Relative Sizes of Particles and Comparison of Dimensional Units

1 micron is a millionth of a meter or 1 inch divided into 25,400 parts.

Substance	Micro-meters (microns)	Inch
90% of Wood smoke particles are smaller than	1 micron	0.00004
Bacteria (average)	2	0.00008
Red Blood Cell	8	0.0003
Talcum Powder	10	0.0004
White Blood Cell	25	0.001
Human Hair	70	0.003
Grain of Table Salt	100	0.004

Particulate pollution in the past decade has been measured as PM10, that is particulate matter 10 microns in diameter or less, which is talcum powder size. Recently the focus has shifted to smaller diameter particles, PM2.5, which denotes all particles 2.5 microns and smaller (bacteria sized). These small sizes are thought to be more injurious because they are deeply respirable, becoming lodged in the farthest recesses of the lungs. Smoke from wood combustion is almost entirely in this range.

"Contribution of wood smoke to air particle pollution. In winter, there is more
air particle pollution caused by wood smoke than any other single source. ... "
www.epa.nsw.gov.au/woodsmoke/default.htm - 23k

Wood smoke particle taken from a human lung enlarged. Original picture size 3 7/8 " by 3 3/8" at 900x enlargement. Chest p.1232. Interstitial Lung Disease and Domestic Wood Burning, Ramage, Roggli, Bell and Piantadosi.

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