ABSTRACT
Particle or particulate matter is defined as tiny particles or liquid droplets suspended in the air that can contain a variety of chemical components. Larger particles are visible as smoke or dust and settle out relatively rapidly. The tiniest particles can be suspended in the air for long periods of time and are the most harmful to human health because they can penetrate deep into the lungs. Some particles are directly emitted into the air. Constituting a major class of air pollutants, particulates have a variety of shapes and sizes, and as either liquid droplets or dry dust, they have a wide range of physical and chemical characteristics. Dry particulates are emitted from a variety of different sources in industry, mining, construction activities, incinerators, and internal combustion enginesfrom cars, trucks, buses, factories, construction sites, tilled fields, unpaved roads, stone crushing, and wood burning. Dry particulates also come from natural sources-volcanoes, forest fires, pollen, and windstorms. Other particles are formed in the atmosphere by chemical reactions.
