[Stoves] PM emissions from engines

[Andrew Heggie]

> It does lead to another  question though and that is what is more
> significant, the number of particles or their mass? Plainly if we
> restrict our attention to PM4, as perceived wisdom is larger particles
> are effectively filtered out by the nasal passage, then as particle
> mass goes up with the cube of it's dimensions then a device producing
> many small pm1 particles can emit 8 times as many particles as one
> emitting pm4 before it reaches the same mass.

I meant to say a device emitting PM1 will produce 8 times as many
particles as one emitting pm2  for the same mass, not pm4. It will
emit 64 times as many as one emitting pm4 for the same mass.

Andrew