Air pollution is such concentration of solid, liquid or gaseous substance including noise and odour that may cause impairment of health or discomfort to living creatures including human being, plant, property or environment. There are regulations that specify permissible limit of concentration of identified pollutants in the atmosphere.
The atmosphere is a floating storage of gases and water vapours. We inherited an atmosphere created by the nature. This atmosphere with exact quantity of oxygen, nitrogen and Carbon dioxide is our life line. Of late, the atmosphere became polluted basically with various emissions from industrial process and fuel fired vehicles.
As with all natural processes, air has been provided with means to cleanse itself. The water cycle is a good cleanser of atmospheric air by way of evaporation and precipitation. These two processes together scrub the air thoroughly. We witness the end result of such cleansing in the form of acid rain where there is large concentration of Sulfur oxides.. Air pollution becomes unmanageable when pollutant load is large enough to get diluted or cleaned by natural processes.
Air pollution is caused by natural disturbances such as volcano eruption, earthquakes, forest fire as well as human activities such as industrial processes and vehicular emissions. Surprisingly, no creation other than human being, add significantly to air pollution load. On the other hand, they help in mitigating pollution in their own way. Animals eat away all their kills leaving bones which helps in fertilizing the land with Calcium and Phosphate. Birds have also similar schedules. The greenery consumes Carbon dioxide and exhale Oxygen thus improving the air quality. They also absorb and adsorb particulate pollutants. Solar radiation disintegrates many pollutants. Infrared and ultraviolet extremes of solar radiation have great power of annihilating pollutants though these have some contrary contributions too. The moon also plays its little role. The tidal waves catalyzed during full moon period, absorb pollutants floating above the sea.
Human activities are the biggest contributors to pollution load. Like all living creatures, mankind also inhales Oxygen and exhale Carbon dioxide. At present, almost every activity of man is contributing to pollution. Its physical activity of any kind raises the temperature of the environment but that is what for the environment is. Its industrial activity has become a synonym to pollution of every kind. In order to capture more profit in quickest possible time, he has developed technologies aligned to this economics. This generates more waste and lesser end products. Transportation is the key to fast developing and sustained economy. Vehicular emission is one of the biggest contributors to air pollutant loads. Hazardous processes carried out in factories and old, poorly maintained vehicle give out enormous toxic emissions.
Air pollutants have been classified into primary and secondary pollutants. Primaries are those which are directly emitted from a process such as ash from a volcano, Sulfur dioxide from factories and carbon monoxide from a motor vehicle. Indirect emissions are called secondary which form in the air after reaction with the primary pollutants such as ground level Ozone that develops into photochemical smog. Some pollutants may be emitted as primary and as a secondary too. Persistent free radicals, Ammonia, Chlorofluorocarbons, odors, and radioactive substances are also causes of air pollution. Particulate matter also contributes to secondary pollutants,originating from primary gaseous pollutants and compounds in photochemical smog, ground level Ozone and Peroxyacetyl Nitrate. Large number of minor hazardous toxics and persistent organic material adhering to primary pollutants are also present.
Sulfur dioxide is the most prominent oxide of sulfur which is emitted by volcanoes and industrial process. Combustion of coal and petroleum generates Sulfur dioxide. In the presence of Nitrogen dioxide, it forms Sulfuric acid which downpours as acid rain. Nitrogen dioxide, among Nitrogen oxides is emitted from high temperature combustion and is found as reddish brown toxic gas with biting odor. It is a major air pollutant.
Carbon monoxide has no colour, odor or irritating nature but is most lethal if inhaled. It is generated from incomplete combustion of natural gas, wood, and coal Vehicular emission is a major source of CO. Carbon dioxide is also emitted from such combustion and is a major reason for greenhouse effect.
Volatile organic compounds present in the atmosphere have a major role to play in greenhouse gases. Methane is an efficient greenhouse gas. Other hydrocarbons play an important role in creating Ozone and prolonging the life of Methane in the atmosphere. Benzene, Toluene, Xyline and 1,3-butadiene are carcinogen suspects present in VOCs.
Particulate matters(PM) are tiny particles of solids or liquids suspended in a gas. These two together is called aerosol. PM originates naturally from volcano, dust storms, forest fires, vegetations and sea spray or is generated from industrial processes such as fossil fuel combustion in vehicles, power plants, metallurgical and chemical processes and from various construction sites and civil repair. Man generated aerosol is 10% of the total aerosol present in the environment..
Ammonia is another primary pollutant used extensively in synthetic fertilizers for agricultural processes. It is a major compound being used in Pharmaceuticals synthesis. It is both caustic and hazardous.
Traces of toxic materiasl such as Cadmium, Lead and Copper is also found in the air pollutants. Chlorofluorocarbon used in refrigeration and cooling processes impairs the Ozone layer. This has been banned from use. Radioactive pollutants generated from nuclear explosions, natural radioactive decay of Radon and sporadic disaster in nuclear power plants are a serious source of pollution hazards. Odor emanating from sewage, garbage, various industrial processes has also been included as primary pollutants in the statute.
Secondary pollutants are particulate matter formed from primary gaseous pollutants and their compounds present in photochemical smog. Conventional smog results from large scale coal burning and are caused by combination of Sulfur dioxide and smoke. Vehicular emissions and industrial emissions upon reaction with the solar radiation form secondary pollutants combine with primary emission to generate photochemical smog. Ground level Ozone, formed from Nitrogen Oxides and volatile organic matters, is also a constituent of smog which gives rise to photochemical and chemical reactions.
There are some minor air pollutants and number of persistent organic pollutants that pose problem in getting degraded by various chemical, photolytic and biological processes. These have capability to accumulate in human and animal tissues. These biomagnify in food chains. These have adverse effect on the health of human in particular and environment in general.
Air pollution is proving havoc for the health of all living creatures and green lives. Fine particles in air are linked to cardiopulmonary disease which is proving to be major pollutant to cause health impairment and deaths. The next in line is pneumonia related deaths due to pollution from motor vehicles. Other lung diseases associated with the respiratory system such as asthma, lung and heart disease, emphysema and allergies are also attributed to air pollution. Such diseases in children are alarming. A recent study has shown that pesticide spray in air ends up in water bodies and cause problem to man and animal alike including marine life.
Much air pollution related disasters are on record which took many lives. The worst was 1984 Bhopal disaster in India which was due to a massive leak in the Union carbide factory. It killed more than 25,000 people and maimed at least 600,00. The great smog of 1952 in London, U.K., killed more than 12,000 people. An accidental leak of anthrax spore in the erstwhile USSR killed hundreds of people.
Regulatory authorities worldwide stress the need to use improved technologies in which there are minimum emissions. Industrial business houses are adopting such techniques which convert raw material into end product without much wastage. Emissions are put through control devices and the collection in the form of particulates or liquid effluents are further recycled into useful products. For example, coal carbonization procedure has inbuilt technology to collect and recycle ashes to make bricks and cement. Liquid effluent is processed by distillation and other methods to obtain useful byproducts. Solid waste such as tarry residue, coal tar and naphtha are already getting enough attention commercially.
Various equipments and processes are in place to control and contain air pollutants. Particulates are controlled by mechanical collectors such as dust cyclones and multicyclones. In major industries electrostatic precipitators are placed before the final emission to contain ash etc. There are bag houses to handle heavy dust loads. Wet scrubber which washes down particulates from final emissions is another proven control technology. Nitrogen oxides in the emission is reduced to permissible limits by using low NOx burners, selective catalytic/non-catalytic reduction, scrubbers, gas circulation and catalytic converters. Volatile organic constituents are taken care of by absorption systems, flares, thermal/catalytic oxidizers, bio-filters, cryogenic condensers and vapour recovery systems. Wet and dry scrubbers and flue gas desulfurization techniques are in place for control of oxides of sulfur including acid gases. Sorbent Injection technology, electro-catalytic oxidation etc. control mercury in the industrial emissions.
Source: Commercial VOC Mitigation