Try following a diesel versus a petrol as a cyclist. There are estimates that the push for diesel is directly responsible for tens of thousands of excess deaths in the UK, for example.
"...or my friend's 2009 VW?" When speaking of emissions output, I find it amusing that your anecdata involves a Volkswagen diesel.
This also then led to newer models emitting finer particulate which was more easily picked up by the wind and could travel into the lungs more easily instead of denser particulate which fell to the roadside.