The environmental effects of point sources of pollutants, such as industrial plants, depend on many local factors, among which are topography, weather conditions, stack height, location, control equipment, raw materials used, and the type of process. In addition to sulphur dioxide, suspended particulate matter, and oxides of nitrogen, industrial air pollutants include lead, cadmium, mercury, beryllium, the mercaptans and hydrogen sulphide, fluorides, chlorine, asbestos, and many other wastes and by-products of technological processes.