Air Pollution Lecture Notes PDF

GASEOUS POLLUTANTS Perkins (1974) defined air pollution as “air pollution means the presence in the outdoor atmosphere of one or more contaminants such as dust, fumes, gas, mist, odor, smoke or vapour in quantities or characteristics and of duration such as to be injurious to human, plant or animal...

GASEOUS POLLUTANTS Perkins (1974) defined air pollution as “air pollution means the presence in the outdoor atmosphere of one or more contaminants such as dust, fumes, gas, mist, odor, smoke or vapour in quantities or characteristics and of duration such as to be injurious to human, plant or animal life or to property or which unreasonably interferes with the comfortable enjoyment of life and property.” This definition includes only ‘outdoor atmosphere’, but the indoor pollution is more severe these days, because of the emissions from kitchen and faulty planning. Air pollutant Sources Health Effect Environmental Effect Sulphur Oxides Coal and Oil combustion, Reduced lung Sulfur oxide emissions smelters function, increased cause adverse impacts incidence of to vegetation, including respiratory symptoms forests and agricultural and crops diseases, irritation of the eyes, nose, and throat, and premature mortality Oxides Of Nitrogen Fuel and gas combustion Asthma and loss of Acid rain immunity Carbon Monoxide Incomplete petrol and gas Fatal at high doses. Acts like CO2, i.e. traps combustion Attacks the nervous the earth’s heat. system. Hydrogen Sulphide Produced by anaerobic Inhalation of low high acute (short-term) decomposition of organic concentrations may toxicity to aquatic life, matter cause headache, birds, and animals dizziness and upset stomach. At higher concentrations hydrogen sulfide may cause loss of consciousness and death Hydrogen Fluoride Manufacturing of severe respiratory Insufficient data are phosphate fertilizer damage in humans, available to predict the including severe short-term or long-term irritation and effects of hydrogen pulmonary edema. fluoride on aquatic life, plants, birds or land  animals Air pollutant Sources Health Effect Environmental Effect Chlorine and hydrogen Industrial chemical Respiratory irritation harmful to organisms chloride processes which may be fatal living in water and in soil Ozone Photochemical reaction Decreased Impairs the growth of pulmonary function plants due to airway constriction Hydrocarbons Vehicular emissions Cause eye irritation, Produces the dangerous coughing photochemical smog and drowsiness. High molecular weight compounds can be cancer producing (carcinogenic) Lead Petrol combustion, Impairs the mental water pollution, producing batteries, ability cables, solder, paint Suspended Particulate Combustion products matter (fuel, biomass), tobacco smoke  Greenhouse Effect and Global Warming Greenhouse gases are a natural part of the atmosphere. They trap the sun’s warmth, and preserve the earth’s surface temperature at a median level needed to support life. Atmospheric greenhouse gases act like the glass windows of a greenhouse. Sunlight enters the Earth’s atmosphere, passing through greenhouse gases that act like a lens. Then, as it reaches the Earth’s surface, the land, water, and biosphere absorb the sun’s energy. Once absorbed, this energy gets recycled into the atmosphere. A portion of the heat is reflected into space, but a lot of it stays locked in the atmosphere by greenhouse gases, causing the Earth to heat. The figure below shows how these greenhouse gases act in the atmosphere to trap energy. The greenhouse effect describes how atmospheric gases prevent heat from being released back into space, allowing it to build up in the Earth’s atmosphere. The more gases there are, the more the Earth heats up. The greenhouse effect is important. Without it, the Earth would not be warm enough for most living things to survive. However, if the greenhouse effect gets too strong, it can makethe Earth warmer than normal. The problem is that even a little more heat (a few degrees higher) creates problems for people, plants, and animals Greenhouse gases trap energy from the sun in the atmosphere, causing it to heat up. Greenhouse gases We know that the earth is surrounded by a mixture of gases. The Earth’s atmosphere consists of roughly 79.1% nitrogen, 20.9% oxygen, 0.03% carbon dioxide, and trace amounts of other gases. Greenhouse gases are a natural part of the atmosphere. Greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, halogenated fluorocarbons, ozone, perfluorinated carbons, and hydrofluorocarbons. Water vapor is the most important greenhouse gas, but human activity doesn’t have much direct impact on its amount in the atmosphere. Global warming is caused by an increase in the levels of these gases brought about by human activity. The greatest impact on the greenhouse effect has come from industrialization and increases in the amounts of carbon dioxide, methane, and nitrous oxide. The clearing of land and burning of fossil fuels, for example, have raised atmospheric gas concentrations of soot and other aerosols (fine particles in the air). CARBON DIOXIDE Carbon dioxide (CO2) is a natural greenhouse gas and also the biggest human supplied gas to the greenhouse effect (about 70%). A heavy, colorless gas, carbon dioxide is the main gas we exhale during breathing. It dissolves in water to form carbonic acid, is formed in animal respiration, and comes from the decay or combustion of plant/animal matter. Carbon dioxide is absorbed from the air by plants in photosynthesis and is also used to carbonate drinks. NITROGEN OXIDES The colorless gas known as nitrous oxide is an atmospheric pollutant produced by combustion. It is also one of the greenhouse gases. There are several ways that nitrogen and oxygen team up in the atmosphere, including nitrogen dioxide, nitric oxide, and nitrous oxide. Nitrogen oxides are stable gases and do not break down quickly. For this reason, they build up in the atmosphere in greater and greater concentrations. Nitrogen dioxide and other gases and particulates gives the sky that yellow- brown look that many people call smog. Nitrogen combines with moisture in the atmosphere to form nitric acid. This comes down as rain and acidifies lakes and soils, killing fish, and small animal populations and damaging forests. Acid particulates are also precipitated, along with the leaching of heavy metals, into water supplies. Scientists believe that this increase comes from the burning of crops, industrial releases, and the effects of nitrogen fertilizers used in agriculture. METHANE Another greenhouse gas, methane, is a colorless, odorless, flammable hydrocarbon that is released by the breakdown of organic matter and the carbonization of coal. This gas is the second biggest additive, after carbon dioxide, to the greenhouse effect at around 20%. Methane is the main component of natural gas, which is found in deposits, like oil, in the earth’s crust. Methane is a byproduct of the production, transportation, and use of natural gas. Underwater decaying plants create methane known as marsh or swamp gas. One of the best known sources of methane in rural populations is that of belching farm animals. Cows have complicated digestive systems, and release large amounts of methane in satisfying belches. It sounds funny, but when you consider herds of hundreds of animals, it adds up. HALOCARBONS Halocarbons levels dropped since being banned in the 1990s. The phasing out of chlorofluorocarbons has removed a lot of the ozone threat and is allowing the protective ozone layer to recover. However, other problem gases, like perfluorocarbons and sulfur hexafluoride, affect the atmosphere and are given off during aluminum smelting, production of electricity, magnesium processing, and semiconductor manufacturing. Formation of Greenhouse Gases The burning of fossil fuels for energy creates most greenhouse gases. When oil, gas, or coal burns, carbon in the fuel mixes with atmospheric oxygen to form carbon dioxide. Methane is produced from coal mining and certain natural gas pipelines. Animals, especially sheep and cattle, produce methane as food breaks down within their stomachs. Some fertilizers release nitrous oxide. Rice production in paddy fields generates methane under water. When organic matter such as table scraps, garden waste, and paper is left in landfills, its decomposition forms methane and carbon dioxide. Sewage and water treatment plants also release these gases in the process of breaking down wastes. Many industrial processes create greenhouse gases. Cement production, used for everything from building roads to laying the foundations of homes and businesses, requires chemical processes that produce an assortment of greenhouse gases. OZONE Ozone is another major air pollutant but it is not emitted directly from specific sources. It’s formed in the atmosphere from nitrogen oxides and volatile organic compounds (VOCs). Sources of VOCs include: 1. Combustion products from motor vehicles and machinery that burns fossil fuels 2. Gasoline vapors from cars and fueling stations 3. Refineries and petroleum storage tanks 4. Chemical solvent vapors from dry-cleaning processes 5. Solid waste facilities 6. Metal-surface paints CONTROL OF AIR POLLUTION Prevention is always better than cure. So one should try to prevent the air pollution by changing the raw material, the process conditions, procedure and by having the preventive maintenance one can prevent the air pollution. For this purpose some of the examples are as follows:- (i) Controlling the spread of coal dust by sprinkling water on it before handling in a thermal power plant. (ii) Preventive maintenance by repairing leaky valves in advance so as to prevent the leakages of the harmful gases in air. (iii) Applying zoning to distribute the impact of air pollution in a community. (iv) Selection of proper material. For example using low sulfur coal reduces the SO2 problem. In addition to the preventive measures one has to have control technologies as follows. Depending upon the situation different control technologies are adopted. For dealing with the particulate matter the following control technologies are used, Settling chambers Cyclone separators Fabric filters Electrostatic precipitators Wet collector (scrubbers) The first two of the above are used for coarse particulates where as the other three are used for fine particulates. For gaseous pollutants the following control technologies are used. Condensation Absorption Adsorption Combustion For the control of gases such as NO2 and SO2 produced in combustion, wet and dry scrubbers are used. REVIEIW QUESTIONS 1. Fill in the table: Type of gas Pollution effect NOx SO2 Depleting the ozone layer Main contributor to the greenhouse effect  2. List five (5) major air pollutants 3. i. Name the gases that contribute to global warming. ii. Name the gas which does not contribute to global warming. 4. Which combination of gases causes acid rain? 5. Name some of the properties of methane gas. 6. List some of the gases that may be found occurring naturally occurring or produced from organic sources. 7. You are required to use a liquid chemical you know very little of and decide you will review the information provided on the chemical’s MSDS. Identify critical pieces of information you will want to know about and state why. 8. With the aid of a diagram, describe the Greenhouse gas effect. 9. Acid deposition results from which air pollutants? 10. Describe three advantages of using solar energy. 11. State the disadvantages associated with solar energy. 12. Explain how the following gases are produced: Carbon Dioxide, Methane and Chlorofluorocarbons. 13. Complete the following table Control Pollutant Source Technology Two (2) Factors affecting Efficiency Carbon Monoxide ensure complete combustion  - Excess air in early stage of combustion Nitrous Oxides - Ensure high temperature to ensure combustion - High content of nitrogen in fuel Manufacture of napkins, fabrics, foam, bricks etc., Large dust construction dust, sand Mechanical particles blasting Collectors - baffles Bag filters Fine dust particles Electrostatic Precipitator - Speed of flow of dust with air - Electrostatic charge (potential difference) - Frequency of rapping of electrodes 14. Energy derived from wave power is an example of what type of resource? 15. What is the main consequence of increased global atmospheric concentrations of Carbon Dioxide? 16. Define Ozone depletion. What are its causes and effects? 17. Name an example of the measurement of emissions to air from an industrial process 18. Name the device used in an effort to reduce particulate emissions. 19. Which gases are entirely made by humans? 20. Name the gases which cause acid rain? 21. Which gas most contributes to global warming today? 22. Write short notes on the measurement of emissions to air from an industrial process. 23. What is the most important issue to consider when selecting pollution control equipment? 24. What is the main tool used to identify and control the impact of development on the environment? 25. How are hazardous waste records stored; and what is the process involved? 26. Which method is most effective for collecting fly ash (very small particles of dust 27. With the aid of a diagram, describe what is happening to the stratospheric ozone layer? 28. Give the names and sources of greenhouse gases.