From Measurements to Models: Toward Accurate Representation of Brown Carbon in Climate Calculations
From Measurements to Models: Toward Accurate Representation of Brown Carbon in Climate Calculations
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DOI：
10.1007/s40726-020-00139-3
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发表时间：
2020-03
影响因子：
7.3
通讯作者：
R. Saleh
中科院分区：
文献类型：
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作者：
R. Saleh
审查目的气候模型研究预测的棕碳 (BrC) 吸收的直接辐射效应具有高度不确定性，其值范围在 +0.03 W/m2 和 +0.57 W/m2 之间。本综述致力于找出这种不确定性的来源，这些挑战源自将测量结果转化为模型输入的挑战，并从导致模型中 BrC 表征得到改进的最新进展中汲取经验教训。 最新发现 以前认为 BrC 仅吸收短可见光和紫外光，但最近发现 BrC 包含在中长可见波长中具有强吸收性的成分，其光吸收效率接近炭黑。生物质和生物燃料燃烧作为大气 BrC 主要来源的经典观点仍然成立，最近的测量表明 BrC 光学特性和燃烧条件之间存在很强的相关性。目前模型中尚未考虑到 BrC 的其他燃烧源，包括低效燃煤和使用重燃油的船舶发动机。大气中的气相、水相和颗粒相反应会产生次级 BrC 并使初级 BrC 漂白/变暗。气候模型研究表明，预测的 BrC 辐射效应对假设的光学特性和大气老化机制很敏感。总结 BrC 可分为四个光学类别，每个光学类别在中可见光吸收方面相差一个数量级。这些类别大致映射到 BrC 源，其中次生 BrC 的吸收性最低，来自高温燃烧的 BrC 吸收性最强。有证据表明，每个类别都表现出特有的理化性质（分子大小、挥发性和溶解度），可以利用这些特性来设计测量方法，量化 BrC 跨类别的分布以及每个类别的光漂白/变暗率。利用该框架开发 BrC 参数化有望增强其在气候模型中的代表性。
Purpose of ReviewThe direct radiative effect of brown carbon (BrC) absorption predicated by climate-modeling studies is highly uncertain, with values ranging between +0.03 W/m2and + 0.57 W/m2. This review strives to identify sources of this uncertainty stemming from challenges in translating measurements into model inputs and to draw lessons from recent advances that lead to improved BrC representation in models.Recent FindingsPreviously thought to absorb only short-visible and UV light, BrC was recently shown to comprise components that are strongly absorptive in the mid- and long-visible wavelengths, with light-absorption efficiencies approaching that of black carbon. The classic picture of biomass and biofuel combustion being the major sources of atmospheric BrC still holds, with recent measurements indicating a strong correlation between BrC optical properties and combustion conditions. Other combustion sources of BrC, currently not accounted for in models, include low-efficiency coal combustion and ship engines utilizing heavy fuel oil. Gas-phase, aqueous, and particle-phase reactions in the atmosphere produce secondary BrC and bleach/darken the primary BrC. Climate-modeling studies revealed that predicted BrC radiative effects are sensitive to the assumed optical properties and atmospheric aging mechanisms.SummaryBrC can be grouped into four optical classes, each separated by an order of magnitude in mid-visible light absorption. The classes are approximately mapped to BrC sources, with secondary BrC being the least absorbing and BrC from high-temperature combustion the most absorbing. There is evidence that each class exhibits characteristic physicochemical properties (molecular size, volatility, and solubility), which can be leveraged to design measurements that quantify distributions of BrC across classes as well as rates of photobleaching/darkening for each class. Utilizing this framework to develop BrC parameterizations promises to enhance its representation in climate models.