¾ Several major types of air pollution are currently recognized to cause adverse respiratory health
effects: sulfur oxides and acidic particulate complexes, photochemical oxidants, and a
miscellaneous category of pollutants arising from industrial sources.
Sulfur Dioxide and Acidic Aerosols
¾ Sulfur dioxide (SO2) is produced by the combustion of sulfur contained in fossil fuel, such as coal
and crude oil. Therefore, the major sources of environmental pollution with sulfur dioxide are
electric power generating plants, oil refineries, and smelters.
¾ Some fuels, sucZ^}(_}oU]µooÇµo(µ-rich. Ex: China uses it a lot.
¾ Sulfur dioxide is a clear, highly water-soluble gas, so it is effectively absorbed by the mucous
membranes of the upper airways, with a much smaller proportion reaching the distal regions of
¾ The sulfur dioxide released into the atmosphere does not remain gaseous. It undergoes
chemical reaction with water, metals, and other pollutants to form aerosols.
¾ These particulate aerosols vary in composition from area to area, but the most common
pollutants resulting from this atmospheric reaction are sulfuric acid, metallic acid, and
¾ Sulfur dioxide, therefore, together with other products of fossil-fuel combustion forms the
heavy urban pollution that typified old London, many cities in developing nations today that
mainly burn coal.
¾ In addition to this smog t a descriptive term generically referring to the visibly cloudy
combination of smoke and fog t an acidic aerosol is formed that has been shown to induce
asthmatic responses in both adults and children.
¾ In a Harvard study: two measures of air acidity showed significant effects. Higher particle acidity
(nmol/m3) was significantly associate d with an increased risk of bronchitis, while higher levels of
gaseous acids were significantly associated with wheeze attacks, chronic wheezing, and any
¾ Because (SO2) is highly water soluble, nearly all of the inspired (SO2) gas is removed in the upper
airways during rest. Exertion (work and exercising) will increase the fraction of (SO2) gas to the
lower airways and therefore help to precipitate bronchocontriction.
¾ ^oîXî(}^hX^Xv]}vo]µo]Çv(}]Æ]]}ooµvX_ (pg. 21).
¾ In addition to the acute bronchoconstrictive effects of sulfur dioxide, there is epidemiologic
evidence for chronic airway obstruction in persons exposed to elevated levels of (SO2).
¾ Particulate air pollution is closely related to (SO2) and aerosols. The term usually refers to
particles suspended in the air after various forms of combustion or other industrial activity.
¾ In the epidemics noted earlier, the air pollution was characterized by high levels of particulates,
sulfur dioxide, and moisture.