Particulate matter

Fine solid or liquid particles such as dust, smoke, mist, fumes, or smog, found in air or emissions. The size of the particulates is measured in micrometers (?m). One micrometer is 1 millionth of a meter or 0.000039 inch. Particle size is important because the EPA has set standards for PM_2.5 and PM₁₀ particulates.