Black carbon, brown carbon, and selective smoke aerosol absorption during large-scale wildfires in Alaska in 2019 and Canada in 2023
G.I. Gorchakov1, A.V. Karpov1, R.A. Gushchin1, O.I. Datsenko1, E.G. Semoutnikova2
1A.M. Obukhov Institute of Atmospheric Physics Russian Academy of Sciences, Moscow, Russia
2Lomonosov Moscow State University, Moscow, Russia
Keywords: largescale smoke haze, smoke aerosol, optical characteristic, black carbon, brown carbon, selective absorption, imaginary part of index of refraction, spectral dependence, AERONET
Abstract
The smoky haze that occurs during massive forest fires radically transforms the radiation regime of the atmosphere over large areas, which is significantly influenced by the variability of the imaginary part of the refractive index of smoke aerosol. The variability of shortwave radiation fluxes in a smoke-laden atmosphere is driven by variations in the optical and microphysical properties of smoke aerosols, including the spectral dependencies of the imaginary part of the refractive index. These dependencies are determined by the presence of black carbon, brown carbon, and radiation-selective absorbing organic compounds in the aerosol particles. This study analyzes the aforementioned spectral dependencies using AERONET data during large-scale wildfires in Alaska in 2019 and Canada in 2023. The analysis includes cases of extreme radiation absorption by black and brown carbon, where the imaginary part of the refractive index at a wavelength of 440 nm reached 0.50 and 0.27, respectively. Variations in the spectral dependence of the imaginary part of the refractive index during moderate manifestations of selective absorption of smoke aerosol during massive fires in Alaska and Canada are analyzed. Approximations for the spectral dependence of the imaginary part of the refractive index are proposed. Estimates of aerosol radiative forcing at the top of the atmosphere are given for extreme manifestations of radiation absorption in the visible and near-infrared spectral regions by black carbon and brown carbon and during anomalous selective absorption. The results indicate a need in the detailed study of large-scale atmospheric smoke.
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