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3 Classification and Effect of Air Pollutants
Lead-in. Discuss the questions:
Name some of the pollutants.
What harm can they do to the environment?
How can they affect the human health?
According to what criteria can they be classified?
Exercise 1. Read the words, remember the pronunciation.
Consult the dictionary on their meanings.
Fugitive ['fjuidjativ] Exhaust [ig'zo:st]
Deterioration [dUiarie'reiJn] Noxious fnokjas]
Ubiquitous [jufbikwitos] Adverse faedvois]
Carcinogen [ka:'sinod3(a)n] Cellular fseljulo]
Exercise 2. Try to recognize the international words, remember the pronunciation
Dioxide [dai'oksaid] Automobile ['o:temobi:l]
Aerosol ['eorousol] Formaldehyde [fofmasldihaid]
Pesticide ['pestisaid] Acetone ['assi,teun]
Gaseous ['gaesios] Chronic ['kromk]
Herbicide ['hoibisaid] Virus ['vai(o)ros]
Pollutants are the main creators of pollution which cause damage to the target or receptor. Target is always adversely affected by pollutant. It may be man, plant, tree, building, or material.
Air pollutants occur either as gases or particulate matter (PM). PM pollutants are very small particles (1-10 % the diameter of a human hair) of solid or liquid substances. All pollutants may be divided into two main categories: Primary and secondary air pollutants. Primary air pollutants are emitted directly into the air. They include particulates, sulphur dioxide, carbon monoxide, nitrogen oxides, and hydrocarbons. Secondary pollutants are produced by reactions between primary pollutants and normal atmospheric compounds. For example, ozone forms over urban areas when primary pollutants react with sunlight and natural atmospheric gases. Thus, ozone is a secondary pollutant.
According to their sizes and scale stationary sources of pollution are grouped into three categories: point sources, fugitive sources, and area sources. Point sources emit pollutants from one or more controllable sites, such as smokestacks at power plants (Fig. 1). Fugitive sources include dirt roads, construction sites, farmlands, surface mines, and other exposed areas where fire and wind can inject material into air (Fig. 2). Area sources (also called non-point sources) include urban areas, agricultural areas sprayed with herbicides and pesticides, and similar well-defined areas.
Mobile sources emit pollutants while moving from place to place. These include automobiles, trucks, buses, aircrafts, ships, and trains (Fig. 3). Pollutants are generally classified into the following categories:
Gaseous pollutants are gases in nature at normal temperature and pressure. These also include vapors of compounds whose boiling points are below 200 °C. These pollutants include a variety of inorganic and organic gaseous materials.
Inorganic gases include noxious gaseous pollutants like oxides of nitrogen (NO), oxides of sulphur (SO), oxides of carbon, hydrogen sulphide (FIS), ammonia, chlorine, hydrogen fluoride, hydrogen chloride, oxides of phosphorus, hydrogen cyanide, bromine and mercaptans, etc. these primary pollutants are emitted and as such are not found in the atmosphere. Secondary pollutants are also formed in the air and are mainly generated by exhaust of automobiles and industrial emissions.
Organic gases include hydrocarbons and other compounds such as formaldehyde, acetone vapors, alcohols, organic acids, methyl isocyanide, chlorinated hydrocarbons, etc.
Particulate matter is present in atmosphere in fairly large numbers and poses a serious air pollution problem. Particulate pollutants are classified according to their particle size and nature into fumes, dust, ash, carbon smoke, lead, asbestos, mist, spray, oil, grease etc.
Aerosol pollutants remain suspended in air and consist of fine particles of different organic and inorganic compounds having diameter less than 100 jli.
Pesticides are released into the atmosphere mainly by man-made agricultural practices and industrial waste disposal. Run-off from agricultural land contributes these pollutants to water. Today damage from pesticides is increasing enormously and newer hazards are still created. Insecticides, fungicides and pesticides cause considerable environmental deterioration.
Metallic contaminants occur in the atmosphere as a result of industrial activity discharging metals into air, water and soil. Wind or rain also releases metals from soils and rocks of earth’s crust to rivers and seas. Various metals creating environmental hazard are essential dietary trace elements required for growth and development of plants, animals and human beings. These elements are Ca, Al, Ba, Co, Pb, Ag, Ti, Zn etc. Most of the metals are indestructible poisons to living organisms and are ubiquitous in the environment. Examples are Cd, Pb, Cr, Be, Ba, Mn, etc. These are most toxic.
Carcinogens such as benzidine, vinyl chloride, ethylene dichloride etc. present in air cause cancer in man and animal affecting DNA and cell growth.
Radioactive pollutants include particulate and electromagnetic radiations which cause chronic cellular damage in man and animals. Naturally occurring radiations like cosmic and terrestrial radiation enter into biosphere and affect the whole biota. The adverse known effects of radiation are numerous and varied. Radioactive pollution results from nuclear experiments, radioactive elements, drainage from hospitals, industries, and research institutions. Since aquatic flora and fauna can absorb and concentrate radioactivity, the man and animals dependent on them accumulate dangerous amounts of radioactive isotopes.
Biological contaminants deteriorate the atmosphere and their impact on human health is still worst. There exists numerous air borne micro-organisms, pathogens, bacteria, viruses, and parasites which are added as air pollutants in the atmosphere. Their effect on living organisms is obviously undesirable.
Fig. 1. Smokestack pollution
Fig. 2. Fugitive sources of air pollution
Fig. 3. Mobile sources of air pollution
Exercise 3. Consult the dictionary, name the following substances in English
Cd, Pb, Cr, Be, Ba, Mn, Ca, Al, Co, Ag, Ti, Zn.
Exercise 4. Translate from Russian into English
Взвешенные твердые частицы, городская территория, нестойкий источник загрязнения, выхлопы автомобилей, не подвергающийся разрушению, повсеместный, пищевые элементы, канцерогены, ухудшение состояния окружающей среды, первичные загрязнители, неблагоприятно воздействовать.
Exercise 5. Match the category of pollutants with its appropriate representative
Exercise 6. Find the synonyms for the following words in the text
Pollutant, exhaust, aerosol, to create, to release, essential, gas, damage, harmful, negative.
Exercise 7. Match the antonyms from A to В
Exercise 8. Give your definitions of the following terms
Primary pollutants Secondary pollutants Pesticides Point source
Fugitive source Area sources Carcinogen
Exercise 9. Say whether the statements are true or false
Exercise 10. Read the passage through and find the answers to these questions. Remember, you do not have to understand every word to answer the questions.
Through its interdisciplinary environmental teams, industry is directing large amounts of capital and technological resources both to define and resolve environmental challenges. The solution of the complex environmental problems requires the skills and experience of persons knowledgeable in health, sanitation, biology, meteorology, engineering and many other fields.
Each air and water problem has its own unique approach and solution. Restrictive standards necessitate high retention efficiencies for all control equipment. Off-the-shelf items, which were applicable in the past, no longer suffice. Controls must now be specifically tailored to each installation. Liquid wastes can generally be treated by chemical or physical means, or by a combination of the two, for removal of contaminants with the expectation that the majority of the liquid can be recycled. Air or gaseous contaminants can be removed by scrubbing, filtration, absorption or adsorption and the clean gas discharged into the atmosphere. The removed contaminants, either dry or in solution, must be handled wisely, or a new water- or air-pollution problem may result.
Industries that extract natural resources from the Earth, and in so doing disturb the surface, are being called upon to reclaim and restore the land to a condition and contour that is equal to or better than the original state.
Air quality management. The air contaminants which pervade the environment are many and emanate from multiple sources. A sizable portion of these contaminants are produced by nature. The greatest burden of atmospheric pollutants resulting from human activity comprises carbon monoxides, hydrocarbons, particulates, sulphur oxides and nitrogen oxides, in that order. About 50 % of the major pollutants come from the use of the internal combustion engine.
Industrial and fuel combustion sources together contribute approximately 30 % of the major pollutants.
The general trend in gaseous and particulate control is to limit the emissions from a process stack to a specified weight per hour based on the total material weight processed to assure compliance with ambient air regulation. Process weights become extremely large in steel and cement plants and in large nonferrous smelters. The degree of control necessary in such plants can approach 100 % of all particulate matter in the stack. Retention equipment can become massive both in physical size and in cost. The equipment may include high-energy venturi scrubbers, fabric arresters, and electrostatic precipitators. Each application must be evaluated so that the selected equipment will provide the retention efficiency desired.
Sulphur oxide retention and control present the greatest challenges to industrial environmental engineers. Ambient air standards are extremely low and the emission standards calculated to meet these ambient standards place an enormous challenge on the affected industries. Many copper smelters and all coal-fired utility power plants have large volume, weak-sulphur-dioxide gas streams with limestone slurries or caustic solutions is extremely expensive, requires prohibitively large equipment, and creates water and solid waste disposal problems of enormous magnitude. Installations employing dry scrubbing have been used on very low-sulphur-dioxide gas streams.
Copper smelters are required to remove 85-90 % of the sulphur contained in the feed concentrate. Smelters using the old-type reverbatory furnaces produce large volumes of gas containing low concentrations of sulphur dioxide which is not amenable to removal by acid making. However, gas streams from newer-type flash and roaster-electric furnace operations can produce low-volume gas streams containing more than 4 % sulphur dioxide which can be treated more economically to obtain elemental sulphur, liquid sulphur dioxide, or sulphuric acid. Smelters generally have not considered the scrubbing of weak-sulphur-dioxide gas streams as a viable means of attaining emission limitations because of the tremendous quantities of solid wastes that would be generated.
The task of upgrading weak smelter gas streams to produce products which have no existing market has led to extensive research into other methods of producing copper. A number of mining companies piloted, and some have constructed, hydrometallurgical plants to produce electrolytic-grade copper from ores by chemical means, thus eliminating the smelting step. These plants have generally experienced higher unit costs than smelters and a number have been plagued with operational problems. It does not appear likely that hydrometallurgical plants will replace conventional smelting in the foreseeable future. Liquid ion exchange followed by electrowinning, is also being used more extensively for the heap leaching of low-grade copper. This method produces a very pure grade of copper without the emission of sulphur dioxide to the atmosphere.
B. Read the text again carefully. While you read it, look for the answers to these questions.
Exercise 11. Classify the following items into four lists according to their role in environmental engineering. Then find a heading for each list.
Electrolytic grade copper Electrostatic precipitator Electrowinning Fabric arrester Flash furnace Liquid ion exchange
Liquid sulphur dioxide Hydrocarbons Hydrometallurgical plant Nitrogen oxide gases Sulphur dioxide gas Sulphuric acid
Exercise 12. Discuss the following points