Particulate matter dust storms

Dust storms that entrain large amounts of particulate matter are a common natural source of air pollution in many parts of the world. Even a relatively small dust storm can result in suspended particulate matter read-... 

The particles and droplets that make up particulate matter range widely in size. Some are large enough to he seen, such as the tiny particles of sand stirred up in a dust storm. Others are so small as to be invisible to the naked eye. In general, these particles and droplets are divided into two major categories, based on their size. Particles designated as PM2 5 have diameters less than or equal to 2.5 p (microns or micrometers) in diameter. Particles with diameters between 2.5 p and 10 p are designated as PMj particulates. The terms fine and coarse are sometimes used to described PM2 5 and PMjq particulates, respectively. 

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