The German Environment Agency (UBA) said on Saturday it was doubtful about the environmental benefits of introducing incentives for drivers of older diesel vehicles to trade them in for newer models. Chancellor Angela Merkel is due to hold a high-level meeting on Sunday to discuss whether to require the car industry to carry out costly hardware upgrades for older diesel vehicles to reduce inner-city pollution, government sources said on Friday.
Transport Minister Andreas Scheuer, a member of Merkel's Bavarian CSU allies, favours incentives to exchange older vehicles for newer ones to reduce overall pollution caused by the fleet of cars on the road and to avoid driving bans.
But Frankfurter Allgemeine newspaper cited an internal paper from UBA as saying that in the best case scenario, such an exchange premium would only reduce nitrogen oxide pollution by 0.7 micrograms per cubic meter.
That would be a very small amount compared with the overall pollution, which is at between 73 and 78 micrograms in cities like Stuttgart or Munich, the newspaper cited UBA as saying.
A spokesman for UBA, which is Germany's main environmental protection agency, confirmed that the newspaper report was accurate.
It would be better to make retrofits mandatory, he said, meaning carmakers would build in so-called selective catalytic reduction (SCR) systems. He added that this was the only way to avoid driving bans.
Older diesel vehicles such as those of the Euro-4 standard sometimes have lower emissions than the more modern Euro-6 standard diesel vehicles.
Scheuer has not ruled out the possibility of a retrofit with catalysts, which is favoured by the Environment Ministry - run by the Social Democrats - but he considers that solution to be more complicated technically and more expensive.
Merkel has tasked Scheuer with finding a solution to make older diesel cars cleaner and to avoid large-scale bans on diesel cars.
The car industry has lobbied against equipping old diesel models with extra emissions control technology because that could cost billions of euros.