Preventing Health Risks and Environmental Effects of Air Pollution

Mohammed Abu-Kaff
Environment & Public Health Expert
Dubai Municipality
Dubai – UAE

Introduction

A part from light, water and certain temperature ranges, "clean air" is a prerequisite for the undisturbed development of human beings, animals and plants on earth. Clean air which may still be encountered in areas which have not yet been changed by man's activities contains by volume:

  • 78.10 % of nitrogen (N2)
  • 20.90 % of oxygen (O2)
  • 0.94 % of inert gases (Ar, Kr, Ne, etc.)
  • 0.03 % of carbon dioxide (CO2)
  • 0.01 % of hydrogen (H2)
And there are traces of substances form about 0.0001% of the air volume, among them; Carbon monoxide (CO), Nitrogen oxides (NOX), Ozone (O3), Ammonia (NH3) and Methane (CH4).

These traces substances stem from higher air layers (O3) or are released during decomposition processes or resulted from meteorological effects. Increasing industrialization and density of traffic have, all over the world, led to a considerable increase in air pollution.

Air Pollution

Air pollution (WHO definition) "… is present of an air pollutant or several air pollutants are contained in the outside air in such quantities and for such periods that they become harmful to man, animal, plant or property, contribute to damages or can unduly disturb the wellbeing or the possession of property."

Air-polluting waste products (emissions) from power stations, plants of the chemical and metallurgical industries, domestic fuel and motor traffic are important nuisance factors.

At present, about 300 xenobiotic substances are known to occur in the air, but so far only 20 to 30 of them have been found to be of an economic and hygienic significance. In most cases, gaseous substances possess a high suspenseability and may be widely dispersed by the air current. They are aggressive and may influence reactions in nature more easily than other harmful substances.

1. Air Pollutans

Air pollutants; are substances changing the natural composition of the atmospheric air, they may occur in the following forms:

  • Solid form (dust, soot);
  • Gaseous form (sulphur dioxide, hydrogen fluoride, hydrogen sulphide, nitric oxides, chloride etc.);
  • Liquid or vaporous form (sulphuric acid, tar substances etc.);
  • Aerosols (mixtures of several substances with different states of aggregation).

Gaseous Substance



Much attention must be given to SO2 which is formed during the burning of coal or oil and results from their sulphur content (usually between 0.5 and 4%) and is emitted from all types of furnaces. The amount of SO2 emissions is by far greater than that of other anthropogenic air pollutants. The damages caused by it involve high economic losses. In industrialized countries, these losses account for more than 50% of the overall losses caused by air pollution.

The oxidation of SO2 into SO3 is particularly important, but over long distances sulphur is transported mainly in the form of SO4-2 aerosol. As to the most important harmful substances, mention must be made also of flour compounds which are emanating from a great number of hitherto disregarded sources and can be toxic even at low concentrations.

In towns, a large proportion of air pollution is attributable to more-vehicle exhausts. The amount of harmful substances contained in exhaust gases largely depends on the conditions prevailing during the journey. In case of a strong solar radiation, components of exhaust gases may undergo photochemical reactions triggering off the formation of aggressive compounds. Motor-protective substances which are admixed to gasoline are the cause of a lead load which may often be rather heavy in towns and along much frequented roads.

Dust Air Pollutants

In most cases, dust air pollutants are causing visible pollution effects and are, therefore, noted more frequently. In the air layers adjacent to the ground, the dust content is varying considerably. Due to its surface activity, particles of harmful gases and suspensions of finely dispersed substances may be adsorbed and carried away by soot, which is produced during the incomplete burning of coal and is chemically indifferent. Certain amounts of phytotoxic traces elements (often fluoride) in dusts frequently cause disadvantageous changes in the soil.

Emission of air pollutant dust



The emission concentration is expressed in mg of the harmful substances/m3 of air (formerly ppm; 1 ppm = 2.6 mg SO2 /m3 of air), for dust precipitations in g of dust / m2. 30 days.

Smoke, Aerosols

There are components which are smaller than 1μ; they settle very slowly and are transported over long distances, and their behavior is similar to that of gaseous molecules.

Smog

Smog is a mixture of smoke and fog. It is a fog with great amount of smoke, and it forms haze canopies over industrial towns or densely populated areas. It prevents solar radiation and the warming up of the soil which are necessary in order to eliminate the loaded air layers.

Given the necessary air humidity, condensation nuclei will produce this worst form of air pollution. Smoke, fly ash, dust and gas particles cause a strong obstruction of visibility. In many countries limit values (MIK values) were set in order to limit air pollution.

2. Criteria of Air Pollutants

For determining the allowable concentration of substances in the ambient air, there is a level of concentration which include the most common air pollutants; carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide, which are mainly considered by WHO and EPE because they are endanger public health and the environment, and come from variety sources. The allowable concentration of these pollutants in the air determine according to the time of exposure with no effects on the human organism, and considered as follows:

MIK value; means a "maximum allowable emission concentration", it is the concentration of air pollutants, which, according to the present state of scientific knowledge, generally has no effects on the human organism, provided it is observed or remains under the limit. The MIK values are valid for the sole occurrence of the respective air pollutant.

Short-time values; (MIKK) limit the single or repeated short-time occurrence of air pollutants, the base of reference being the medium concentrations for 15 minutes.

24-hour values; (MIKD) limit the protected single or repeated occurrence of air pollutants, the base of reference being the medium concentrations for 24 hours.

The following table shows the criteria of air pollutants according to maximum allowable immission concentration values valid;



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