Observationally constrained representation of brown carbon emissions from wildfires in a chemical transport model
Observationally constrained representation of brown carbon emissions from wildfires in a chemical transport model
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化学传输模型中野火棕色碳排放的观测约束表示
DOI：
10.1039/d1ea00059d
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Saleh, Rawad
中科院分区：
文献类型：
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作者：
Neyestani, Soroush E.;Saleh, Rawad
2015年8月，美国西北部发生大规模野火，阿拉斯加和加拿大没有发生重大火灾。由于美国大部分碳质气溶胶（CA），包括黑碳（BC）和棕碳（BrC），主要来自西北野火的排放，本月提供了一个独特的机会来测试天气研究和预测中的野火BrC代表性化学模型（WRF-Chem）。我们进行了平行模拟，（1）不考虑BrC吸收，（2）考虑BrC吸收，（3）考虑BrC吸收以及由于光漂白引起的衰减。我们使用了一套全面的广泛和伪密集的光学特性，即气溶胶光学厚度（AOD），气溶胶吸收光学厚度（AAOD），吸收朗斯特伦指数（AAE）和单次散射散射（SSA），以限制模型输出对气溶胶机器人网络（AERONET）的观测。我们发现，占BrC吸收和光漂白导致最好的协议与观测气溶胶吸收（AAOD和AAE）。然而，与观测结果相比，该模型严重低估了AOD和SSA。我们将这种差异归因于模型中野火排放的二次有机气溶胶（SOA）形成所导致的散射缺失。为了验证这一假设，我们应用了野火SOA的零阶表示，这显着提高了AOD和SSA模型观察比较。我们的研究结果表明，BrC的吸收，其吸收的衰减，由于光漂白，以及SOA的形成应占在化学传输模型，以准确地代表CA排放野火。
The month of August 2015 featured extensive wildfires in the Northwestern U.S. and no significant fires in Alaska and Canada. With the majority of carbonaceous aerosols (CA), including black carbon (BC) and brown carbon (BrC), over the U.S. dominated by emissions from Northwestern wildfires, this month presented a unique opportunity for testing wildfire BrC representation in the Weather Research and Forecasting model with chemistry (WRF-Chem). We performed parallel simulations that (1) did not account for BrC absorption, (2) accounted for BrC absorption, and (3) accounted for BrC absorption as well as its decay due to photobleaching. We used a comprehensive set of extensive and pseudo-intensive optical properties, namely the aerosol optical depth (AOD), aerosol absorption optical depth (AAOD), absorption Ångström exponent (AAE), and single scattering albedo (SSA) to constrain the model output against observations from the Aerosol Robotic Network (AERONET). We found that accounting for BrC absorption and photobleaching resulted in the best agreement with observations in terms of aerosol absorption (AAOD and AAE). However, the model severely underestimated AOD and SSA compared to observations. We attributed this discrepancy to missing scattering due to missing secondary organic aerosol (SOA) formation from wildfire emissions in the model. To test this hypothesis, we applied a zeroth-order representation of wildfire SOA, which significantly improved the AOD and SSA model-observation comparison. Our findings indicate that BrC absorption, the decay of its absorption due to photobleaching, as well as SOA formation should be accounted for in chemical transport models in order to accurately represent CA emissions from wildfires.