Biomass burning (BB) produces large quantities of carbonaceous aerosol (black carbon and organic aerosol, BC and OA, respectively), which significantly degrade air quality and impact climate. BC absorbs radiation, warming the atmosphere, while OA typically scatters radiation, leading to cooling. However, some OA, termed brown carbon (BrC), also absorbs visible and near UV radiation; although, its properties are not well constrained. We explore three aircraft campaigns from important BB regions with different dominant fuel and fire types (Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen [WE-CAN] in the western United States and ObseRvations of Aerosols above CLouds and their intEractionS and Cloud-Aerosol-Radiation Interactions and Forcing for Year downwind of southern Africa) and compare them with simulations from the global chemical transport model, GEOS-Chem using GFED4s. The model generally captures the observed vertical profiles of carbonaceous BB aerosol concentrations; however, we find that BB BC emissions are underestimated in southern Africa. Our comparisons suggest that BC and/or BrC absorption is substantially higher downwind of Africa than in the western United States and, while the Saleh et al. (2014, https://doi.org/10.1038/ngeo2220) and FIREX parameterizations based on the BC:OA ratio improve model-observation agreement in some regions, they do not sufficiently differentiate absorption characteristics at short wavelengths. We find that photochemical whitening substantially decreases the burden and direct radiative effect of BrC (annual mean of +0.29 W m⁻² without whitening and +0.08 W m⁻² with). Our comparisons suggest that whitening is required to explain WE-CAN observations; however, the importance of whitening for African fires cannot be confirmed. Qualitative comparisons with the OMI UV aerosol index suggest our standard BrC whitening scheme may be too fast over Africa.

中文翻译：

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调查美国西部 (WE-CAN) 和南部非洲 (ORACLES 和 CLARIFY) 火灾中的碳质气溶胶及其吸收特性

生物质燃烧 (BB) 会产生大量含碳气溶胶（分别为黑碳和有机气溶胶，BC 和 OA），这会显着降低空气质量并影响气候。BC 吸收辐射，使大气变暖，而 OA 通常散射辐射，导致冷却。然而，一些被称为褐碳 (BrC) 的 OA 也会吸收可见光和近紫外线辐射；虽然，它的属性并没有受到很好的约束。我们探索了来自重要 BB 地区的三个具有不同主要燃料和火灾类型的飞机战役（西部野火云化学实验、气溶胶吸收、和美国西部的氮 [WE-CAN] 以及对云层上方气溶胶及其相互作用和云-气溶胶-辐射相互作用和南部非洲下风年强迫的观测，并将它们与全球化学输运模型 GEOS 的模拟结果进行比较- 化学使用 GFED4s。该模型通常捕捉观察到的含碳 BB 气溶胶浓度的垂直剖面；然而，我们发现南部非洲的 BB BC 排放量被低估了。我们的比较表明，非洲下风向的 BC 和/或 BrC 吸收量远高于美国西部，而 Saleh 等人。(2014, https://doi.org/10.1038/ngeo2220) 和基于 BC:OA 比率的 FIREX 参数化提高了某些地区的模型观测一致性，它们不能充分区分短波长的吸收特性。我们发现光化学增白显着降低了 BrC 的负担和直接辐射效应（年平均值为 +0.29 W m^-2没有增白和 +0.08 W m ^-2有）。我们的比较表明需要白化来解释 WE-CAN 观察结果；然而，美白对非洲火灾的重要性无法得到证实。与 OMI 紫外线气溶胶指数的定性比较表明，我们的标准 BrC 美白方案在非洲可能太快了。