Measurements of chemically and biologically effective radiation reaching the ground

Solar ultraviolet radiation at the surface has been measured at Potsdam on cloudless days by spectrometer OL 752/10. The measurements are compared with broad-band filter measurements and with model calculations using a modified version of Green's model, which is independent of the measurements. Input data to the model such as atmospheric ozone and aerosol optical thicknesses were measured by a Dobson and Brewer spectrophotometer as well as a Linke Feussner pyrheliometer, respectively. Differences between the model and the measurements are discussed in terms of uncertainties in the calibration and errors of instruments as well as uncertainties in the model calculations including the errors of input data. It is demonstrated that different chemically and biologically effective radiances can be determined from only one set of measured spectral irradiance components, i.e. global radiation and diffuse downward and upward directed radiation. Examples of diurnal variations of the photochemical production of ozone and hydroxyl radicals as determined from spectral irradiance measurements and measured concentrations of relevant trace gases are given.It is shown from the measured irradiance that relations between different effects of radiation to the biosphere depend on solar zenith angle, and to a certain extent also on atmospheric ozone. This has to be taken into account when adverse effects of changing UV radiation are evaluated. Radiation Amplification Factors derived from measurements correspond to those determined from model calculations.