Analysis of ground based operational network data acquired during the September 1992 tract campaign

Abstract During the TRACT measuring campaign in September 1992 a great number of measurements were performed by more than 40 international working groups. In addition, also data from approx. 300 stations—included in operational networks—were collected and put into a database. A first overall review of these data of ground based operational networks is presented and a number of phenomena and results are explained, (a) the typical variation of ozone and nitrogen oxide concentrations with, on the one hand, a clear maximum of ozone in the afternoon and very low values in the night, measured by stations located at low and medium altitudes, and, on the other hand, weak diurnal variations at mountain sites; (b) the jump in ozone concentrations during the night of the 1st SOP due to passage of a cold front; (c) low temperatures resulting in low ozone concentrations in the southern Rhine valley on the second day of the 2nd SOP in foggy areas, which are typical of that region; (d) the exchange of polluted air masses between cities because of a rather complex flow over orographic terrain depending on the geostrophic wind direction. Many more aspects have been investigated; the data are now available.