Sources of air pollution

In order to control the air pollution it becomes necessary to understand what the sources of air pollution have been and how they operate. Some sources of air pollution have been very large and concentrated; they have been the large factories, chemical plants, oil refiners, metal smelting and recovery works, and electric power stations. However, these have been contributing only one third of the total mass of our air pollution burden. Transportation in the developed countries have been contributing about 45 % with space heating, particularly in winter in the colder countries of Europe and Northern USA and Canada, also making a significant contribution. Within cities it has been the multiplicity of small sources, particularly our private motor cars that are the main cause of the degradation of air quality. The major groups of industrial sources have been oil refining, metal extracting, and the manufacture of chemicals. These and some other industrial air pollution sources will be described separately from simple combustion systems used for industry and electrical power generation, and internal combustion engines used for transportation.

Definitions of selected air pollution terms:

• Dust: A loose term applied to solid particles predominantly larger than colloidal and capable of temporary suspension in air or other gases. Dusts do not tend to flocculate except under electrostatic forces, they do not diffuse but settle under the influence4 of gravity.

• Droplet: A small liquid particle of size and density as to fall under still conditions but which may remain suspended under turbulent conditions.

• Fly ash: The finely divided particles of ash entrained in flue gases arising from the combustion of fuel. The particles of ash may contain incompletely burned fuel.

• Fog: A loose term applied to visible aerosols in which the dispersed phase is liquid. Formation by condensation is usually implied. In meteorology, a dispersion of water or ice.

• Fume: Properly, the solid particles generated by condensation from gaseous state, generally after volatilization from melted substances, and often accompanied by a chemical reaction such as oxidation. Fumes flocculation and sometimes coalesce. Popularly, the term is used in reference to any or all types of contaminants, and in many laws or regulations, with the added qualification that the contaminant has some unwanted action.

• Gas: One of the three states of aggregation of matter having neither independent shape nor volume and tending to expand indefinitely.

• Mist: A loose term to dispersions of liquid particles, the dispersio9n being of low concentration and the particles of large size. In meteorology, a light dispersion of water droplets of sufficient size to be falling.

• Particle: A small discrete mass of liquid or solid matter.

• Smoke: Finely divided aerosol particles resulting from incomplete combustion. Consist mainly of carbon and other combustion material.

• Soot: Agglomerations of particles of carbon impregnated with ‘tar’, formed in the incomplete combustion of carbonaceous material.

• Vapor: The gaseous phase of matter which normally exists in a liquid or solid state.