GenerallyThree dramatic episodes of urban pollution in the valley Mause Belgium (1930), in Donora of Pennsylvania (1948) and London (1952) as well as accidents at industrial sites such as Seveso (1976) and Bopal India (1984), showed that in extreme cases the air pollution can cause serious illness or even loss of human life. Nevertheless, the exact relationship of the nature and extent of gaseous pollutants on human health has not been fully determined. The current knowledge is not sufficient to shed light on the problem. Below some information is given which we consider very useful and necessary for humans living in modern societies.
A mature man of medium size breathes about 15 pounds of air and takes less than 1.5 pounds of food and about 2.5 kg of water per day. So, breathing is much more capable of causing health problems in relation to food and water. The air is a gas mixture comprising primarily nitrogen, oxygen and other elements.

Severe air pollution episodes-Mortality
One of the worst episodes of air pollution (no accident) occurred in December 1952 in London. Heavy Freezing fog sat over the city for four consecutive days. This led to increased deaths above the normal levels. Estimated that the number of deaths during 3500-4000 was above the normal levels of a city of 8 million. The causes of deaths were due mainly to lung diseases and heart disease. Positive correlation was found between concentrations of sulfur dioxide (SO2) and smoke with the number of deaths. This incident in London was among the first episodes of air pollution caused by a significant number of deaths. Occasionally occurred elsewhere and other events, highlighting the risks posed by air pollution.
Investigations by the Department of air pollution in the U.S. showed that mortality increased by 20% when the concentration of sulfur dioxide was 1500 mg/M3kai smoke more than 2000 mg/M3.

Mechanisms of action of gaseous pollutants

The effect of air pollution on humans is the result of soil contact with the body. Another effect is that the pollutants absorb solar radiation, thus reducing the intensity of solar rays reaching people and the ionization radiation which comes from certain radioactive isotopes.
Usually the contact of pollutants with the body is the surface of the skin and the exposed films of the body. The sensitivity of the skin plays an important role, except in rare cases, people are particularly susceptible to certain contaminants because of allergy.
Prominent role is played by membranous body surfaces that come in contact with ambient air. The main contact is important because on the one hand, the surfaces are very sensitive and have greater absorption capacity compared with the skin. Gaseous pollutants such as gases, vapors, fumes, dust and other cause irritation of the membranes of eye, nose, respiratory tract, the tracheiovronchial tree and pulmonary parenchyma.
The irritation is manifested in the functioning of the protective mechanism of the body. In the case of the mesh inside of the eyelid and cornea appear as the first symptom and the burning of the eyelids while the generation of tears is an effort to keep the eye clean. The maze of respiratory pipes of the nose force the air to "beat" on the walls of the pipe making these surfaces wet with the hairs of the nose to deduct certain amounts of contaminants. The normal mucoid secretions present in the nasal cavities and pharynx help protect the epithelium (epithelial tissue on the walls of the nose) from irritation from pollutants. The mechanisms of protection of respiratory organs retain particles whose size is more than 5 microns(10 -6 m). Another mechanism is the sense of smell, which helps people to avoid the dangerous environment. Many times, however, the odor does not help protect against pollution, because many contaminants do not smell like carbon monoxide.
Irritant pollutants reaching the throat at high concentrations cause closure of epiglottis (organ separating the larynx from the pharynx) preventing the entrance of contaminated air, thus alerting the recipient to the risk. An important protective mechanism works on the surfaces of membranes of tracheiovronchial tree with mucus production and activation of tassel-like epithelium. The eyelashes are acting as whips and push upwards and out from the throat the various particles. Moreover, the mucus withholds the various gases and with the help of eyelashes trapped gases are pushed to the outside. When they reach the oral cavity, they are either swallowed or expectorated.
The mechanism of the cough acts to remove unwanted particles from the respiratory system. The constant irritation of the lungs leads to the formation of mutated cells. The relationship of these changes can cause lung cancer. Some of the air pollutants produced by fossil fuels and cause health problems are the carbon monoxide(CO), sulfur dioxide (SO2), nitrogen oxides and some carcinogenic substances.

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