Spatial correlations of daily and weekly maximum day exposure of solar UV radiation in the continental United States

Abstract

Impacts of UV radiation on humans, plants and animals involve both acute exposures to high levels of UV radiation and chronic exposures to moderate to high levels of UV radiation. However exposure estimates are often limited by the relatively low density of ground-based measurements of solar ultraviolet irradiance. This study relates the spacing of measurements to the accuracy of estimating daily exposure (chronic exposure) and maximum daily exposure over a 7-day interval (acute exposure) to solar UV. 300 nm, 368 nm, and UVB broadband measurements using multi-filter rotating shadow band radiometers and a broadband radiometer were paired by day for locations within a climate region. The variability in exposures in the various wavebands was evaluated using spatial statistics and interpolations made using kriging methods. The spatial correlation of the 300 nm and UVB acute exposures were greater than the correlation for the chronic daily exposures for distances up to 500 km. Conversely, the spatial correlation of the 368 nm acute exposure was greater than that for the chronic daily exposures for distances up to 500 km. A decrease in the variability in the acute over chronic exposure resulted in an improved ability to estimate the acute exposure across the full 1100 km domain. Limitations to the interpolation of 368 nm acute exposure were assumed to be due to local cloud effects on the radiation. Improvements in the ability to interpolate chronic 300 nm, 368 nm, and UVB exposures from the present USDA UVB Climate Network will require longer exposure periods.