Foreign manufacturers, including Ford of Europe, which is based in Cologne, drew sharp criticism Wednesday after they declined to participate in the €500 million fund to improve urban air quality. Ford said it would take other measures to reduce emissions, including incentives for people to trade in older cars.

Vehicles are Germany’s single most important export product and, in many parts of the world, the most visible symbol of German engineering prowess. Within the country, BMWs, Mercedes-Benzes and Porsches are a source of considerable pride and an essential part of the postwar national self-image.

Diesels are particularly important to German carmakers, and the technology has a long history here — Rudolf Diesel, a German, invented the diesel engine. Because of diesel’s superior fuel economy today, it is a popular option with buyers of the large luxury cars that are profit centers for the industry. Until recently, Diesels outsold gasoline cars in Europe, thanks in part to de facto subsidies.

But their sales have been plummeting amid growing awareness that diesel exhaust causes serious lung ailments, including asthma and cancer. In July, sales of diesels in Germany fell 13 percent compared with a year earlier, according to government figures published on Wednesday.

A further impediment to sales is that numerous cities around Europe, including BMW’s home of Munich, are considering bans on older diesel cars. The city governments of Madrid and Athens have already said they will ban diesels altogether in 2025. Britain and France have said they want to end sales of new diesel vehicles by 2040.



Last week, a lower court judge in Stuttgart ruled that a ban on diesels in the city center was the only way to address nitrogen oxide pollution that frequently exceeded levels considered acceptable. If affirmed on appeal, the decision could pave the way for widespread diesel bans.