A report by the European Environment Agency shows that road transport remains the single main source of nitrogen oxides (NOx), carbon monoxide (CO) and non-methane volatile organic compounds (NMVOCs), and the second-most important source of fine particulate emissions (PM10 and PM2.5) in the EU-27. The EEA's website gives more indications on the evolution of polluting substances due to road transports and its impact on human health and the ecosysten by saying:

' Between 1990 and 2006, nitrogen oxides (NOx) emissions decreased by 35 %, although the change of total NOx emissions between 2005 and 2006 was small, with a decrease of just 1.8 %, due to reductions that occurred in Germany, Italy and the United Kingdom. Nitrogen oxides are one of the main contributors to the formation of ground-level ozone, high levels of which can trigger severe respiratory problems. It also makes an important contribution to acidification and eutrophication. Electricity and heat production (e.g. at power stations) constitutes the main source of sulphur oxides (SOx) emissions (58.4 %), followed by manufacturing industries and construction sources (14.3 %). SOx is an acidifying pollutant which can also aggravate respiratory diseases. In contrast, agricultural activities are responsible for the vast majority of ammonia (NH3) emissions in EU-27. NH3 is an important pollutant which causes acidification and eutrophication. Livestock manure, together with emissions from the application of fertilisers account for more than 90 % of the NH3 generation. '

The EEA's report is available here

Source: EEA's webpage 'Transport remains main source of health-damaging pollutants'