Black Carbon and Brown Carbon and Selective Smoke Aerosol Absorption during Massive Wildfires in Alaska in 2019 and Canada in 2023

Abstract

Smoky haze which occurs during large-scale wildfires essentially transforms the radiative regime of the atmosphere over large territories. 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 dependences of the imaginary part of the refractive index. These dependences are determined by the presence of black carbon, brown carbon, and radiation-selective absorbing organic compounds in aerosol particles. This study analyzes the aforementioned spectral dependences based on AERONET data during large-scale wildfires in Alaska in 2019 and Canada in 2023. The analysis includes the cases of extreme radiation absorption by black and brown carbon, where the imaginary part of the refractive index at a wavelength of 440 nm attained 0.50 and 0.27, respectively. Variations in the spectral dependence of the imaginary part of the refractive index under 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 suggested. The aerosol radiative forcing at the top of the atmosphere is estimated for the cases of extreme radiation absorption by black carbon and brown carbon in the visible and near-infrared spectral regions and of anomalous selective absorption. The results can be useful in monitoring of the radiative regime of the atmosphere and for the development of atmospheric remote sounding techniques.