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Brown carbon: A significant atmospheric absorber of solar radiation

机译：褐碳：一种重要的大气吸收太阳辐射

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摘要

Several recent observational studies have shown organic carbon aerosols to be a significant source of absorption of solar radiation. The absorbing part of organic aerosols is referred to as brown" carbon (BrC). Using a global chemical transport model and a radiative transfer model, we estimate for the first time the enhanced absorption of solar radiation due to BrC in a global model. The simulated wavelength dependence of aerosol absorption, as measured by the absorption ?ngstr?m exponent (AAE), increases from 0.9 for non-absorbing organic carbon to 1.2 (1.0) for strongly (moderately) absorbing BrC. The calculated AAE for the strongly absorbing BrC agrees with AERONET spectral observations at 440-870 nm over most regions but overpredicts for the biomass burning-dominated South America and southern Africa, in which the inclusion of moderately absorbing BrC has better agreement. The resulting aerosol absorption optical depth increases by 18% (3%) at 550 nm and 56% (38%) at 380 nm for strongly (moderately) absorbing BrC. The global simulations suggest that the strongly absorbing BrC contributes up to +0.25 W m-2 or 19% of the absorption by anthropogenic aerosols, while 72% is attributed to black carbon, and 9% is due to sulfate and non-absorbing organic aerosols coated on black carbon. Like black carbon, the absorption of BrC (moderately to strongly) inserts a warming effect at the top of the atmosphere (TOA) (0.04 to 0.11 W m-2), while the effect at the surface is a reduction (-0.06 to -0.14 W m-2). Inclusion of the strongly absorption of BrC in our model causes the direct radiative forcing (global mean) of organic carbon aerosols at the TOA to change from cooling (-0.08 W m-2) to warming (+0.025 W m-2). Over source regions and above clouds, the absorption of BrC is higher and thus can play an important role in photochemistry and the hydrologic cycle.
机译：最近的几项观测研究表明，有机碳气溶胶是吸收太阳辐射的重要来源。有机气溶胶的吸收部分称为棕色碳（BrC）。使用全局化学传输模型和辐射转移模型，我们首次估算了整体模型中BrC引起的太阳辐射吸收增强。通过吸收指数（AAE）测得的气溶胶吸收的模拟波长依赖性，从非吸收性有机碳的0.9增加到强（中度吸收）BrC的1.2（1.0）。 BrC与大多数地区在440-870 nm处的AERONET光谱观察结果一致，但对以生物质燃烧为主的南美和南部非洲地区的预测过高，其中吸收中等吸收的BrC具有更好的一致性，所产生的气溶胶吸收光学深度增加了18％ 550 nm（3％）和380 nm（380％）的56％（38％）对于强（中度）吸收BrC。全局模拟表明，强吸收BrC贡献高达+0.25 W m-2或19％其中，有72％归因于黑碳，而9％归因于硫酸盐和涂在黑碳上的非吸收性有机气溶胶。像黑碳一样，BrC的吸收（中等至强烈）会在大气层顶部（TOA）（0.04至0.11 W m-2）插入变暖效应，而在表面的吸收则降低（-0.06至- 0.14 W m-2）。在我们的模型中包括对BrC的强吸收，会导致TOA上有机碳气溶胶的直接辐射强迫（全局平均值）从冷却（-0.08 W m-2）变为加热（+0.025 W m-2）。在源区和云层之上，BrC的吸收较高，因此可以在光化学和水文循环中发挥重要作用。

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