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Some time this summer, the EC is expected to propose revisions to its Clean Air for Europe programme, an initiative linked to the National Emissions Ceilings (NEC) directive of 2001. Don’t fall asleep – this will affect anyone working in powertrain.

The NEC directive set binding emissions ceilings to be attained by each member state by 2010. It covered sulphur dioxide (SO2), nitrogen oxides (NOx), volatile organic compounds (VOCs) and ammonia.

Air quality is improving in Europe. NOx emissions have reduced dramatically. Between 1990 and 2004 they fell by about half in Germany. But the directive’s aim for most European countries in 2010 will not be met, which means additional measures will have to be taken.

The EC will expect improvements from all areas of industry, not just vehicle exhaust emissions. But the transport sector will have to play its part.

Some of the credit for the NOx reductions so far must go to the three-way catalysts for gasoline-engine vehicles and NOx storage catalysts for gasoline direct-injection cars. But the increasing number of diesels on the road makes it difficult to reduce this further. Experts say diesel engines actually account for an increase and there has been little decrease from the truck sector.

“Despite progress, pollution is still harming pubic health,” says environment commissioner Stavros Dimas. “The commission will focus on post-2012 policies and will adopt measures on vehicle emissions.”

The 2010 targets were just the first step toward longer-term objectives of getting pollution down to levels that cannot have an impact on our health. To achieve its targets for 2020, SO2 emissions will need to decrease by 82 per cent, NOx emissions by 60 per cent, VOCs by 51 per cent, ammonia by 27 per cent and particulate matter by 59 per cent relative to emissions in 2000.

That’s easier said than done. Tackling one pollutant can have unwanted effects on others. Adblue urea injection systems create ammonia to cut vehicles’ NOx emissions, but, as a result, they emit more ammonia.

The EC is likely to single out NOx as the issue to tackle with most vigour, introducing more defined legislation to encourage its reduction. Ground level ozone and particulate matter are the pollutants of most concern to health experts. They’re pretty bad for the lungs and life expectancy. Ozone is the result of a reaction between VOCs and NOx in the presence of sunlight.

Udo Lambrecht of the Institute for Energy and Environmental Research in Heidelberg has been involved in the research around the NEC and the clean air programme. He’s been closely observing the political scene too. “We’re starting to see national ceilings on greenhouse gases and we’ll see similar ceilings for NOx,” he says. “Emissions standards will be one of the tools to ensure that air quality standards are complied with.”

NOx is either NO or NO2. NOx may have decreased, says Lambrecht, but the decrease is mainly from reductions in NO.

Unexpectedly, in some areas with heavy traffic, NO2 concentrations have remained the same or are increasing. It is not exactly clear why this should be. It could be that there has been an increase in ozone in towns. Ozone (O3) chemistry is complex, but NO from exhausts could be reacting with O3 to form NO2. Or a straightforward increase in NO2 from exhaust gases could be responsible. Emissions regulations deal with NOx, not NO2 afterall.

All diesels have oxidation catalysts. They convert hydrocarbons and carbon monoxide into CO2 and water, but they also further oxidise NO into NO2. Diesel particle filters use some of the NO2 for regeneration, but it’s occasional and not all cars use them. Some do have continuous regeneration, but still won’t use all the NO2.

Cars with the next level of aftertreatment, deNOx catalysts, adsorb the NO2 and NO. The gases are treated and become N2 and H2O by using hydrogen in the exhaust gas stream. Some NO2 will escape and some will be released during regeneration as well.

Euro IV came into effect at the start of 2005 and mandates that NOx emissions can be no greater than 0.25g/km. It may have an effect on NO2 levels, but it depends on the technology used in individual models.

“First measurements show a very small reduction in NO2,” says Lambrecht. “There will be a reduction in NO by 2010, but higher levels of ozone chemistry mean reductions of NO2 are much lower.”

Until 2010, when EuroV will start to have an impact, not much can be expected. EuroV NOx levels are no greater than 0.18g/km; particulate matter is the focus.

“We’ll need further measures to comply with national emission ceilings for NO2 in Europe,” says Lambrecht. “In Germany, diesel trucks with lower emissions will be introduced earlier and we’ll also need further reductions from cars.” NOx treatment in diesels will be the main focus of EuroVI, although specific targets have not been set. Neither is there an EC proposal for trucks yet.

And the NEC directive will force national policy makers to consider other measures to improve air quality. That could mean environmental legislation, but there is much talk in Brussels of using more taxation. As with EuroIV, there could be tax concessions for the early introduction of anti-NOx technologies in cars and HGVs.

But if you were thinking that legislation was only going to squeeze powertrain engineers on CO2, you’re mistaken. NOx from vehicles is going to be a continuing and increasingly complex issue for the next decade.

• Udo Lambrecht was speaking at this year’s Vienna Motor Symposium.