Atmospheric Pollution

IUPAC (the International Union of Pure and Applied Chemists) define air pollution as a term covering both natural and man-made sources (i.e. industrial processes and natural events such as wildfires and volcanic eruptions) [1]. The definition goes on to explain that the compound(s) needs to be at a high enough level to interfere with “comfort, health or welfare of persons or the environment” to be considered as air pollution. So, by this definition, the plumes of steam seen rising from power plant cooling towers and so beloved of film makers as an icon of industrial pollution don’t count as air pollution: steam is quite harmless.

In the United States of America, a Federal Agency is responsible for protecting the environment; the Environmental Protection Agency or EPA [2]. It was established in 1970, by the US Government, with a mandate to repair the damage that had been done to the environment and develop the criteria required to deliver a cleaner environment.

According to the Texas Commission on Environmental Quality [3], a facility is considered to be a significant source of air pollution is it emits a ton or more of material per calendar year. A major source of air pollution is the burning of fossil fuels (oil, coal and natural gas) both for the industrial production of electricity, domestic uses including fuel for cars, trucks and aircraft etc and a myriad of other uses.

Although these fuels are essentially organic (composed of hydrogen, carbon and oxygen) they contain other elements which survive the combustion process (e.g. sulphur, nitrogen, phosphorous, arsenic and lead). If a simple organic compound is burned completely, the combustion products are carbon dioxide and water. This is why natural gas (methane) is regarded as a relatively clean fuel source. However, with more complicated hydrocarbons, the burning process is unlikely to be complete, producing smoke, soot and release of the inorganic components contained in the original fuel.

A critical factor in determining the potential harm that airborne pollution can cause to the populace is particle size. The particle size dictates how deeply into the lung a given particle will penetrate. Larger particles do not penetrate deeply into the lung and are effectively excreted, minimising the harm they can do. PM10 (particulate matter with a size below 10 μm or 0.01 mm) has been accepted as a standard to define particles which penetrate deeply into the human lung. Often, PM10 data will be published by municipalities as an index of air quality. Road transport, and notably diesel engine vehicles, is the major sources of PM10 release.

1. IUPAC Compendium of Chemical Terminology 2nd Edition (1997), 1990, 62, 2172.
2. EPA website: (http://www.epa.gov/)
3. Texas Commission on Environmental Quality website: (http://www.tceq.state.tx.us/)