4. General conclusion and outlook

Although air quality continues to improve (reduction in NO ₂ and fine particle (PM) concentrations in major cities in particular), threshold exceedances are still observed for NOx, PM and O ₃ in France as well as in other European countries [BM 2 502] .

The road transport sector is the biggest contributor to urban NOx emissions and the second biggest contributor to PM emissions, after the residential/tertiary sector. Over the past 30 years, road transport emissions have been steadily...