Brown and black carbon in Beijing aerosol: Implications for the effects of brown coating on light absorption by black carbon
Brown and black carbon in Beijing aerosol: Implications for the effects of brown coating on light absorption by black carbon
复制标题
北京气溶胶中的棕碳和黑碳：棕色涂层对黑碳光吸收影响的影响
DOI：
10.1016/j.scitotenv.2017.05.061
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发表时间：
2017-12-01
影响因子：
9.8
通讯作者：
Dong, Shu-ping
中科院分区：
文献类型：
--
作者：
Cheng, Yuan;He, Ke-bin;Dong, Shu-ping
褐碳（BrC）作为一类新兴的颗粒有机化合物，越来越多地被纳入气候模型中，可以有效吸收特定波长的太阳辐射。水溶性有机碳 (WSOC) 通常用作 BrC 的替代品；然而，它仅占总有机碳 (OC) 质量的有限部分，在城市大气中可能低至约 20%。使用甲醇作为萃取溶剂，分离出北京气溶胶中约 90% 的 OC，并测量了紫外至可见波长范围内的吸收光谱。与甲醇可溶性 OC (MSOC) 相比，WSOC 在 365 nm 处低估了 BrC 吸收约 50%。将北京气溶胶中测量的 BrC 质量吸收效率转换为 BrC 的虚折射率，随后用于计算 BrC 涂层引起的黑炭光吸收增强 (E-abs)。相对于纯散射涂层引起的 E-abs，在 BrC 涂层的情况下，归因于透镜效应的 E-abs 有所降低。然而，这种减少被 BrC 壳吸收的影响所掩盖，表明 BrC 涂层的总体效果是 E-abs 的增加。甲醇萃取显着减少了热光分析过程中 OC 的炭化，导致测量的元素碳 (EC) 质量大幅增加，并且不同热光方法的 EC 测量的一致性明显改善。 (C) 2017 Elsevier B.V. 保留所有权利。
Brown carbon (BrC) is increasingly included in climate models as an emerging category of particulate organic compounds that can absorb solar radiation efficiently at specific wavelengths. Water-soluble organic carbon (WSOC) has been commonly used as a surrogate for BrC; however, it only represents a limited fraction of total organic carbon (OC) mass, which could be as low as about 20% in urban atmosphere. Using methanol as the extraction solvent, up to approximately 90% of the OC in Beijing aerosol was isolated and measured for absorption spectra over the ultraviolet-to-visible wavelength range. Compared to methanol-soluble OC (MSOC), WSOC underestimated BrC absorption by about 50% at 365 nm. The mass absorption efficiencies measured for BrC in Beijing aerosol were converted to the imaginary refractive indices of BrC and subsequently used to compute BrC coating-induced enhancement of light absorption (E-abs) by black carbon. E-abs attributed to lensing was reduced in the case of BrC coating relative to that caused by purely-scattering coating. However, this reduction was overwhelmed by the effect of BrC shell absorption, indicating that the overall effect of BrC coating was an increase in E-abs. Methanol extraction significantly reduced charring of OC during thermal-optical analysis, leading to a large increase in the measured elemental carbon (EC) mass and an apparent improvement in the consistency of EC measurements by different thermal-optical methods. (C) 2017 Elsevier B.V. All rights reserved.