MEASUREMENTS OF CHEMICALLY AND BIOLOGICALLY EFFECTIVE RADIATION REACHING THE GROUND

Solar ultraviolet radiation at the surface has been measured at Potsda m on cloudless days by spectrometer OL 752/10. The measurements are co mpared with broad-band filter measurements and with model calculations using a modified version of Green's model, which is independent of th e measurements. Input data to the model such as atmospheric ozone and aerosol optical thicknesses were measured by a Dobson and Brewer spect rophotometer as well as a Linke Feussner pyrheliometer, respectively. Differences between the model and the measurements are discussed in te rms of uncertainties in the calibration and errors of instruments as w ell as uncertainties in the model calculations including the errors of input data. It is demonstrated that different chemically and biologic ally effective radiances can be determined from only one set of measur ed spectral irradiance components, i.e. global radiation and diffuse d ownward and upward directed radiation. Examples of diurnal variations of the photochemical production of ozone and hydroxyl radicals as dete rmined from spectral irradiance measurements and measured concentratio ns of relevant trace gases are given. It is shown from the measured ir radiance that relations between different effects of radiation to the biosphere depend on solar zenith angle, and to a certain extent also o n atmospheric ozone. This has to be taken into account when adverse ef fects of changing UV radiation are evaluated. Radiation Amplification Factors derived from measurements correspond to those determined from model calculations.