I mentioned this mostly as a reply to:

[3]The caveat is that petrol gas emits particulates at a smaller micron level, unnoticeable to the naked eye, and may actually be of greater concern to the general public.

The diesel exhaust fumes are proven to be worse than the petrol engines in at least one respect - health.

Maybe if every truck on the road and a lot of the cars ran on bananas and not on diesel, then I would be concerned about the radiation levels in bananas.

Moreover in the place where I live people are allowed to remove their car DPFs which makes things even worse.