Air Pollution & Control Module 1
0 likes136 views
This document provides an overview of air pollution sources and characteristics. It discusses that sources can be natural or anthropogenic, and classified as point, area, or line sources. Primary pollutants such as particulate matter, SO2, NOx, CO, and hydrocarbons are emitted directly from sources, while secondary pollutants like ozone and PAN form from chemical reactions. Effects of air pollution include health impacts on humans and vegetation, as well as materials damage. Inversions can trap pollutants by creating stable air conditions. Photochemical smog forms when sunlight reacts with hydrocarbons and NO2 under stagnant air conditions.
Air Pollution & Control Module 1
- 1. AIR POLLUTION & CONTROL 17CV551 By Basavaraj Akki Assistant Professor, Department of Civil Engineering.
- 2. Contents – Module 1 Air Pollution – Definitions Sources of Air Pollution – types Characteristics of air pollutants Effects of air pollution Inversion – types Photochemical smog
- 4. Sources of Air Pollution Sources of air pollution can be grouped into a) A variety of methods including type of source Natural sources include wind blow, dust, pollen grains, sea salt, volcanic gas and ash, forest fire smoke etc.. Anthropogenic sources cover a wide spectrum of types like combustion, roasting & heating processes, food & agriculture industries etc..
- 7. b) Number and spatial distribution of sources include i) Single at point sources (large stationary sources) ii) Area sources (small stationary sources & mobile sources with indefinite routes) iii) Line sources (mobile sources with definite routes)
- 8. c) Types of emissions i) Particulate Matter ii) Gaseous form
- 9. • The variety of matters released into atmosphere by natural and anthropogenic sources is so diverse that it is difficult to classify air pollutants so easily. However usually they are divided into two categories; Primary Pollutants – are those that are emitted directly from the sources Secondary Pollutants – are those formed in the atmosphere by chemical reactions between primary pollutants and atmospheric constituents.
- 10. Primary Pollutants • Primary pollutants are particulate matter such as ash, smoke, dust, fumes, mist & spray; inorganic gases such as SO2, H2S, nitric oxide, ammonia, CO, CO2, hydrogen fluoride, olefinic and aromatic hydrocarbons and also radio-active components. • Of the large no. of primary pollutants into the atmosphere, only a few are present in sufficient concentration to be of major concern. These are 5 major types of particulate matter, SO2, oxides of nitrogen, CO and hydrocarbons. • CO2 is generally not considered as air pollutant, but its increased concentration influences the global climatic patterns which is a major concern.
- 11. Secondary Pollutants • Secondary pollutants are such as SO3, NO2, Peroxy acetyl nitrate (PAN), ozone, aldehydes, ketones and various sulphate & nitrate salts. • Secondary pollutants are formed from the chemical and photo- chemical reactions in the atmosphere. The reaction mechanisms are influenced by many factors such as the concentration of reactants or pollutants, the amount of moisture content, degree of photo- activation, meteorological forces and local photography.
- 12. Properties of Air Pollution 1) Particulate Matter: In general the term particulate refers to all atmospheric substances that are not gases. They can be suspended droplets or solid particles or mixtures of extremely reactive materials ranging from 100µm down to 0.1 µm and less. The inert materials do not react readily with the environment nor do they exhibit any morphological changes as a result of combustion or any other process, where as the reactive materials could be with the environment as a result of combustion or any other process and could be further oxidized. Particulates are classified into Dust, Smoke, Fumes, Mist, Fog, Aerosols etc..
- 13. • Dust: It contains particles of size range 1 to 200 µm. These are formed by natural disintegration of rock & soil. They have large settling velocities and are removed from the air by gravity & other inertial processes. Fine dust particles act as centres of catalysis for many of the chemical reactions taking place in the atmosphere. • Smoke: It contains fine particles of size range 0.01 to 1 µm which can be liquid or solid & are formed by combustion or chemical process. Smoke may have different colours depending on the nature of material burned. • Fumes: These are solid particles of the size range 0.1 to 1 µm and are normally released from chemical or metallurgical processes. • Mist: It is made up of liquid droplets generally smaller than 10µm which are formed by condensation in the atmosphere or released from industrial operation. • Fog: It is the mist in which the liquid is water and is sufficiently dense to obstruct vision. • Aerosol: Under this category are included all air borne suspensions either solid or liquid. These are generally smaller than 1 µm.
- 14. • Particulates in the size range of 1 to 10 µm have measurable settling velocities but are readily disturbed by air movements where as particles of size 0.1 to 1 µm have small settling velocities. • Those below 0.1 µm of sub microscopic size found in urban air undergo random Brownian motion resulting from collision among individual molecules. • Most particulates in urban air have sizes in the range of 0.1 to 10 µm • The finest and the smallest particles are the ones which cause significant damage to health.
- 15. • Oxides of Sulphur: The most important pollutant emitted by pollution sources is SO2. • It is a colourless gas with a characteristic pungent odour. • It is moderately soluble in water (11.3gm/100ml) forming weak sulphuric acid (H2SO3). • It is oxidized slowly in clean air to sulphur trioxide SO3. • In a polluted atmosphere SO2 reacts photochemically or catalytically with other pollutants or normal atmospheric constituents to form SO3 , H2SO4 and salts of H2SO4. • SO3 is generally emitted along with SO2 at about 1-5% of SO2 concentration, SO3 rapidly combines with moisture to form sulphuric acid which has a low dew point. • Both SO2 and SO3 are relatively quickly washed out of the atmospheres by rain or settles as aerosols. • SO3 is responsible for Acid rains.
- 16. • Nitrogen Oxides: of the 6 or 7 oxides of nitrogen only 3 – Nitrous Oxide N2O, Nitric oxide NO & Nitrogen di-oxide NO2 are formed in appreciable quantities in the atmosphere. • N2O is a colourless, odourless, non-toxic gas present in the natural atmosphere in relatively large concentration (0.25 ppm). The major source of N2O is biological activity of the soil. It has a low reactivity and is generally not considered as a Air pollutant. • NO is colourless, odourless gas produced largely by fuel combustion. It is oxidized to NO2 through photo-chemical secondary reactions. • NO2 is a brown pungent gas with an irritating odour which can be detected at concentrations of about 0.12 ppm. It absorbs sunlight and initiates a series of photo-chemical reactions. • It is probably produced by oxidization of NO by ozone or emitted by fuel combustion, hence it is a major concern as a pollutant.
- 17. • Hydro-Carbons: The gaseous and volatile liquid hydrocarbons are of particular interest as air pollutants. Hydrocarbons can be saturated or unsaturated, branched or straight chain or aromatics and other cyclic compounds. (methane, ethylene, propene, benzene, toluene, terpenes) • The Hydrocarbons in air by themselves alone cause no harmful effects. They are of concern because they undergo chemical reactions in the presence of sunlight & nitrogen oxides forming photochemical oxidants of which the predominant one is ozone. • Methane is by far the most abundant hydrocarbons constituting about 40-80% of the total hydrocarbons in the atmosphere but it has a very low photochemical activity as compared to other hydrocarbons. • For this reason, concentration of non-methane hydrocarbons is of interest while considering air pollution
- 18. • Carbon Monoxide (CO): It constitutes the single largest pollutant in the urban atmosphere. • It is colourless, odourless and tasteless and has a boiling point of 0.192°C. • It has strong affinity towards haemoglobin and is a dangerous pollutant. • The rate of oxidation of CO to CO2 in the atmosphere seems to be very slow, mixtures of CO and O2 exposed to sunlight remain almost unchanged. • CO is present in small concentrations of 0.1 ppm in the natural atmosphere and has a residence time of about 6 months. • The main sources of CO in the urban air are smoke, exhaust fumes of many devices, burning coal, gas or oil.
- 19. Effects of Air Pollution All impurities present in air does not cause harm, the prime factors affecting human health are • Nature of pollutants • Concentration • Duration of exposure • State of health of receptor • Age group of receptor An objectionable odour, visibility reduction, eye irritation are useful guides to the health effects.
- 20. Various health effects are • Eye irritation • Throat and nose irritation • Irritation of respiratory tract • Bases like H2S, NH3 and mercaptans cause odour nuisance even at low concentrations • Increase in mortality rate and morbidity rate • Initiation of Asthma attacks • Chronic pulmonary diseases like bronchitis due to high concentration of SO2, NO2, particulate matter
- 21. • CO combines with haemoglobin in the blood and consequently increases stress on those suffering from cardiovascular and pulmonary diseases. It is also a reason for increased heart-attacks. • Hydrogen fluoride causes disease of the bone (Fluorosis) and mattling of teeth. • Carcinogenic agents cause cancer. • Dust particles cause respiratory diseases like Silicosis, asbestosis etc.. • Certain heavy metals like lead may enter body through the lungs and cause poisoning or lead to gastro-intestinal damage or liver/ kidney damage, also affects mental development of children. • Radio-active isotopes like iodine, phosphorous, cobalt, radium, uranium, sulphur, strontium cause serious health effects like anaemia, leukaemia and cancer. They also cause genetic defects and sterility.
- 22. Effects on Vegetation • Air pollution has long been known to have an adverse effect on plants. • The primary factor which controls gas absorption by the leaves is the degree of the opening of the stomata. • Air Pollutants affecting plants are SO2, ozone, Nitrogen oxides, Ammonia, Fluoride compounds, PAN, Herbicides, Smog, Mercury, Ethylene, Hydrogen sulphide, Hydrogen cyanide, Hydrogen chloride.
- 23. Forms of damage to leaves are – • Necrosis – is the killing or collapse of tissue • Chlorosis – It is a loss or reduction of green pigment (chlorophyll) • Abscission – is dropping out of leaves • Epinasty – is the downward curvature of a leaf due to higher rate growth on the upper surface. Kinds of Injury to plants • Acute Injury: It results from short time exposures to relatively high concentrations. Effects are noted within few hours to few days which leads to necrosis. • Chronic Injury: It results from long term low level exposure and usually causes Chlorosis/ abscission. • Growth/ Yield Retardation: Here the injury is in the form of an effect on growth without visible markings usually suppression of growth/ yield occurs.
- 24. Air Pollutants Dose Effects on Vegetation/ Plants Nitrogen dioxide Mild Suppressed growth, leaf bleaching Ethylene Mild Epinasty, Abscission PAN Mild Bronzing of lower leaf surface, suppressed growth Sulphur dioxide Mild Interveinal chlorotic bleaching of leaves Severe Necrosis Ozone Mild Premature aging, suppressed growth Severe Collapse of leaf, Necrosis, Bleaching Fluorides Cumulative effects Necrosis at leaf tip
- 25. Effects on Materials • Air Pollution cause damage to materials by 5 mechanisms- 1. Abrasion 2. Deposition & Removal 3. Direct chemical attack (bleaching of marble by SO2, tarnishing of silver by H2S) 4. Indirect chemical attack & 5. Corrosion in the presence of moisture. • Factors affecting are; Moisture in the atmosphere, Temperature, Sunlight and Air Movement/ Wind speed.
- 26. Materials Air Pollutants Effects 1. Metals SO2, Acid gases Corrosion, loss of metal, spoilage of surface, tarnishing 2. Building Materials SO2, Acid gases, Particulates Discoloration, leaching 3. Paint SO2, H2S, Particulates Discoloration 4. Textiles and Textile dyes SO2, Acid gases, NO2, Ozone Fading, reduces textile strength 5. Rubber Oxidants, ozone Cracking, weakening. 6. Leather SO2, Acid gases Disintegration, powdered surface 7. Paper SO2, Acid gases Embrittlement 8. Ceramics Acid gases Change in surface appearance
- 27. Inversions • Temperature inversion, is a reversal of the normal behaviour of temperature in the troposphere, in which a layer of cool air at the surface is overlain by a layer of warmer air. (Under normal conditions, temperature usually decreases with height).
- 28. • Inversions play an important role in determining cloud forms, precipitation, and visibility. • An inversion acts as a cap on the upward movement of air from the layers below. As a result, convection produced by the heating of air from below is limited to levels below the inversion. • Diffusion of dust, smoke, and other air pollutants is likewise limited. • Visibility may be greatly reduced below the inversion due to the accumulation of dust and smoke particles. • Since air near the base of an inversion tends to be cool, fog is frequently present there.
- 29. Radiation inversions • Radiation inversions are the most common type of inversion. In some places, they occur almost nightly. • Radiation inversions generally happen in places where it cools off a lot at night. • During the night, the ground cools off, radiating the heat to the sky. Hence, an inversion • It is because of radiation inversions that there is often fog in the morning. • The radiation inversion traps the moisture (clouds) under the inversion layer resulting in for or smog, depending where you live.
- 30. Subsidence inversion • A subsidence inversion develops when a widespread layer of air descends. The layer is compressed and heated by the resulting increase in atmospheric pressure, and as a result the lapse rate of temperature is reduced. • If the air mass sinks low enough, the air at higher altitudes becomes warmer than at lower altitudes, producing a temperature inversion. • Subsidence inversions are common over the northern continents in winter and over the subtropical oceans; these regions generally have subsiding air because they are located under large high-pressure centres. • Due to inversion of temperature, air pollutants such as dust particles and smoke do not disperse in the valley bottoms.
- 31. • Because of these factors, houses and farms in intermontane valleys are usually situated along the upper slopes, avoiding the cold and foggy valley bottoms. For instance, coffee growers of Brazil and apple growers and hoteliers of mountain states of Himalayas in India avoid lower slopes. • Fog lowers visibility affecting vegetation and human settlements. • Less rainfall due to stable conditions.
- 33. Photo-chemical Smog • It was first observed in Los Angeles, USA in the mid 1940’s. • The condition for formation of photo-chemical smog are air stagnation, abundant sunlight, high concentration of hydrocarbons & NO2