"Nightjar" wrote in message
...
On 05/05/2018 08:20, harry wrote:
On Friday, 4 May 2018 12:24:03 UTC+1, Nightjar wrote:
...
From that, London figures for SPM in micrograms per cubic metre a

2016 - 16
1980 - 82
1970 - 124
1960 - 167
1950 - 209
1940 - 368
1900 - 571

Very small particles are more dangerous. As from diesel engines.

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.

But its far from clear that there is any real health problem
from those, let alone that they are relevant for asthma.

The earlier figures will include very significant levels of soot particles
from coal burning as well.