气候变化领域集成服务门户(CCPortal): Absorption closure in highly aged biomass burning smoke

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DOI	10.5194/acp-20-11201-2020
	Absorption closure in highly aged biomass burning smoke
	Taylor J.W.; Wu H.; Szpek K.; Bower K.; Crawford I.; Flynn M.J.; Williams P.I.; Dorsey J.; Langridge J.M.; Cotterell M.I.; Fox C.; Davies N.W.; Haywood J.M.; Coe H.
发表日期	2020
ISSN	1680-7316
起始页码	11201
结束页码	11221
卷号	20 期号:19
英文摘要	The optical properties of black carbon (BC) are a major source of uncertainty in regional and global climate studies. In the past, detailed investigation of BC absorption has been hampered by systematic biases in the measurement instrumentation. We present airborne measurements of aerosol absorption and black carbon microphysical properties in highly aged biomass burning plumes measured 4-8 d from their source over the southeast Atlantic Ocean during CLARIFY-2017, using a suite of novel photoacoustic spectrometers to measure aerosol absorption at 405, 514, and 655 nm and a single-particle soot photometer to measure the BC mass concentration, size, and mixing state. These measurements are of sufficient quality and detail to provide constraint on optical schemes used in climate models for the first time in biomass burning plumes far from their source-an aerosol environment that is one of the most important climatically. The average absorption Ångström exponents (AAE) were 1.38 over the wavelength range from 405 to 514 nm and 0.88 over the range from 514 to 655 nm, suggesting that brown carbon (BrC) contributed to 11±2 % of absorption at 405 nm. The effective organic aerosol (OA) mass absorption coefficient (MAC) was 0:31±0:09 m2 g-1 at 405 nm. The BC particles were universally thickly coated, and almost no externally mixed BC particles were detected. The average MAC of BC was 20 ± 4, 15 ± 3, and 12 ± 2 m2g-1 at wavelengths of 405, 514, and 655 nm respectively, with equivalent absorption enhancements of around 1:85 ± 0:45 at all three wavelengths, suggesting that the thick coatings acted as a lens that enhanced light absorption by the BC. We compared the measured MAC and AAE values with those calculated using several optical models and absorption parameterisations that took the measured BC mass and mixing state as inputs. Homogeneous grey-sphere Mie models were only able to replicate MAC for some low (real and imaginary) values of the complex BC refractive index (mBC) at the shortest wavelength, but they would have to use unrealistically low values of mBC to accurately replicate the AAE. A core-shell Mie model was able to generate good agreement for MAC in the green-red end of the visible spectrum for most values of mBC. However, there are no possible values of mBC that produce MAC values that agree with our observations at all three wavelengths, due to a wavelengthdependent underestimation of the MAC of the underlying BC core. Four semiempirical parameterisations from the literature were also tested, linking the BC mixing state to either the MAC or absorption enhancement. Two of these schemes produced results that agreed within a few percent with the measured MAC at all three wavelengths, and the AAE agreed well when discounting the effects of BrC. Our results uniquely demonstrate the validity of absorption parameterisations, as well as the failings of Mie calculations, in this highly aged environment. We recommend that future work should conduct similar analyses in environments where BC has different properties; future studies should also investigate the impact of implementing these types of schemes within climate models as well as the impact of developing equivalent schemes for light scattering by soot particles at visible wavelengths. © 2020 Author(s).
语种	英语
scopus关键词	aerosol property; biomass burning; black carbon; climate modeling; optical property; photometer; smoke; Atlantic Ocean; Atlantic Ocean (Southeast)
来源期刊	ATMOSPHERIC CHEMISTRY AND PHYSICS
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/247501
作者单位	Centre for Atmospheric Science, Department of Earth and Environmental Sciences, University of Manchester, Manchester, United Kingdom; National Centre for Atmospheric Science, University of Manchester, Manchester, United Kingdom; Met Office, Exeter, United Kingdom; College for Engineering Mathematics and Physical Sciences, University of Exeter, Exeter, United Kingdom; School of Chemistry, University of Bristol, Bristol, United Kingdom
推荐引用方式 GB/T 7714	Taylor J.W.,Wu H.,Szpek K.,et al. Absorption closure in highly aged biomass burning smoke[J],2020,20(19).
APA	Taylor J.W..,Wu H..,Szpek K..,Bower K..,Crawford I..,...&Coe H..(2020).Absorption closure in highly aged biomass burning smoke.ATMOSPHERIC CHEMISTRY AND PHYSICS,20(19).
MLA	Taylor J.W.,et al."Absorption closure in highly aged biomass burning smoke".ATMOSPHERIC CHEMISTRY AND PHYSICS 20.19(2020).