Contaminants are substances that are in some way a determent to comfort, health, and desirable industrial environment. There are three general classes of contaminants:
Solid particles are kept in suspension in air by air currents. Some examples include, dust, fumes, smoke, pollen, bacteria, mold, mists and fogs. There are also gases and vapor contaminants that may behave like true gases. There is little differences between these two impurities. Vapors are gases that have condensing temperatures and pressures close to normal conditions.
Not all contaminants are objectionable or harmful. Perfumes and deodorizers have been used for years. They make the air more pleasant to smell and conceal odors.