EFFECT OF AEROSOLS ON SOLAR UV IRRADIANCES DURING THE PHOTOCHEMICAL ACTIVITY AND SOLAR ULTRAVIOLET-RADIATION CAMPAIGN

Surface UV irradiances were measured at two different sites in Greece during June 1996 under noncloudy conditions. The measured UV irradianc e are simulated by a radiative transfer model using measured ozone den sity and aerosol optical depth profiles. The absolute difference betwe en model and measurements ranges between -5% and +5% with little depen dence on wavelength. The temporal and solar zenith angle dependence in the difference between model and measurement suggests that part of th is difference may be explained by assumptions made about the aerosol s ingle-scattering albedo and phase function. Simulated spectra includin g aerosols are compared with calculated spectra excluding aerosols. It is found that for otherwise similar atmospheric conditions the UVB ir radiance is reduced with respect to aerosol free,conditions by 5% to 3 5% depending on the aerosol optical depth and single-scattering albedo . For the campaign period, changes in the aerosol loading gave larger variations in the surface UV irradiances than the changes seen in the ozone column.