[Stoves] Particulate size distribution

[Crispin Pemberton-Pigott]

Dear Andrew

At the risk of being corrected by Harold, from whom I learned most of this, I will try to answer.



>>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.

>Are you saying woodsmoke produces very few particles below 2.5?

No, it produces nearly no particles above that cut point. 

If you look at the values for PM1.0 and PM2.5 the latter is about 1% higher. 

The difference between PM2.5 and PM4 as well as PM10 is usually nothing. Tiny differences. 

>>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.

>One of the reports suggested only 40% of the <PM2.5 got exhaled I think.

That will depend of several things including the size. A cigarette is a y-y-yugh source of PM2.5. Does a smoker exhale only 40% of the smoke?

>>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.

>In the past you said the nasal passage was good at stopping PM10, 

Correct. By impact. It turns out the airways are also good at growing the particles by depositing moisture on them making them easier to catch and later expel. 

>...are you now saying this path is likely to make these sizes of concern now?

Yes. Very small particles 10-20 nanometers can diffuse directly through the body.

>>"Differences" in the particles will centre on the chemistry. Actually you can smell the difference over a period of minutes. Diesel smells like diesel.

>Yes, I'm guessing we are mostly concerned with the health risk from sooty (black carbon) particles containing polycylic aromatic compounds. Are these particles full spectrum from <2.5 to >PM10. 

The smoke is highly variable even in one session. 

>What other particles (like fly ash) get detected? Can the two be discriminated?

Sometimes. So far everyone, just about, is happy to hear about PM2.5. 

>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.

Yes. Nothing else to add. 
Crispin 

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