (ERs, reflecting both assigned ERs for specific biome and vegetation classifications) across the three inventories. We further evaluate GEOS-Chem simulations with aircraft observations made during WE-CAN (Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption and Nitrogen) and FIREX-AQ (Fire Influence on Regional to Global Environments and Air Quality) field campaigns. Despite being driven by different global BB inventories or applying various injection height assumptions, the model–observation comparison suggests that GEOS-Chem simulations underpredict observed vertical profiles by a factor of 3–7. The model shows small to no bias for most species in low-/no-smoke conditions. We thus attribute the negative model biases mostly to underestimated BB emissions in these inventories. Tripling BB emissions in the model reproduces observed vertical profiles for primary compounds, i.e., CO, propane, benzene, and toluene. However, it shows no to less significant improvements for oxygenated VOCs, particularly for formaldehyde, formic acid, acetic acid, and lumped ≥ C3 aldehydes, suggesting the model is missing secondary sources of these compounds in BB-impacted environments. The underestimation of primary BB emissions in inventories is likely attributable to underpredicted amounts of effective dry matter burned, rather than errors in fire detection, injection height, or ERs, as constrained by aircraft and ground measurements. We cannot rule out potential sub-grid uncertainties (i.e., not being able to fully resolve fire plumes) in the nested GEOS-Chem which could explain the negative model bias partially, though back-of-the-envelope calculation and evaluation using longer-term ground measurements help support the argument of the dry matter burned underestimation. The total ERs of the 14 BB VOCs implemented in GEOS-Chem only account for half of the total 161 measured VOCs (∼ 75 versus 150 ppb ppm−1). This reveals a significant amount of missing reactive organic carbon in widely used BB emission inventories. Considering both uncertainties in effective dry matter burned (× 3) and unmodeled VOCs (× 2), we infer that BB contributed to 10 % in 2019 and 45 % in 2018 (240 and 2040 Gg C) of the total VOC primary emission flux in the western USA during these two fire seasons, compared to only 1 %–10 % in the standard GEOS-Chem.