[Air pollution in Switzerland--sources and extent]

The immediate source of air pollution is the fuel consumption that goes on in domestic heating (about 50%), in motor vehicles (about 25%), and in industry (about 25%). Immissions in towns and agglomerations do not only depend on the number and size of these issuing sources but also on the location and meteorological conditions. The average sulphur dioxide content in various towns amounts to 0.03-0.06 ppm in winter and in summer to 0.01-0.03 ppm. In weather conditions with little exchangeability, as is often the case in Zurich, particulate matter and sulphur dioxide concentrations frequently lie above threshold limits applied abroad. In the area of heavy traffic for instance, daily averages of carbon monoxide of up to 20 ppm, and maximum hourly averages of up to 50 ppm are measured--concentrations which lie also considerably above threshold limits. For nitrogen oxides, hydrocarbons and lead too, concentrations such as are measured in large foreign cities occur. In the future, coordinated time measurements will have to be carried out more frequently in Switzerland--especially in places with strong emitting sources and unfavorable meteorological conditions.