"Capitol" wrote in message
o.uk...
Simon Brown wrote:

It is poisoning us a lot less than it used to at the height of the
industrial revolution. We just don’t get smog like we used to.T
True, that's why my roof (and drive) is now covered in moss. Not enough
sulphur in the air!

That's the subtle bit.
Moss isn't affected by PMs from diesel engines.
http://en.wikipedia.org/wiki/Particulates