> Euro standards are backwards; they have stricter CO2 emissions regulations, but are lax on NOx. In Europe, people don't commute as much, and as long hours, i

> Euro standards are backwards; they have stricter CO2 emissions regulations, but are lax on NOx. In Europe, people don't commute as much, and as long hours, in cars, so I would guess NOx levels in city air don't get as high as in the US cities. So maybe there is no need to have as strict NOx emission limits for cars in Europe.