>>and how many of them use diesel fuel?

Agreed that diesel particulates are a health issue, but I've never seen a leaf blower driven by one. Instead, they tend to be 2-stroke engines (that distinctive noise) and what you smell are unburned hydrocarbons. The small 2 stroke engines powering things like backpack blowers tend to do this more than larger ones for reasons I won't get into.

So... hydrocarbons, not particulates. Are the hydrocarbons as bad? I wish I knew - but I do know a n95 won't stop them and a p100 will somewhat.