Aerosol single scattering albedo retrieved from measurements of surface UV irradiance and a radiative transfer model

Aerosol single scattering albedo (omega), the ratio of aerosol scattering coefficient to total aerosol extinction coefficient, at UV wavelengths is an important aerosol radiative parameter in determining surface UV irradiance. Surface measurements of total and diffuse UV irradiance in the summer and fall of 1999 at the seven narrowband wavelength channels of an UV multifilter rotating shadowband radiometer (UVMFR-SR) at Black Mountain, N.C., were coupled with a tropospheric ultraviolet radiative transfer model to produce values of omega. Its value ranged from 0.65 to 0.91 at 300 nm, 0.71 to 0.96 at 305.5 nm, 0.73 to 0.97 at 311.4 nm, 0.74 to 0.91 at 317.6 nm, 0.76 to 0.96 at 325.4 nm, 0.77 to 0.97 at 332.4 nm, and 0.80 to 0.99 at 368 nm. Error in this procedure decreases with increasing aerosol optical depth (AOD), from +/-0.63 at AOD=0.05 to +/-0.04 at AOD=1.0 averaged over the seven wavelengths. The current values of omega have a slightly wider variation than values reported from a previous study at the same site. The lower values of omega could indicate that, over the site, preferential absorption of UV radiation by black carbon aerosols could be occurring. More values of omega in the UV spectrum will allow for better estimation of this parameter for UV radiative transfer modeling and will lessen error in estimation of surface UV irradiances.