Policies introduced across Europe to reduce the emission of nitrogen oxides (NOx) from road transport have been effective, despite an increase in vehicle fuel consumption between 1990 and 2005, according to a new study.

Man-made nitrogen oxides (NOx), including nitric oxide (NO) and nitrogen dioxide (NO2) emissions are air pollutants which affect climate change, human health and ecosystems. Europe contributed about 30 per cent of global NOx emissions in 1990, excluding emissions from burning biomass and from shipping. Policies introduced between 1990 and 2005 have been effective in reducing NOx emissions in Europe, in contrast to other regions, notably Asia, Africa, Latin America and the Middle East, where NOx emissions continue to rise. In 2005, road transport was responsible for 40 per cent of NOx emissions in Europe.

The study, partly conducted under the EU project CARBOSOL1, detailed trends in NOx emissions in Europe from the 1880s until 2005. Five periods representing distinct trends were identified. 1880-1950 saw moderate growth in the consumption of liquid fuel. During 1950- 1980, growth rates were dramatic.

Particular attention has been paid to the effect of policy regulations since 1990. Overall, NOx emissions increased by 13 per cent between 1980 and 1990 and peaked in 1990, despite a fall in emissions in Eastern Europe from worsening economic conditions.

In Western Europe, road transport emissions increased, even though consumption of transport fuel dropped in most countries following record high fuel prices.

It is argued that regulations from the 1970s to improve combustion in vehicles and reduce emissions of carbon monoxide and hydrocarbons unintentionally contributed to increased NOx emissions. During 1990-2000, emissions from the traffic sector fell across Europe by 23 per cent overall. Fuel consumption increased in Western Europe but new regulations and technologies reduced emissions. In Eastern Europe, fewer NOx polluting vehicles on the road contributed to reduced NOx emissions.

During 2000-2005, road transport emissions in Western Europe became decoupled from fuel consumption and continue to fall as a result of regulations. In contrast, emissions in Eastern Europe rose due to increased prosperity, largely due to increases in road transport. Differences in emission levels in Western and Eastern Europe were narrowing by 2005.

Both road transport emissions and total NOx emissions fell by about 30 per cent between 1990 and 2005 through regulations such as the Euro Standards for emissions from new vehicles2, the Gothenburg Protocol3, which sets emissions ceilings for four pollutants, including NOx by 2010, and the National Emission Ceilings (NEC) Directive4.

Compared with petrol vehicles fitted with advanced catalytic converters, even late technology diesel vehicles emit higher levels of NOx with a rising proportion of NO2 - a side-effect of oxidation catalysts in the exhaust system. The number of diesel vehicles increased rapidly between 1990-2005: if these new vehicles had been petrol-fuelled, NOx emissions would have fallen by a further 30 per cent.

Although overall NOx pollution is falling in Europe, the proportion of NO2 is increasing with increased diesel consumption. The researchers suggest that with the next generation of emission standards to limit NOx (and Particulate Matter) from road vehicles (Euro 5 in 2009-2012, and especially Euro 6 in 2014- 2016)2, NOx emissions will continue to fall for both petrol and diesel vehicles. However, we can expect time delays of up to eight years in some countries for the regulations to become fully effective as replacing older vehicles takes time.

CARBOSOL was supported by the European Commission under the Fifth Framework Programme. http://europa.eu/scadplus/leg/en/lvb/l28186.htm��