Relative importance of black carbon, brown carbon, and absorption enhancement from clear coatings in biomass burning emissions
Relative importance of black carbon, brown carbon, and absorption enhancement from clear coatings in biomass burning emissions
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DOI：
10.5194/acp-17-5063-2017
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发表时间：
2016-11
影响因子：
6.3
通讯作者：
R. Pokhrel;E. Beamesderfer;Nick L. Wagner;J. Langridge;D. Lack;T. Jayarathne;E. Stone;C. Stockwell-C.-S
中科院分区：
文献类型：
--
作者：
R. Pokhrel;E. Beamesderfer;Nick L. Wagner;J. Langridge;D. Lack;T. Jayarathne;E. Stone;C. Stockwell-C.-S
抽象的。米苏拉第四个消防实验室 (FLAME-4) 期间燃烧了多种具有全球重要意义的生物质燃料。多通道光声吸收光谱仪 (PAS) 测量 405、532 和 660 nm 处的干燥吸收度以及 405 和 660 nm 处的热剥蚀 (250 °C) 吸收度。吸收系数按照三种不同的方法分为黑碳 (BC)、棕碳 (BrC) 和透镜作用的贡献，一个极端是假设热剥离器有效去除有机物的方法，另一个极端是基于黑碳 (BC) 具有单位埃指数的假设的方法。所采用的方法提供了 BrC 对吸收的潜在重要性的范围，但平均而言，两种方法估计的 BrC 吸收分数的比率存在 2 倍的差异。 BrC 在较短可见波长下的吸收与 BC 的吸收同等或更重要，其最大贡献在 405 nm 处占气溶胶总吸收的 92%，在 532 nm 处占总吸收的 58%。据估计，透镜最多贡献总吸收的 30%，但通常贡献远小于此。吸收增强和估计的 BrC 吸收分数与排放气溶胶的元素碳与有机碳比率 (EC ∕ OC) 具有良好的相关性，而与改进的燃烧效率 (MCE) 的相关性较弱。先前的研究表明，随着黑色与有机气溶胶 (OA) 质量的比例增加，BrC 会变得更暗（更大的虚折射率）。这项研究与这些发现一致，但也表明 BrC 的总吸收分数呈现相反的趋势：随着气溶胶排放的有机分数的增加和 EC ∕ OC 比率的降低而增加。
Abstract. A wide range of globally significant biomass fuels were burned during the fourth Fire Lab at Missoula Experiment (FLAME-4). A multi-channel photoacoustic absorption spectrometer (PAS) measured dry absorption at 405, 532, and 660 nm and thermally denuded (250 °C) absorption at 405 and 660 nm. Absorption coefficients were broken into contributions from black carbon (BC), brown carbon (BrC), and lensing following three different methodologies, with one extreme being a method that assumes the thermal denuder effectively removes organics and the other extreme being a method based on the assumption that black carbon (BC) has an Angstrom exponent of unity. The methodologies employed provide ranges of potential importance of BrC to absorption but, on average, there was a difference of a factor of 2 in the ratio of the fraction of absorption attributable to BrC estimated by the two methods. BrC absorption at shorter visible wavelengths is of equal or greater importance to that of BC, with maximum contributions of up to 92 % of total aerosol absorption at 405 nm and up to 58 % of total absorption at 532 nm. Lensing is estimated to contribute a maximum of 30 % of total absorption, but typically contributes much less than this. Absorption enhancements and the estimated fraction of absorption from BrC show good correlation with the elemental-carbon-to-organic-carbon ratio (EC ∕ OC) of emitted aerosols and weaker correlation with the modified combustion efficiency (MCE). Previous studies have shown that BrC grows darker (larger imaginary refractive index) as the ratio of black to organic aerosol (OA) mass increases. This study is consistent with those findings but also demonstrates that the fraction of total absorption attributable to BrC shows the opposite trend: increasing as the organic fraction of aerosol emissions increases and the EC ∕ OC ratio decreases.