Aerosol effects on UV radiation in nonurban regions

The effect of variable tropospheric aerosol conditions on UV radiation is a nalyzed using both model simulations and UV radiation measurements. A sensi tivity study of the aerosol effect on UV radiation is performed by numerica l modeling with a focus on the dependence on wavelength, solar zenith angle , and detector geometry. Potential day to day variability in atmospheric ae rosols produces changes of spectral integrated radiation quantities of the order of 20% to 45%. Equivalent effects are induced by total ozone variatio ns between 40 Dobson units (DU) and 90 DU for those spectral integrals havi ng a high Sensitivity in the UV-B wavelength range. At least 80% of the aer osol effect is caused by typical variations in aerosol optical depth and si ngle scattering albedo. The variation of other aerosol optical properties s uch as phase function, spectral extinction, and extinction profile is of mi nor importance. Our results indicate that information on both aerosol optic al depth and single scattering albedo is necessary in most cases for an ade quate description of aerosol impact on W radiation. The sensitivity study s upplies a tool for the comparison of aerosol effects derived from various U V radiation measurements with respect to spectral weighting and/or detector geometry. The results of the sensitivity study contribute to the discussio n of a local aerosol study performed using measurements we made at Hoher Pe issenberg, Germany. Two years of ozone and nitrogen dioxide photolysis freq uency measurements are analyzed with respect to aerosol-induced radiation c hanges in the UV-B and W-A wavelength region. A procedure is introduced to extract the aerosol influence from the impact of other atmospheric paramete rs, particularly from the ozone amount for investigations in the UV-B. A co mparison of the derived aerosol effect with model simulations shows good ag reement.