Các hạt tương đối lớn khoảng 100 mm đường kính đến trực tiếp từ chất đang được sử dụng (ví dụ như, bụi than, tro, mùn cưa, bụi xi măng, hạt bụi). Khói. Chất rắn lơ lửng thấp hơn 1 mm đường kính thường được phát hành từ quá trình luyện kim hoặc hóa học (ví dụ, oxit kẽm và chì) | AIR POLLUTANTS 35 nitrogen oxides NOy ozone O3 and other oxidants sulfur oxides SxOy and CO2. Pollutant concentrations are usually expressed as micrograms per cubic meter g iir or for gaseous pollutants as parts per million ppm by volume in which 1 ppm 1 part pollutant per million parts 106 of air. Particulate Pollutants. Fine solids or liquid droplets can be suspended in air. Some of the different types of particulates are defined as follows Dust. Relatively large particles about 100 m in diameter that come directly from substances being used . coal dust ash sawdust cement dust grain dust . Fumes. Suspended solids less than 1 m in diameter usually released from metallurgical or chemical processes . zinc and lead oxides . Mist. Liquid droplets suspended in air with a diameter less than m . sulfuric acid mist . Smoke. Solid particles m resulting from incomplete combustion of fossil fuels. Aerosol. Liquid or solid particles m suspended in air or in another gas. Sources of Air Pollutants Natural Pollutants. Many pollutants are formed and emitted through natural processes. An erupting volcano emits particulate matter as well as gases such as sulfur dioxide hydrogen sulfide and methane such clouds may remain airborne for long periods of time. Forest and prairie fires produce large quantities of pollutants in the form of smoke unburned hydrocarbons CO nitrogen oxides and ash. Dust storms are a common source of particulate matter in many parts of the world and oceans produce aerosols in the form of salt particles. Plants and trees are a major source of hydrocarbons on the planet and the blue haze that is so familiar over forested mountain areas is mainly from atmospheric reactions with volatile organics produced by the trees. Plants also produce pollen and spores which cause respiratory problems and allergic reactions. Anthropogenic Pollutants. These substances come primarily from three sources 1 combustion sources that burn fossil fuel for
