SPECTROSCOPIC MEASUREMENT OF FREE-RADICALS (OH, NO3) IN THE ATMOSPHERE

Due to their high chemical reactivity free radicals are the driving force for most chemical processes in the atmosphere, this is true, in particular, for OH- and NO3-radicals. Thus, knowledge of the concentration of those species in the atmosphere is a key requirement for the investigation of atmospheric chemistry. The low concentration of free radicals makes measurements particularly difficult, however. Among several techniques applied to the problem UV/visible differential absorption spectroscopy appears to be the most successful for the observation of OH and NO3. Detection limits of the order of 10(6) and 10(7) molec/cm3, respectively, have been reached, which are sufficiently low to resolve diurnal profiles of both species. The relative importance of both radicals in the NO(x) to nitric acid conversion is discussed.