The validation of vertical columns of ozone and NO2 from the SYMOCS instrument.

Abstract

UV-visible Differential Optical Absorption Spectroscopy (DOAS) has proved to be a useful method for measuring slant and vertical column amounts of several atmospheric trace gases. Two ground-based UV-visible spectrometers (SYMOCS-VIS and SYMOCS-UV) were developed at the Norwegian Institute for Air Research (NILU). This report describes the validation of the vertical columns of ozone and NO2 retrieved from the SYMOCS instruments. The study show that both ozone and NO2 columns measured with the SYMOCS instrument are in very good agreement with measurements performed with the NDSC qualified SAOZ instrument and the standard instrument from a intercomparison campaign. Interpretation with respect to the meteorological conditions and a comparison with results from a 3D chemical transport model have also been performed. The general agreement between modelled and observed O3 columns are good during winter/spring. However, the model underestimates total ozone by 30-50 DU during the autumn season. The seasonal and diurnal variation in NO2 is captured by the model, but the model severely underestimates the NO2 columns, mostly during fall, but also in the winter/spring period.