The direct influence of aerosols on UV irradiance and the development of a synthetic current UV index.

摘要

The extinction of solar radiation by atmospheric aerosols influences the Ultraviolet (UV) flux at the surface, which in turn has implications on both human and environmental health. In this study we present measurements of aerosol optical depth (taua) in the UV at Boulder, Colorado and Atlanta, Georgia using direct measurements of solar UV radiation. The wavelength dependence of taua and the single scattering albedo (oo) are determined from the measured values of tau a. Daily averages of taua range between 0.09 and 0.52 at Boulder and between 0.23 and 2.09 for Atlanta between the wavelengths of 332 and 340 nm. The average Angstrom exponent (alpha) is 0.83 at Boulder and 1.43 in Atlanta. Results clearly show that aerosols have a significant effect on the UV Index. Day-to-day changes in the UV index during the one month measurement period in Atlanta range between 2-3 UV Index units at solar noon. It is estimated that when changes in taua and o o occur simultaneously, the UV Index can change up to 6 units from one day to the next at solar noon in the Atlanta area. The single scattering albedo (oo) was estimated to range between 0.8 and 0.99 for Atlanta. The results suggest an increasing trend in oo with increases in taua. In addition, A new synthetic current UV Index is calculated which expands to nearly 10,000 cities the number of current UV Index reports that can be distributed to the public in the United States. Right now, current UV Index values are limited to specific UV measuring sites, constrained by the difficulties of maintaining accurate calibration within the network of UV instruments. The distribution of UV Index values to more cities will increase the public's awareness of the harmful effects of the sun.