1.Particles :

      These are the most widely spread air pollutants. They are given off into the atmosphere from several sources, the most important of which are factory chimneys, laboratories, mills, power stations and furnaces. Smoke evolving from these sources contains fine particles of carbon, ash, oil, grease and metals.

        If these particles are heavy enough to fall, they will start polluting furniture, clothes and bodies. If the are light, they remain suspended in air and can be carried by wind. They cause a decrease in the range of vision. Also these particles may be inhaled into the respiratory system of man and animals. They may settle on plant leaves and so lessen the exposure of these leaves to sunlight. They may even block the stomata of plant leaves and decrease their ability to carry out photosynthesis. As a result, the plant may wilt or even die. Exhaust gases of motor cars may contain completely burned carbon. In addition, motor cars may also add another kind of particle which is rubber resulting from decay tyres.

        A relationship was discovered between the increase in percentage of soot in the air, and the high percentage of pneumonia case. Moreover, some cases of allergy are directly related to the presence of certain particles in the air. Lead particles (which result from the exhaust of motor cars) may affect the nervous system. It has also been observed that Cadmium particles are related to heart diseases, and that the death rate due to this disease increases in cities where air contains a high concentration of this substance in the air. Modern industrial medicine treats many of those diseases that result from inhalation of foreign particles, such as cotton dust which result from ginning, spinning and weaving of cotton. Phosphate dust particles are set up in the air from phosphate mines and factories. Certain hygienic precautions are now applied to protect workers in these factories against these particles.