Burning Fossil Fuels

Burning of Fossil Fuels

Fossil fuels include petroleum and coal. Burning of coal produces a lot of smoke and dust whereas burning of petrol mainly produces sulphur dioxide. In addition to these, the pollutants include carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides, hydrocarbons, particulate matter and traces of metals.

AutomobilesPetrol on combustion produces carbon monoxide, hydrocarbons, nitrogen oxides, aldehydes, sulphur compounds, organic acids and ammonia and carbon particles. Incomplete combustion of petrol produces a hydrocarbon, 3,4 benzpyrene. There is more pollution during acceleration and deceleration than during constant speed.

Industries

Fertiliser PlantsThey produce oxides, sulphur, nitrogen, hydrocarbons, particulate matter and fluorine. Thermal PlantsSince they are coal based the pollutants are fly ash, soot and sulphur dioxide. Textile IndustriesThey produce cotton dust, nitrogen oxides, chlorine, naphtha vapours, smoke and sulphur dioxide. Steel PlantsThey produce carbon monoxide, carbon dioxide, sulphur dioxide, phenol, fluorine, cyanide, particulate matter, etc.Volcanic eruptions release oxides of nitrogen that pollute the atmosphere. Decomposition of organic matter under anaerobic conditions produces methane which on being oxidised in the atmosphere produces carbon monoxide. Decomposition of these matter also produces foul smelling gases.Photochemical oxidation of marine organic matter and biological oxidation by marine organisms produce lot of carbon monoxide on the surface of the oceans which enters the atmosphere.

Major Pollutants

There are six main categories of air pollutants:

• oxides of carbon• sulphur dioxide• oxides of nitrogen• hydrocarbon• inorganic particulate matter and aerosols• organic particulate matter

Harmful Effects of the Pollutants in AirThe various categories of air pollutants and their harmful effects are summarised in the table following table:

Pollutant Source/Cause Effect

Carbon monoxide

Automobile exhaust, photochemical reactions in the atmosphere, biological oxidation by marine organisms, etc.

Affects the respiratory activity as haemoglobin has more affinity for Co than for oxygen. Thus, CO combines with HB and thus reduces the oxygen-carrying capacity of blood. This results in blurred vision, headache, unconsciousness and death due to asphyxiation (lack of oxygen).

Chlorofluoro carbons (CFCs)

Refngerators, air conditioners, foam shaving cream, spray cans and cleaning solvents.

Destroy ozone layer which then permits harmful UV rays to enter the atmosphere.

Carbon di oxide

Carbon Burning of fossil fuels,depletion of forests (that remove excess carbon dioxide and help in maintaining the oxygen-carbon dioxide ratio).

Global warming as it is one of the greenhouse gases.

Pollutant Source/Cause Effect

Asbestos particles Mining activities Asbestosis - a cancerous disease of the lungs

Biological matter like the pollen grains Flowers Allergy

Fungal spores, bacteria, virus, etc Microbes Infectious deseases

Particulate matter Lead halides (lead pollution)

Combustion of leaded gasoline products Toxic effect in man.

Silicon dioxideStone cutting, pottery, glass manufacturing and cement industries.

Silicosis, a cancerous disease.

Effects of Air Pollution

Global Warming

Most of the solar radiation entering the earth's atmosphere is reflected back into the space. However some of the heat is absorbed by the gases like the carbon dioxide. This serves to keep the earth warm much like the greenhouses. Greenhouses are glasshouses which maintain a temperature higher than the surroundings for the plants to grow and yield better. The other gases that contribute to this are water vapour, methane, chlorofluorocarbons (CFCs) and nitrous oxide. These gases are called the greenhouse gases.

While greenhouse effect is a necessary and natural phenomenon. Every year the temperature are going up due to pollution and the levels of these greenhouse gases is also going up. This is called global warming. According to estimates, at the current rate of increase, the average global temperature will go up by 3oC to 8oC in the next 100 years.This will have the following effects:

Climate of different regionsDistribution of plants and animalsDisturbance in agriculture and food productionMelting of snow caps and resultant increase in sea levels.

Formation of Photochemical Smog

When pollutants like hydrocarbons and nitrogen oxides combine in the presence of sunlight, smog is formed. This is a mixture of gases and since it is formed by photochemical reactions, it is called the photochemical smog. The word 'smog' is derived from the two words-smoke and fog. It forms a yellowish brown haze especially during winter and hampers visibility. It also causes many respiratory disorders and allergies as it contains polluting gases.

Formation of Acid Rain

Sulphur dioxide and nitrogen oxides react with water in the atmosphere producing sulphuric acid and nitric acid. These acids come down along with the rain. This phenomenon is called acid rain. The pH of acid rain varies from 3-6. The composition of acid rain is sulphuric acid, nitric acid and weak carbonic acid.It has the following adverse affects on the environment:•Causes respiratory and skin disorders.•Affects productivity of plants by damaging the leaves.•Enters the soil and affects the soil pH and other conditions.•Enters the ground and river waters which causes harm to the aquatic life.•Causes damage to marble and thus damages buildings and monuments like the Taj Mahal

Aerosol Formation

Aerosol is formed by the dispersion of solid or liquid matter in the atmosphere. There are natural aerosols also in the atmosphere. However, polluting aerosols are formed by the pollutant particulate matter like carbon particles.If the aerosols form a thick layer in the troposphere, they affect the weather conditions by blocking the solar radiation. Aerosols are also deposited on the leaves and affect the photosynthesis. Aerosols disperse the organic metallic pollutants far and wide.

Depletion of Ozone

The stratosphere of the atmosphere has ozone (O3). Ozone is known to absorb the Ultraviolet (UV) rays present in the sun's radiation. The UV rays are believed to cause skin cancer and mutations. Thus, the ozone protects us from the harmful effects of the UV rays.However, hydrocarbons such as the chlorofluorocarbons (CFCs) destroy the ozone molecules which deplete the ozone layer. Ozone holes have been detected in the atmosphere which permit the UV rays to reach the earth's surface. The harmful effects of the UV rays are visible in the countries such as Australia and New Zealand where the rate of skin cancer is higher than the other regions of the world.

Control of Air Pollution

Air pollution can be controlled by different methods depending on the source and the pollutant. The different methods are:One of the major causes of air pollution are the automobiles. The fuels being used should be lead-free as this will reduce the level of lead in the atmosphere. The carburetor should be cleaned regularly and good quality fuel should be used. This reduces the smoke emission from the exhaust pipes of the vehicles. Efforts to introduce vehicles running on alternate sources (for example solar energy) of energy should be made. These methods will go a long way in reducing the occurrence of photochemical smog.

The industrial pollution is best controlled at source. The polluting gases should be passed through filters and other devices such as cyclone collectors, scrubbers, precipitators, etc. so that the particulate matter is removed before the waste gases are released out. The toxic gases should be detoxified.The domestic and industrial smoke producing units should have long chimneys to take the polluting gases far above and then disperse over a larger area. They should also invest in solar cookers or bio gas.

The pollution by sulphur dioxide is mainly due to coal-based industries. Alternate non-sulphur containing fuel must be used. It is also possible to remove the sulphur from the fuel before use.

For effective control and prevention of air pollution it is important to educate people and create public awareness about the ill-effects of air pollution.

The following are some methods that may be adopted to control pollution on a large scale:

CombustionPollutants in the form of organic gases or vapours can be burnt to convert them into water vapour and relatively less harmful products, such as carbon dioxide.

AbsorptionThe gaseous effluents may be made to pass through scrubbers or absorbers. These contain a suitable liquid absorbent, which removes or modifies one or more of the pollutants present in the gaseous effluents making it comparitively harmless.

AdsorptionThe gaseous effluents are passed through porous solid adsorbents kept in suitable containers. The organic and inorganic constituents of the effluent gases are trapped at the interphase of the solid adsorbent. Adsorbents hold (molecules of a gas or liquid or solute) to its surface, causing a thin film to form.

Methods to Control Particulate Emissions

Particulate emissions may be controlled by using mechanical devices that generally work on the basis of the following:

GravityIn this process, the particles settle down by gravitational force. Sudden changes in the direction of the gas flow causes the particles to separate out due to greater momentum.

Fabric FiltersThe gases containing dust are passed through a porous medium. which is usually woven fabrics. The particles present in the gas are trapped and collected in the filters. The gases freed from the particles are then discharged.

Wet ScrubbersWet scrubbers are used in chemical, mining and metallurgical industries to trap sulphur dioxide, ammonia, metal fumes, etc.

Electrostatic PrecipitatorsWhen a gas or an air stream containing aerosols in the form of dust, fumes or mist, is passed between two electrodes, then, the aerosol particles get precipitated on the electrode.

Electrostatic PrecipitatorThe following practices also help in controlling air pollution:Better designed equipment and smokeless fuels must be used in hearths in industries and at home.Automobiles should be properly maintained and must adhere to emission - control standards. (Bharat II or Euro II)More trees should be planted along road-side.Renewable energy sources, such as wind, solar energy, ocean currents, must be tapped to fulfill energy needs.

The following practices also help in controlling air pollution:•Better designed equipment and smokeless fuels must be used in hearths in industries and at home.•Automobiles should be properly maintained and must adhere to emission - control standards. •More trees should be planted along road-side.•Renewable energy sources, such as wind, solar energy, ocean currents, must be tapped to fulfill energy needs.•Tall chimneys should be installed for vertical dispersion of pollutants.