The Impact of Smoke on the Ultraviolet and Visible Radiative Forcing Under Different Fire Regimes

Abstract

The quantification of the UV characteristics of smoke aerosols is valuable to UV Index forecasting, air quality studies, air chemistry studies, and assessments of the impacts on regional and global environmental changes. The wavelength dependence of the light absorption by smoke aerosol has been researched throughout the UV and visible spectral region and varies with fire type and aerosol composition. An objective of this study is to investigate the spectral optical properties (eg, extinction coefficient, single-scattering albedo, and asymmetry parameter), UV actinic fluxes, and radiative forcing of smoke of different fire regimes. The smoke aerosol information (eg, simulated smoke fields from biomass burning emission and vertical distribution of the mass concentration of smoke components) from WRF-Chem is used to distinguish 2 smoke types: flaming and smoldering. To compute the spectral optical properties for the fire regimes, the representative size distribution and spectral refractive index have been implemented into the Mie code, and the optical properties are used to run the tropospheric ultraviolet and visible radiative transfer model. We make comparisons between simulated model and measured actinic flux in the UV and visible spectra under smoke aerosol laden conditions. The WRF-Chem-SMOKE model simulates the smoke plume matched with fire locations and comparable aerosol optical depth (AOD) with satellite measurements. However, the correlation between the simulated and observed AOD is small, which implies that adjusting the fire size for the emission inputs and improving meteorological fields are required for further research. The smoke at selected locations reduces the UV actinic flux and increases the visible actinic flux above the plume at small solar zenith angles. The specific spectral response is dependent on the smoke type. Overall, the results of this investigation show that this approach is valuable to estimate the impact of smoke on UV and visible radiative fluxes