Why are older diesel cars so dirty in winter?
January 22, 2020
Euro 5 diesel cars have been found to emit many more times NOx emissions than expected from their legal limit value. These high rates get even higher at cooler temperatures. As remote sensing measurements show, essentially all manufactures decrease their emission controls when leave the window for the official test.
German Public TV documentary (in German): https://www.daserste.de/information/wirtschaft-boerse/plusminus/sendung/diesel-thermofenster-100.html