Car manufacturers have expressed disquiet over plans in Germany to upgrade exhaust emissions filtering systems on older diesel cars as a way to avoid vehicle bans in some major cities.
A number of German cities, including Bonn, Stuttgart, Cologne and Hamburg, have announced bans on older, more heavily polluting diesel vehicles in a bid to cut emissions of particulates and nitrogen oxides.
The German transport ministry has now released a 30-page document setting out guidelines for getting regulatory approval to install upgraded exhaust filtering systems on older cars.
"Now it is the turn of the retrofit industry to develop effective systems to meet all limits and regulations," transport minister Andreas Scheuer said in a statement.
The Federal Motor Transport Authority would grant approval quickly so that the retrofit systems could be offered on the market as soon as possible, he said.
However, the German manufacturers’ trade association, the VDA, wants customers to buy new cars with cleaner engines, rather than trying to clean up older vehicles.
"We cannot give a guarantee for a vehicle in which third-party exhaust purification systems have been retrofitted," VDA president Bernhard Mattes told Die Welt newspaper.
"If a customer has his vehicle modified, then he and the retrofitter are responsible for any consequential damage."
According to a report in Automotive News Europe, manufacturers are divided over who will pay the retrofit costs, given that most older diesel cars met clean air rules at the time when they were sold.
Volkswagen and Daimler said they would cover some retrofit costs, while BMW refused, proposing instead incentives to trade in old vehicles for new ones.
Volkswagen also said that customers may not benefit from installing new exhaust systems on older cars. "All concepts known to us to date have disadvantages for our customers, such as increased fuel consumption and thus increased CO2 emissions and, in some cases, reduced performance," VW research and development head Frank Welsch said in a statement.
BMW said exhaust system upgrades that would not penalize fuel consumption or cause additional wear and tear could take up to three years to develop and certify.
Selling newer cars through incentives combined with an increase in sales of electric cars and the relevant charging infrastructure would bring down pollution levels in inner cities much faster than trying to retrofit older vehicles, BMW said.
German environmental lobby groups ClientEarth and Deutsche Umwelthilfe (DUH) won a landmark ruling in Leipzig in February last year which said that German cities would be allowed to ban older diesel vehicles from zones worst affected by pollution.
Since then several cities have announced bans on older vehicles which do not conform to the latest Euro 6d engine emissions standards. Hamburg has banned older diesel cars from the city center, and other cities, including Berlin and Stuttgart, the home of Germany's car industry, are set to introduce similar bans.
Of the 15 million diesel cars on Germany's roads, only 2.7 million have Euro-6 technology. Some estimates of the cost of upgrading the exhaust cleaning of just the Euro-5 fleet run into tens of billions of Euros.
German manufacturers have already agreed to spend up to €3,000 per vehicle to upgrade engine management software to make exhaust filtering systems more effective, but environmentalists say these measures are insufficient.
The move to outlaw noxious diesel emissions has spread around the world. Paris, Madrid, Mexico City and Athens have said they plan to ban diesel vehicles from city centres by 2025, while Copenhagen wants to ban new diesel cars from entering the city as soon as next year. France and the UK plan to ban new gasoline and diesel cars by 2040.
However, the latest diesel cars will be unaffected by the ban as the latest technology means they meet emissions standards, but many new car buyers are already moving away from the technology in favour of hybrids and EVs.
However, while diesels produce high levels of nitrogen oxide, they emit relatively low levels of carbon dioxide, a greenhouse gas. So moves to control one environmental problem may end up undermining efforts to combat another.
Already the UK has seen levels of CO2 from car exhausts increase for the first time in 20 years because of the switch away from diesel and back to petrol engines.