As far as I know, the NOX problems that were masked by the VW software cheating are not the kind of problems that everybody driving behind the car in question can smell.<p>As somebody who has driven only Peugeots for 14 years now, I can attest that the exhaust system of any Peugeot at any point in time is primarily occupied with rusting. I have to change some part of the exhaust every odd year. Most likely the smelly French cars you observed also have problems with rusted through exhausts.<p>Also: As somebody plagued with respiratory problems, I feel your pain. My health massively improved when I moved from the city back to my home town in the German woods.