Comparative analysis of erythemal and cataractogenic solar UV irradiance under varying atmospheric and geometrical conditions: implications for UV index interpretation

<title>Abstract</title> <p>The biological effects of solar UV radiation depend on both its spectral distribution and the wavelength-dependent response of the biological system. Each effect is quantified by biologically effective UV irradiance through wavelength weighting of the solar UV spectrum by the corresponding biological action spectrum. The UV Index is derived from erythemally effective UV irradiance and is widely used to communicate the potential hazard of solar UV radiation to human skin. Its applicability to ocular exposure, however, remains uncertain. This study investigates the influence of geometrical and atmospheric conditions on erythemally and cataractogenically effective solar UV irradiances. The analysis is based on rigorous spectral simulations performed under realistic geometrical configurations and atmospheric conditions. The analysis focuses on receiving surface orientation, ozone, aerosol loading, aerosol type, and ground reflectance. The results indicate that erythemally and cataractogenically effective UV irradiances respond similarly to variations in ozone and receiving surface orientation but differently to changes in aerosol optical properties and ground albedo. Notably, changes in aerosol type and ground albedo may induce opposite trends in the two irradiances. These findings have significant implications for UV Index interpretation, indicating that it may not always adequately reflect the ocular hazard associated with solar UV radiation.</p>