The City of Lyon's 17 metering points comprise 42 sensors providing 61 different measurements. All information collected is automatically transferred to a computerised central data bank. This optical apparatus uses two laser beams to check air quality at distances from 500 metres to 2 kilometres. SO2 Produced mainly by coal and fuel oil, this gas is characteristic of urban areas and industrial zones. O3 Ozone plays a useful role in the upper atmosphere, but is an irritant at ground level, where its presence in the atmosphere is due to complex chemical reactions generated by NOx, hydrocarbons and sunlight.
Levels rise markedly in good weather.
CO This gas is produced by incomplete fuel combustion. The present rise in very fine dusts is due to increased use of diesel vehicles. Over the last 35 years a marked decrease in sulphur pollution has been observed in Lyon and its environs. There has been no significant change in the level of these gases. Measures taken by vehicle manufacturers to improve their engines have been counterbalanced by the constant increase in traffic.