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health effects
Introduction / Particulates / Hydrocarbons / Carbon monoxide / Sulphur oxides / Nitrogen oxides / Photochemical oxidants / Other Links / References

It is well documented that air pollution poses a health risk to humans and the environment. People especially vulnerable to air pollution are the very young, the elderly and those with pre-existing disorders like, for example, asthma, emphysema and heart disease. In this section an overview of some of the more prevalent pollutants' health effects are given. These include those related to:

  • particulates,
  • hydrocarbons,
  • carbon monoxide,
  • sulphur oxides,
  • nitrogen oxides, and
  • photochemical oxidants.

At high concentrations, suspended particulate matter poses health hazards to humans, particularly those susceptible to respiratory illness. The success or failure of the human respiratory defense system depends, in part, upon the size of the particulates inhaled and the depth of their penetration in the respiratory tract. Approximately 40% of the particles between 1 and 2 μm in size are retained in the bronchioles and alveoli. Particles ranging in size from 0.25 to 1 μm show a decrease in retention, because many particles in this range are breathed in and out again. However, particles below 0.25 μm show another increase in retention because of Brownian motion, which results in impingement. (Peavy et al., 1985)

Pollens and spores may also cause allergic reactions in sensitive persons. Airborne substances causing allergies are called aeroallergens.

Hydrocarbons in general, and benzene (C6H6) in particular, are carcinogenic (cancer forming) in conditions of long term exposure. Excessive exposure to benzene can also lead to detrimental health affects on the central nervous system.

Although carbon monoxide at low ambient levels has little if any effect on property, vegetation, or materials; it has an adverse effect at higher concentration levels. At higher concentrations, it can seriously affect human aerobic metabolism, owing to its high affinity for hemoglobin, the component of the blood responsible for the transport of oxygen. Carbon monoxide reacts with the hemoglobin (Hb) of blood to give carboxyhemoglobin (COHb), thus reducing the capability of the blood to carry oxygen. Since the affinity of hemoglobin for carbon monoxide is more than 200 times as great as its affinity for oxygen, CO can seriously impair the transport of O2, even when present at low concentrations. The absorption of CO by the body increases with CO concentration, exposure duration, and the activity being performed. (Peavy et al., 1985)

Sulphuric acid (H2SO4), sulphur dioxide (SO2) and sulphate salts tend to irritate the mucous membranes of the respiratory tract and foster the development of chronic respiratory diseases, particularly bronchitis and pulmonary emphysema. In a dusty atmosphere, SO2 is particularly harmful because both sulphur dioxide and sulphuric acid molecules paralyse the hairlike cilia, which line the respiratory tract. Without the regular sweeping action of the cilia, particulates are able to penetrate to the lungs and settle there. (Peavy et al., 1985)

Nitric oxide (NO) is a relatively inert gas and only moderately toxic. Although NO, like CO, can combine with haemoglobin to reduce the oxygen carrying capacity of blood, NO concentrations are generally less than 1,22 mg/m3 (1ppm) in the ambient air and are thus not considered health hazards. However, NO is readily oxidized to NO2, which does have biological significance, as follows (Peavy et al., 1985):

NO + ½O2 <--> NO2 [Equation 1]

NO2 irritates the alveoli of the lungs and may cause decreased pulmonary diffusing capacity. Nitrogen dioxide at high-level exposures of 285 mg/m3 (150ppm) and above, is fatal to humans. (Peavy et al., 1985)

Photochemical oxidants can cause coughing, shortness of breath, airway constriction, headache, chest tightness and soreness, impaired pulmonary function, altered red blood cells, pharyngitis, laryngitis, and eye, nose, and throat irritation in humans. (Peavy et al., 1985)

Heavy traffic raises infant mortality rate

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PEAVY HS, ROWE DR and TCHOBANOGLOUS G (1985) Environmental Engineering. McGraw Hill, New York.

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