Analysis of aerosol optical depth in the UV range based on the data taken at Belsk, Poland by the Brewer Spectrophotometer Mark II and the sunphotometer Cimel CE 318

Aerosol optical depth (AOD) data in the range 1020 nm - 340 nm collected by the Cimel sunphotometer at Belsk, Poland in 2002 has been analysed together with the aerosol optical depth in the range 320 nm -306 nm inferred from the standard direct sun Brewer spectrophotometer measurements. Calibration of the Brewer has been performed in situ (by the Langley plot analysis) using the data from clear sky days. Results of the comparison of the simultaneous measurements of AOD in the UV-A (Cimel) and the UV-B (Brewer) are presented. These results, as well as the analysis of the variability of the Angstrom parameter calculated for the wavelength pairs situated in the UV range and its comparison with Angstrom parameter inferred from the visible range of wavelength shows that the extrapolation of aerosol optical properties from the visible to the UV-B range of wavelengths used e.g. in many radiation models can lead to the substantial errors in the simulated radiation intensity and should be treated with caution.