Air is a mixture of gases composed of approximately 21% oxygen, 78% nitrogen, 1% argon, and traces of other gases. The air we breathe also includes particulate material and gases generated by nature, by man, and by industrial processes as seen in the Figure. We are concerned with the particulate matter and gases which influence our health or comfort, which damage the spaces we occupy, or which effect the products or components we are manufacturing
Measuring Particulate Contamination
The concentration of different size particles in the atmosphere is usually measured by weight or count. A third method, based on the area projection (shadow) of a particle, can be used for relative measurements of the staining portion of atmospheric dust. Methods for testing filters are based on these three techniques.