BAFU Ozone Summer 2003

• Hot and dry conditions in summer 2003 led to ozone levels that substantially exceeded the Swiss ambient air quality standard. We investigated how emissions and ozone levels would have changed in this period if the maximum speed limit on Swiss motorways were decreased from 120 to 80 km h-1. The model results suggested that nitrogen oxides (NOx) emissions from road traffic would decrease by about 4% and volatile organic compounds (VOC) emissions would not change significantly due to speed reduction.

• The effect of reduced speed limit on peak ozone levels would be less than 1%.

• We conclude from these results that temporary measures enforced in restricted regions are not sufficiently effective if the potential of emission reduction is less than 50%. More important for the ozone reductions in Switzerland are the long-term emission developments in Switzerland, in the adjacent countries and, to some extent, in the whole northern hemisphere.

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