INTERCOMPARISON CAMPAIGN OF VERTICAL OZONE PROFILES INCLUDING ELECTROCHEMICAL SONDES OF ECC AND BREWER-MAST TYPE-A GROUND-BASED UV-DIFFERENTIAL ABSORPTION LIDAR

An intercomparison campaign was conducted at the Observatoire de Haute Provence (OHP) in Southern France in September 1989 in order to compa re the three instruments used for vertical tropospheric ozone profilin g in the European TOR (Tropospheric Ozone Research Project) network: b alloon borne ECC and Brewer-Mast sondes and a ground based UV-DIAL (Di fferential Absorption Lidar). Additionally, a stratospheric lidar syst em and the Dobson spectrophotometer of the OHP were operated. Seven si multaneously measured vertical ozone profiles gave evidence for system atic differences of 15% between both types of electrochemical sondes i n the troposphere, the Brewer-Mast sondes reading the smaller ozone va lues. These differences might be explained on the one hand by a possib le contamination of the ozone sensor with reducing substances, causing a negative bias mainly for Brewer-Mast sondes and, on the other hand, by the evolution of the sonde background current during the flight, c ausing a positive bias for ECC sondes and a negative bias for Brewer-M ast sondes. The tropospheric lidar system, measuring the vertical ozon e distribution between 6 and 12-15 km, showed ozone concentrations int ermediate between the sonde results. This is in good agreement with it s estimated systematic error of better than 7% in the upper tropospher e. In the stratosphere, the differences between electrochemical sondes and the lidar are between 5 and 10% before the normalisation with the total ozone values measured by the Dobson spectrophotometer, and alwa ys below 5% after. While the Dobson normalisation thus corrects rather well the stratospheric part of the sonde profile, it only partially r educes errors occurring in the troposphere.