[Stoves] News 24 Jan 2017: Dirty woodstoves cause a health crisis in London

Crispin Pemberton-Pigott crispinpigott at outlook.com
Tue Jan 31 10:18:23 CST 2017


Dear Andrew

With reference to PM sizes: wood and coal fires make particles which have a central 'mass' of PM0.6. Half the mass is above and half below a great deal of the time during tests. In other words they are small.

There are few particles in the size of PM2.5 which is why that number was chosen. If the equipment is a little off it makes nearly no difference to the mass detected.

I have quite a number of tests made using a GRIMM 11-R which gives size 'bins' and the size profile can be easily seen. The GRIMM fortunately reports counts as well as the mass if a density is supplied. The density can be applied per bin so it can be calibrated very well - far better than a Dusttrak which reports PM1.0, PM2.5, PM4 and PM10.

The cleaning up of diesel emissions was in large part the reduction of PM size below the detection limit of optical instruments. Two things have resulted: equipment that can now detect optically to a much smaller particle, and even better combustion.

The health and social impact of nanoparticles is not well known at all. The idea that they penetrate deep into the lungs hides the fact they are also expelled very easily. A major concern is the nasal passages provide a direct path by diffusion to the brain, which dispenses with lung arguments.  They also enter the lung cells by diffusion of course.

"Differences" in the particles will centre on the chemistry.  Diesel particles will be far more homogeneous that wood smoke particles which will vary a great deal during the process of a burn. Actually you can smell the difference over a period of minutes. Diesel smells like diesel.

Back to the distribution, obviously an equal mass below 0.6 microns will have a heck of a lot more particles than above 0.6. As we move forward it is likely the metrics will change from mass or mass-equivalent to counts and size.

Regards
Crispin





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