On the dynamics of photochemical smog over the Swiss MiddlelandAresults of the first POLLUMET field experiment

The Swiss Middleland is a 300 x 50 km large plain embedded between the Jura, whose highest elevations are between 1000 and 2000 m MSL, and the Alps, whose highest peaks are about 4000 m MSL. Because this plain is the main residence area of Switzerland with a great variety of emission sources, it is also a location with high photosmog concentrations during the summer months. Within the framework of the Swiss POLLUMET (Air Pollution and Meteorology) programme, an initial summer smog field experiment was carried out during July 1990 with the participation of different research groups from Switzerland and Germany. The measurements showed that the ozone concentrations within the atmospheric boundary layer were remarkably variable. The highest concentrations in the upper mixed layer varied between 100 and 130 ppb. The background ozone concentration in the upper atmospheric boundary layer increased from day to day. However, a clear indication of long-range transport could not be found. Remarkable local and regional concentration differences are not only based on the complex structure of the large emission sources (highways, urban plumes). They are also the result of the interaction of convectively driven motion systems like slope and valley winds and mountain-plain circulation.