Direct Measurements and Implications of the Aerosol Asymmetry Parameter in Wildfire Smoke During FIREX-AQ

IF 3.8 2区 地球科学 Q2 METEOROLOGY & ATMOSPHERIC SCIENCES
A. T. Ahern, C. A. Brock, M. Lyu, K. Slovacek, R. H. Moore, D. M. Murphy
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Abstract

We present direct measurements of the asymmetry parameter (g) from biomass burning aerosol at two wavelengths using the Laser Imaging Nephelometer. We compare the measurements with Mie theory calculations based on optically measured size distributions and with g values derived from hemispheric backscatter (b) measurements using both an integrating and an imaging nephelometer. During the FIREX-AQ field mission, we measured the optical and microphysical properties of smoke plumes that had been emitted between 0.5 and 8.5 hr earlier. We find that the measured g can only be reproduced from particle size distribution measurements using a higher refractive index than is typically retrieved from remote measurements and assumed in some models. Retrievals performed using the GRASP algorithm suggest the refractive index is wavelength-dependent with n = 1.55 ± 0.03 at λ = 660 nm and (1.63 ± 0.04) at λ = 405 nm. Using a simple radiative transfer equation, we show that the instantaneous aerosol cooling of the planet by fresh smoke is increased by 20% when evaluated using the measured g values instead of assuming n = 1.52. Besides improving model representations of radiative cooling by fresh smoke, using a more accurate aerosol optical model can improve retrievals of aerosol microphysical properties from remote sensing techniques. Better retrievals will provide a more accurate constraint on the emissions inventories used in global and regional models. This will ultimately reduce the uncertainty in radiative forcing associated with the increasing frequency and magnitude of wildfires.

Abstract Image

野火烟雾中气溶胶不对称参数在FIREX-AQ期间的直接测量及其意义
我们使用激光成像浊度计在两个波长下直接测量生物质燃烧气溶胶的不对称参数(g)。我们将测量结果与基于光学测量尺寸分布的Mie理论计算结果以及使用积分和成像浊度计的半球后向散射(b)测量结果得出的g值进行了比较。在FIREX-AQ野外任务期间,我们测量了0.5至8.5小时前排放的烟羽的光学和微物理特性。我们发现,测量的g只能通过使用比通常从远程测量和某些模型中假设的更高折射率的粒度分布测量来再现。利用GRASP算法进行的检索表明,折射率与波长有关,在λ = 660 nm处n = 1.55±0.03,在λ = 405 nm处n = 1.63±0.04。使用一个简单的辐射传递方程,我们表明,当使用测量的g值而不是假设n = 1.52进行评估时,新鲜烟雾对地球的瞬时气溶胶冷却增加了20%。除了改进新烟辐射冷却的模型表示外,使用更精确的气溶胶光学模型可以改进遥感技术对气溶胶微物理特性的检索。更好的检索将为全球和区域模式中使用的排放清单提供更准确的约束。这将最终减少与野火频率和强度增加有关的辐射强迫的不确定性。
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来源期刊
Journal of Geophysical Research: Atmospheres
Journal of Geophysical Research: Atmospheres Earth and Planetary Sciences-Geophysics
CiteScore
7.30
自引率
11.40%
发文量
684
期刊介绍: JGR: Atmospheres publishes articles that advance and improve understanding of atmospheric properties and processes, including the interaction of the atmosphere with other components of the Earth system.
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