On 05/05/2018 09:35, Nightjar wrote:

85% of PM2.5 particles generated by road traffic are from non-exhaust
sources; predominantly tyre wear, road wear and the raising of dust from
the road surface. Those come from all vehicles, whatever their motive
power. The earlier figures will include very significant levels of soot
particles from coal burning as well.

Source?

I've often been behind a diesel smoking enough to make me put the air on
recirc - most recently this evening. I've never had it from tyres or dust.

Andy