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Ozone formation in 1990 and now

Things have changed since in the 1990s catalysts for vehicles were introduced. In order to understand these changes, you should imagine what happens with an air package that travels from the city towards the forest ...

Ozone formation in 1990 and now Please click to enlarge.

To put it simply, a high ratio of hydrocarbons to nitrogen oxides in the exhaust gas increases ozone production. In the 1990s, both the concentrations of nitric oxide and hydrocarbons in cities were very high - as did ozone production. When the air package moved towards the surrounding countryside, the pollutants were diluted; but they were sufficient for a consistently strong ozone production.

Today, thanks to the catalysts in the cities, hardly any hydrocarbons are emitted. Nitrogen oxide emissions have only slightly declined. The smaller ratio of hydrocarbons to nitrogen oxides leads to a significantly lower ozone production!
Naturally, nitrogen oxide emissions must also be reduced in the future since these are also harmful to the climate and health. However, with respect to ozone production, elevated nitrogen oxide concentrations are no longer problematic at the current hydrocarbon concentration level.

Excursus on Ozone Production

The ozone problem has not yet been solved worldwide. Our result of the reduced ozone production relates only to Germany. Although a similar trend is to be expected in Europe, there are also some countries with heavily obsolete or completely different vehicle fleets!

Nitrogen Oxides in German Inner Cities