Learn about the various effects of air pollution for students and teachers.
1. Effects of Air Pollution on Human Health:
The effects of air pollution on human beings is mainly on eyes and respiratory system. Air-borne gases, vapours, fumes and dust etc., when they come and contact the organs of the body it causes irritation of eyes, nose, throat, and lungs.
(a) Respiratory System:
It consists of lungs and respiratory tract (e.g. tract of air passage from nasal cavity to the lungs). The function of this system is to inhale air into the lungs, filter the impurities from the inhaled air, supply oxygen from the inhaled air to the blood circulatory system and exhale carbon dioxide from the blood through nasal cavity.
If the particulate matter inhaled by the human beings, it will be deposited in various regions of the respiratory system depending on the size of particles. If the size is greater than 10 microns, they are retained by the cilia of the nose. If the size is less than 10 microns, they may enter the upper respiratory tract. The upper respiratory tract consists of nasal cavity, nasal pharynx, larynx and trachea.
The particles of size 2 to 10 microns may enter up to trachea but the movement of cilia sweeps mucus upward, carrying particles from windpipe to mouth, where they can be swallowed. The lower respiratory tract consists of bronchi, bronchioles, alveolar ducts, alveolar sacs and alveoli of the lungs.
Particles of size less than 2 microns are deposited in bronchioles but few of them may reach the alveolar ducts. Particles of size less range from 0.25 to 1 microns enter alveoli of lungs and deposit which reduces the volume of the alveoli thereby causing damage to the lungs by minimising the oxygen exchange from air to blood.
(b) The Eye:
Eye irritation may result when gaseous or particulate material come and contact the external coat of the eye and the internal mucous line of the eye lid. Irritation of eye leads to rubbing which may cause physical damage.
(i) Carbon Monoxide:
Carbon monoxide is a poisonous inhalent. When it is inhaled, it passes through lungs and diffuses into the blood. Carbon monoxide has a strong affinity for combining with the haemoglobin which is present in the blood. The combination of carbon monoxide with haemoglobin leads to formation of carboxy haemoglobin (CoHb).
The affinity of haemoglobin to absorb carbon monoxide is 200 times more than that of oxygen. Therefore, carbon monoxide will be absorbed into the blood instead of oxygen, which reduces the ability of haemoglobin to carry oxygen to the tissues. Due to lack of oxygen (asphyxiation) death can occur. The ambient air quality standard is 10 ppm for 8-h exposure.
At 100 ppm most people experience dizziness, headache. Cigarette smoke contains 400 to 450 ppm of CO. When the CO concentration is greater than 750 ppm, death can occur for a short period (few minutes) of exposure. At 250 to 500 ppm, people will experience the less of consciousness. Generally in urban areas, busy traffic streets contain CO of concentration of 5 to 20 ppm.
Sulphur dioxide can cause irritation, reduction of visibility, respiratory diseases. Healthy persons experience broncho-construction at 1.6 ppm of SO2 for a few minutes exposure. Throat irritation occurs at 8-12 ppm level. 10 ppm can cause eye irritation. At 20 ppm, immediate cough and eye irritation results. Exposure of 400 to 500 ppm of sulphur dioxide even for a few minutes is dangerous to life. Normally urban air contains 0.001 to 0.2 ppm.
Nitric oxide (NO) and Nitrogen dioxide (NO2) are of interest to the concern of human health. NO is not irritant and it will not cause any adverse health effects at atmospheric concentrations. But when NO undergoes oxidation to NO2, it poses health hazards as oxidant. Haemoglobin has 300,000 times affinity for absorbing NO2 than O2, which reduces oxygen earning capacity of the blood.
Nitrogen oxides cause lung tissues to become leathery and brittle and may cause lung cancer and emphysema. Threshold value is 0.12 ppm of NO2. Increased air way resistance occurs at 2 to 5 ppm for 1-h exposure. Nitrogen dioxide at high-level exposures of 150 ppm (285 mg/m3) and above are fatal to humans.
Ozone causes eye irritation when the concentration exceeds 0.1 ppm. Nasal and throat irritation occurs at 0.3 ppm over a period of 8-h exposure. At 1.5 to 2.0 ppm concentrations of 2-h exposure will cause heat pain, coughing and headache. Severe illness will occur at 10 ppm. Photochemical smog consists of air contaminants such as O3, PAN, PBN (peroxy-benzyl nitrate), aldehydes, ketones etc.
Gaseous hydrocarbons play a vital role in the formation of photochemical oxidants.
Generally the following diseases may occur due to air pollution:
1. Lung Cancer:
It is nothing but destruction of lung tissue. Organic carcinogens, specific inorganics like arsenic, asbestos, cadmium, chromium, nickel, and radioactive materials may cause lung cancer.
2. Chronic Bronchitis:
It is the reduction of efficiency of air delivery by reducing the diameter of the bronchioles.
3. Bronchial Asthma:
More responsiveness of the trachea and the bronchi to various stimuli which will occur by narrowing of the airways.
It is due to progressive breakdown of alveolar air sacs in the lungs by chronic infection or irritation of the bronchial tubes, paralysis of the cilia, and injury from violet coughing. Emphysema progressively diminishes the ability of lungs to exchange oxygen and carbon dioxide to blood stream.
2. Effect of Pollutants on Physiological Systems:
The experimental exposure of different types of animals under controlled condition to various concentrations and dosages of air pollutants can provide valuable information regarding the mode of infection of pollutants. Types of effects noticed and measured in human include detection of odour, irritation of eyes, nose and throat, change in pulse rate, breathing frequency, reduction in physical activity and many other physiological responses. Studies of truck drivers, traffic policemen, factory-workers and other occupational groups may give valuable information.
The following pollutants may have some impact on human health:
1. Sulphur Dioxide:
This chemical is produced by making paper and metals. It is an irritant gas which affects the mucous membrane. Some of the air borne sulphur dioxide gas is oxidized to sulphur trioxide. It is also very strong and more irritant than sulphur dioxide, causing severe broncho-spasms at relatively low concentrations.
2. Carbon Monoxide:
Carbon monoxide is produced from the partial oxidation of carbon-containing compounds, mainly from improper burning of various fuels. It causes blood vascular problems and respiratory failure. This gas has a strong affinity for haemoglobin (about two hundred times more affinity than the affinity of oxygen for haemoglobin) and readily binds together to form carboxy-haemoglobin (COHB), reducing the oxygen carrying capacity of the haemoglobin. Carbon monoxide also affects central nervous system. It is also responsible for cardiac arrest.
3. Oxides of Nitrogen:
This chemical is also formed by burning of fuels, like gas, coal, oil and leads to the formation of smog. It is one of the major causal agent of ‘acid rain’ and can damage trees, buildings and monuments. Nitric oxide and nitrogen dioxide are thought to affect human health. Manufacture of nitric acid, high nitrate fertilizer and electric arch welding are the occupations with NO2 hazards. This compound causes problem in the respiratory system. It is estimated that after exposure to about 15 ppm of nitrogen dioxide eye and nasal irritation will be experienced and pulmonary discomfort will start to occur after a brief exposure of 25 ppm.
It is the basic element of smog and causes many different kinds of health issues, related to lung and skin. It can damage plants and limit sight. In contrast to the polluting role of tropospheric ozone, the most obvious cause for concern is the depletion of the stratospheric ozone, as it plays a vital role of filtering the Sun’s ultraviolet radiation. Correlations between the increase in biologically active ultraviolet ray (UV-β) and its estimated ozone loss may affect rates of skin cancer.
It is suggested that everyone per cent decrease of ozone column (O3) will result in a three per cent rise in the incidence of non-melanoma skin cancers, which translates into some 12,000 – 15,000 extra cases a year in the USA, together with a possible one per cent increase in mortality from melanoma.
Exposure to enhanced levels of UV-β can also have other direct harmful effects on the human body, the two most serious being a tendency to suppress the body’s immune response and to cause damage to the eyes, especially in the development of cataracts. Although even more difficult to quantify, it was noticed that these effects would touch all populations, with some consequences- possible increases in the incidence of severity of infectious diseases.
The following effects have been found due to enhanced exposure of UV-β radiation:
Ultra violet-p radiation can initiate a selective down regulation of cell mediated immunity in mammals, including human. Immuno-suppressive effect of UV-β radiation play an important role in UV-β induced skin cancer by preventing the destruction of highly antigenic skin cancer by immune system. A recent report indicated that binding receptor for cis-UCA (transurocanic acid) has been identified as the neurotransmitter 5-hydroxytryptamine (5HT).
ii. Skin Cancer:
There are three main types of skin cancer. Two tend to neutralize and are known as basal and squamous cell carcinoma and are often referred to collectively as non- melanoma skin cancer. The third type, which shows a higher mortality and which can metastasize aggressively is malignant melanoma of which several sub types exist. There is such experimental evidence of a clear connection between sunlight exposure and non-melanoma skin cancer which implicates UV- radiation as a carcinogen.
iii. Non-Hodgkin’s Lymphoma:
Epidemiological evidence suggests that there is a link between non-Hodgkin’s lymphoma and sunlight exposure. This is suggested to be in the immunosuppressive effects of UV-β radiation. A correlation between the occurrence of skin cancer and occurrence of non-Hodgkin’s lymphoma. Lymphatic malignancies, autoimmune diseases (like Type-I diabetes, multiple sclerosis) may also have been an immunosuppressive connection with UV-β radiation.
Cataract is a major cause of blindness. There were estimated 180 million people worldwide who were visually disabled in 2002 and 40-45 million people are blind. Cataract formation is a complicated process with many risk factors. The precise mechanism of action is not known, although UV-β radiation is very strongly implicated and associated with latitude and climate of different countries have been reported. Severe types of cataract exist with a varying degree of association with sunlight. The importance of dietary factors and cataract also require further research.
v. Vitamin D:
Vitamin D or Calciferol is a fat soluble vitamin. It is present in food, but can also be made in human skin after exposure to UV-β radiation from the sun. Many factors can affect vitamin D production such as season, latitude, age, skin colour, sun angle and time spent.
The major function of vitamin D is to maintain normal blood levels of calcium and phosphorus. Vitamin D contributes calcium absorption, helping to form and maintain a strong skeletal structure. Without vitamin D, bones may become thin, brittle, soft or deformed. Vitamin D prevents rickets in children and osteomalacia in adults.
This chemical is used in paint, leaded gasoline, smelters and in lead storage batteries. The main source of lead in atmosphere is the automobile exhausts. It creates urban concentration of inorganic lead of about 1-3 µg/m3, with higher values in area of heavy traffic. Exposure to lead may result in several neural and cerebral disorders and digestive problems. Inorganic lead may cause liver and kidney damage, abnormalities in fertility and pregnancy.
In addition, lead damages the membranes of red blood cell and interferes with the metabolism in a way that shortens the survival of each individual cell, often resulting in anaemia. Research provided evidence that levels of lead exposure associated with central nervous system effects, particularly manifested in behavioral changes.
Insecticides are not only harmful for insects but also have ill- effect on man and its environment. In fact, DDT has been found in mother’s milk in western countries and in our country. According to a study at the Industrial Toxicology Research Centre, Lucknow, the accumulation of pesticides in the environment due to their growing use for agricultural purpose can also cause premature labour and abortion. It can also affect the central nervous system and may attack other vital organs.
viii. Radioactive Isotopes:
The important radioactive isotopes that may reach ambient air .are-iodine, sulphur 35, calcium 45 and uranium. The major source of radioactive air pollutants are nuclear reactors, testing of nuclear bombs, as well as scientific and medical use of radioactive isotopes as tracers. The serious health effects are anaemia, leukaemia and cancer. Radioactive isotopes also cause genetic defects, sterility, embryo defects and congenital malformation.
3. Topographical Effects of Air Pollution:
Oceans, mountains, valleys, and buildings will influence the air motion.
1. Ocean Winds:
Surface topography can effect the sea-breeze either on-shore or off-shore. Along the shore line of the large bodies of water (like sea, lake etc.) during sunny day, the air temperature over the land is more than the ocean because land is heated with faster rate than water.
In the day time (hot sun-rise day), the land heats quickly (absorbs solar radiation fastly) over an unpaved land surface and warm up the air over the land surface to give rise expansion of air. It moves up which creates a low- pressure region and that is occupied by cooler air blowing from the sea. The on-shore sea breeze (breeze from the sea towards shore) develops during the day and reaches peak at mid-afternoon.
After sunset, the temperature of air over the land (shore) decreases with a faster rate because the rate of cooling of earth surface is more than water. At night the ocean is relatively warmer than the land (shore), hence the off-shore breeze develops during night and moves from land to warm sea.
If power plants are located on the sea-coast, the stack effluents will be dispersed over the land during day time by on-shore sea breeze and may be subjected to fumigation (dispersion of pollutants towards ground level).
2. Mountain-Valley Winds:
During day time, air over the base and mountain slopes is heated up by solar radiation and begins to rise and flows over the valley and mountain slopes. After sunset the earth’s surfaces loses solar radiation heat quickly. The cooling of earth surface and air surrounding it give rise to change in density of air. As the night proceeds the air along the valley slopes become dense, colder and moves downward into the valley as a slopes wind. This cold, dense air occupy the valley and tendency to move along the valley axis.
If heavy air pollutant emitting industries are located in the valley, the pollutants are trapped in the valley. During the night the cold air occupied in the valley and warm air occupies at high altitude of the valley. So stable conditions prevail which leads to formation of inversions (trapping of pollutants at a height and they cannot move by stable conditions).
During the day time also the plume (pollutant dispersion) would move up to the valley only. They return to the valley at the nights since the wind shifts towards the lower end of the valley. This circulation of wind may give rise to the build up of the pollutants concentration to dangerous levels.
3. Obstacles Like Buildings:
The characteristics of the land surrounding a stack and the location, non-uniform heights of buildings relative to stack height will influence upon the behaviour of a plume and the generation of mechanical turbulence.
Different types of conditions are presented below:
(i) Location of Stack behind the Hill or Building:
Location of stack or chimney behind a hill may allow the effluents to down wash which is shown in Fig.5.4. But the plume may rise above the stack level. If the stack gas velocity is equal to or less than the ambient velocity, the pollutants may be carried downward on the backside of the stack. Similarly the wind flow pattern around a building is shown in Fig. 5.5.
Due to sudden obstruction (structure), the flow separates to form a cavity behind the building. The backwash of flow is behind the structure. Back flow can occur within the cavity. If pollutant entered in this region, it tends to remain there. If flow reverses in its direction near the ground level, separation can occur on the backside of the building.
(ii) Location of Stack before the Structure (Hill or Building):
When a stack is placed upwind of the hill or building (stack before the structure) wake behind a structure will influence the plume behaviour, as seen in Fig. 5.6(a) and (b).
If the stack height is more as shown in Fig. 5.6(a), the plume may be away from the cavity behind the structure (building). The wake behind the building will help to increase the turbulence so that more dispersion will take place.
If the stack height is not sufficient shown in Fig. 5.6(b), the plume enters the cavity. High pollutant concentrations accumulate along the backside of the building. Hence the designer has to visualise the influence of topography in fixing the stack height. As a thumb rule, stack height, H near the building should be greater than or equal to 2.5 times the height of the building.
4. Effects of Air Pollution:
Effect of air pollution is wider than any other type of pollution, because it travels with the wind. Polluted air affects human and animal health, vegetation, small insects, organisms and environment in general.
Some of the harmful effects of air pollution are:
(i) Effect on human health:
Air pollution affects the human health very easily, as every time we breathe we inhale the polluted air. This goes to the lungs, if carbon monoxide (CO) is present in the air, it mixes with the hemoglobin of the blood and forms carboxy hemoglobin. CO reacts 200 times more than oxygen (O2), thus a small amount of carbon monoxide gas (CO) is sufficient to denature the blood, if CO is inhaled in excess it can be fatal.
Even in this 21st century, such accidents can be seen where, during winters a family sleeps in an unventilated room with a slow-burning fire of coke, and the whole family dies, because of CO gas poisoning. Due to excess of carbon monoxide (CO) in the inhaled air, oxygen bearing capacity of blood decreases which reduces the activity of lungs and brain. Vehicular smoke contains great amount of CO.
Other gases produced by vehicles and inhaled by people are oxides of sulphur and nitrogen. When the polluted air goes to lungs. It causes many diseases like, bronchitis, Asthama, sour throat, burning of eyes and respiratory problems in children.
If the petrol contains lead, then the vehicular smoke becomes more harmful due to lead poisoning. Lead damages liver and kidney muscles and weakens the bones. Other chemicals like hydrocarbons, benzopyrin move in the form of particulate matter may enter the lungs and cause lung cancer.
(ii) Effect on vegetation:
Plants are damaged due to pollution in the air. The dusty and sooty smoke gets deposited on the leaves and fall. The hydrocarbons, oil etc., close the stomata, which affect transpiration and photosynthesis. This can be easily seen, in the plants grown on the divider of a heavy traffic road. They become black and dry.
During the winter and rainy season, the soot and smoke is condensed or runs into the water bodies damaging the vegetation. Acid rain affects the colours of flowers and growth of plants.
(iii) Effect on insects and wildlife:
Air pollution also affects insects and animals, adversely. The insects like honey-bee, butterfly, etc., which are helpful in pollination, are destroyed totally in a polluted area, which reduces the production of a crop, production of apples is seduced due to the reduction in the number of honey-bees.
(iv) Effects on Environment:
(a) Effect on ozone layer:
Ozone layer is a thick layer of ozone gas in stratosphere, which shields the earth from harmful U.V. rays of the Sun. This layer has been depleted by pollutant gases like chlorofluoro carbons (CFC) by 2% during last few years, this is known as ozone hole. The effect of air pollution by CFCS was first observed at Antarctica, where there is much thinning of this layer.
(b) Global warming:
According to an estimate the temperature of the earth has increased by 1% during the last fifty years. This is because of the increase in the percentage of carbon dioxide, oxides of nitrogen and chlorofluoro carbons in the atmosphere. These gases are also known as greenhouse gases. These gases cause undesirable changes in the atmosphere.
(c) Photochemical smog:
The colloidal particles present in the vehicular emission, hydrocarbons, reacts in presence of light forming a photochemical smog, this reduces visibility on roads. Due to this smog in some highly industrialized cities of U.S.A., Britain and Japan, traffic has to be stopped, due to visibility.
The ‘London-smog’ is well known effects of air pollution, where photochemical smog, encircled this industrial city in 1952, for five days, Thousands of people fell ill due to the smog.
(d) Effect of monuments:
The black smoke i.e., soot contains high concentration of hydrocarbons in colloidal form. This gets deposited on the monuments of archaeological importance and deteriorte their upper layer. Taj-Mahal of Agra suffered corrosion due to soot and smoke from Mathura oil refinery, tanneries and other such industries, in the surroundings of Taj. To conserve the beauty of Taj-Mahal, many of the industries have been banned.
5. Effects of Air Pollution on Agriculture:
Air pollution causes adverse effects on human health, buildings, vegetation and agricultural crops, animals, aquatic and terrestrial ecosystems. Apart from these effects, air pollution has adverse effect on the weather conditions of the earth. Air pollution can damage trees, flowers, fruits and vegetables in various ways.
Some pollutants can cause collapse of the leaf tissue, other may bleach or discolour the leaves. The tree foliage are damaged by ozone resulting reduction in growth rate. It has been estimated that ozone alone accounts for 90 per cent of pollution damage to agricultural crops (corn and wheat) amounting to 2 to 3 billion dollars per year in the United States.
Air pollution causes haze, which reduces the visibility caused by scattering of light. In the eastern region of the United States, most of the haze is due to the suspended sulphate particles, but in the western parts, it is usually caused by dust particles, nitrogen oxides or photochemical smog.
Suspended particulates and haze can affect weather conditions by increasing the frequency of fog formation as well as rainfall. The air pollution is of great significance in the long run, because an accumulation of suspended particles in the atmosphere can appreciably reduce the amount of incoming solar radiation.
In fact, this will increase the albedo of the earth and could lead to decline in average global temperatures. But it appears that increase in earth’s albedo is counterbalanced by the green house effect.
6. Effect of Air Pollution on Plant Growth and Yield:
In any region, the plant growth is greatly influenced by climate, soil composition and man. Plant requirements for optimal growth are light, air and temperature for the aerial parts and water, nutrients and soil for the subsoil parts.
The climatic parameters that influence crop growth are temperature, soil moisture, air, light and wind. Human influences on crops are plant selection, land use, cultural practices, water and air pollution.
Pollution is an undesirable change in the physical, chemical or biological characteristics of air, water and soil that may harmfully affect the life or create a potential health hazard of any living organism.
Pollution is thus direct or indirect change in any component of the biosphere that is harmful to the living components and in particular undesirable for man, affecting adversely the industrial progress, cultural and natural assets or general environment.
Any substance, which causes pollution, is called pollutant. A pollutant can also be defined as any solid, liquid or gaseous substance. The main air pollutants are SO2, NOx (Oxides of Nitrogen) and suspended particulate matter (SPM).
The particles of sulphur dioxide (SO2) and nitrogen oxides (NO & NO2) behave like condensation nuclei. The water vapours condense on the surface of these nuclei resulting cloud formation. The dilute solution of sulphuric or nitric acid is produced as the acid gets dissolved in water.
A primary pollutant sulphur dioxide (SO2) undergoes further reaction in sunlight to form sulphur trioxide (SO3). Subsequently SO3 reacts with moisture to form Sulphuric acid mist. Similarly, nitrogen oxide (NO) reacts with oxygen to form nitrous oxide (NO2), which gets converted into nitric acid in the presence of water.
Under such conditions, acid rain occurs in those areas where these pollutants are available in large quantities. The biological effects of these acidic rains on the flora and fauna of lakes are severe. Overall, the damage becomes very heavy, when the pH is less than 6.8 and only few resistant species can survive when the pH is below 5.
Pollutant Stress and Plants:
Major air pollutants causing plant stress, injury and economic loss are photochemical oxidants such as ozone, sulphur dioxide, fluorides and nitrogen dioxide. Recent estimates indicate that 90 per cent or more of the air pollution damage to vegetation in the United States is caused by ozone.
This pollutant and its precursors, oxides of nitrogen and hydrocarbons which result from any fuel combustion, are transported over long distances from urban and industrial areas to rural areas, where crops, forests and other ornamental plants may be damaged.
Other important pollutants are peroxyacetylnitrate (PAN), ethylene, chlorides, acid rain and various particulates. Plants grown in humid climates are more susceptible to ozone and sulphur dioxide than plants grown in arid climates.
Frequently, plant damage is the result of action of pollutant mixtures or interactions of an air pollutant stress with some insect or fungal attack. Species and varieties within species vary significantly in their tolerance to air pollutants, a characteristic frequently used in minimising air pollution losses.
Radiation Stress and Plants:
A deficiency or excess of irradiance may impose a physiological stress on the plant largely through its influence on photosynthesis and related processes. Most plants may be categorised as “shade” plants or “sun” plants. They may also be classified on the basis of their photosynthetic metabolism as C3, C4 and CAM (Crassulacean Acid Metabolism) plants.
Anatomical, ultra-structural, physiological and biochemical differences among these groups of plants are striking and are responsible for ability or inability to adapt to radiation stress in the field.
Solar radiation in the 0.4 to 0.7µ referred to as photosynthetically active radiation (PAR), and red (0.66µ) and far-red (0.73µ)radiation play an essential role in the physiology of higher plants. The intensity, duration and quality of radiation reaching the plant canopy are vital determinants of vegetative growth and crop yields.
The rate of CO2 fixation under saturating PAR in the field, is determined by a number of factors. Two of the most important, are the physical resistance to CO2 diffusion into the leaf and the rate of RuBPc-ase carboxylation. Although various factors are altered by growing plants at different irradiances, there is no agreement as which of these is primarily responsible for the change in photosynthetic capacity observed.
Although, many plants are extremely adaptable to a change in irradiance from solar radiation or artificial light sources, genotype differences in anatomical, biochemical and physiological makeup between “shade” plants and “sun” plants prevent either group from having maximum photosynthetic efficiency under both low and high irradiances.
7. Effects of Air Pollution on Crops:
1. Reduction in root and shoot length,
2. Reduction in the number of leaves per plant,
3. Reduction in biomass, and
4. Reduction in grain yield.
Many studies on the impact of air pollution on plant growth and yield indicate that the environmental factors like light, adequate water supply to the root system, high relative humidity and moderate temperature during the period from morning hours to noon time are favourable for the opening of stomata.
On the other hand most of the plants close their stomata during night. The plants are much more resistant to the pollutants at night than that during day time. Therefore, the plants suffer maximum injury during day as compared to that during night.
iv. Bad Effects of Pollutants:
Sulphur dioxide (SO2) causes yellowing of green leaves. Most of the pigments are destroyed and leaves become white. The leaves become photosynthetically inactive due to bleaching of chlorophyll. The total loss of chlorophyll leads to maximum reduction in productivity.
Fodder plants (clover type) are most sensitive plants whereas wheat, leafy vegetables, beans, strawberries and roses are moderately sensitive plants. But root crops and cabbage are least sensitive plants.
The injury caused by oxides of nitrogen NOx and NO2 is similar to that caused by SO2. Both SO2 and NO2 cause reduction in chlorophyll, root and shoot length, biomass and net productivity in wheat plants.
Coal dust reduces the rate of fruit production and yield by about 90% in mango and lemon trees. Cement dust reduces plant height, stem, number of leaves and bolls per plant in cotton.
v. Beneficial Effects on Crop Yield:
Plants grown under deficiency of S and N are less susceptible to damage by high concentration of SO2 than normal. They give higher yields than those growing under optimal conditions. Crops under certain deficiency conditions are less susceptible to O3 damage. Therefore, ozone (O3) has beneficial effect.
8. Effects on Materials and Property:
Air pollution causes damage on materials and property which is termed as “economic loss”. The damage is mostly on exposed constructional materials like stones, bricks, metals, mortar, wood, paints, electric wirings, and also on rubber, paper, leather and textile materials. These materials may be damaged by the process of (i) abrasion, (ii) chemical attack either directly or indirectly, (iii) deposition, (iv) corrosion, and (v) any combination of above.
Travelling of particulate matter in air with higher velocities cause abrasive action on the obstruction materials. This is due to physical action.
(ii) Chemical Attack:
Pollutants reacts with the material surfaces and make them deteriorate. Some of them may react directly, e.g., bleaching of marble by sulphur dioxide, tarnishing of silver.
Indirect action means that certain materials absorb pollutants and undergo some chemical reactions. The product of the reaction damage the material, e.g., absorption of sulphur dioxide by leather. In the presence of moisture, SO2 in leather produce sulphuric acid, which deteriorates the leather.
Particulate matter deposit on the materials and their aesthetic appearance may be reduced.
Deposition of pollutants on the moistured metal surfaces destroys the protective film of oxygen by electrochemical process. Wind velocity, temperature, moisture, and sunlight will influence the rate of damage.
Sulphur compounds are responsible for the major damage to materials. SO2 is the most detrimental pollutants that contributes to metal corrosion. Aluminium is fairly resistant to SO2 attack. When humidity is more than 70%, corrosion rate is greatly increased.
Hydrocarbons cause no appreciable corrosive damage to materials. Carbon monoxide appears to have no detrimental effect on material surfaces. Paints drying is inhibited by 1 to 2 ppm of sulphurdioxide and paint is blacked by hydrogen sulphide. At 2 ppm, sulphur dioxide causes embrittlement of paper. Textiles of nylon especially nylon hose strength is weakened by sulphur dioxide or sulphuric acid mist aerosol.
9. Effect on Air Pollution – Acid Rain:
“Acid rain” is a broad term used to describe several ways that acids fall out of the atmosphere.
A more precise term is acid deposition, which has two parts – wet and dry. Acid deposition occurs when emissions of sulphur dioxide and nitrogen oxides in the atmosphere react with water, oxygen, and oxidants to form acidic compounds. These compounds fall to the earth in either dry form (gas and particles) or wet form (rain, snow, and fog). In the United States, about 63 per cent of annual SOx emissions and 22 per cent of NOx emissions are produced by burning fossil fuels for electricity generation. Because it typically takes days to weeks for atmospheric SO2 and NOx to be converted to acids and deposited on the earth’s surface, acid deposition occurs in a multistate scale hundreds of miles away from its sources.
Acidity is measured in terms of pH on a logarithmic scale from 1.0 to 14.0. A pH of 1.0 indicates high acidity, whereas a pH of 14.0 indicates high alkalinity; a pH of 7.0 indicates a neutral solution. Precipitation falling through a “clean” atmosphere is normally somewhat acidic, with a pH of about 5.6. Acid rain, however, can have a pH values below 4.0.
In the environment, acid deposition causes soil and water bodies to acidify (making the water unsuitable for some fish and other wildlife) and damages some trees, particularly at high elevations. It also speeds the decay of buildings, statues, and sculptures that are part of our national heritage. The nitrogen portion of acid deposition contributes to eutrophication (oxygen depletion) of water bodies, the symptoms of which include algal blooms (some of which may be toxic), fish kills, and loss of plant and animal diversity.
These ecological changes impact human populations by changing the availability of seafood and creating a risk of consuming contaminated fish or shellfish, reducing our ability to use and enjoy our coastal ecosystems, and causing economic impact on people who rely on healthy coastal ecosystems, such as fishermen and those who cater to tourists.
10. Effect of Air Pollution – Stratospheric Ozone Depletion:
The stratosphere, located about 6 to 31 miles above the earth, contains a layer of ozone gas that protects living organisms from harmful ultraviolet-B radiation (UV-B) from the Sun. UV-B (280 to 315 nanometer wavelength) has been linked to many harmful effects including various types of skin cancer, cataracts, and harm to some crops, certain materials, and some forms of marine life. In the mid–1970s, it was discovered that some human-produced gases could cause stratospheric ozone depletion.
Gases containing chlorine and bromine accumulate in the lower atmosphere, are eventually transported to the stratosphere and then converted to more reactive gases that participate in reactions that destroy ozone. Ozone depletion allows additional UV-B radiation to pass through the atmosphere and reach the earth’s surface, leading to increases in UV-related health and environmental effects.
Several substances have been associated with the stratospheric ozone depletion, including chlorofluorocarbons (CFCs), halons, carbon tetrachloride, methyl bromide, and methyl chloroform. One example of ozone depletion is the annual ozone “hole” over Antarctica that has occurred during the Antarctic spring since the early 1980s.
Rather than being a literal hole, the ozone hole is a large area of the stratosphere with extremely low amounts of ozone. Ozone levels fall by over 60% during the worst years. Even over the United States, ozone levels are about 3 per cent below normal in the summer and 5 per cent below normal in the winter.
11. Effect of Air Pollution – Smog:
“Smog” is a term used in our daily language. It is the mixing of smoke particles from industrial plumes with fog that produces a yellow-black colour near ground level. Under the right conditions, the smoke and sulphur dioxide produced from the burning of coal can combine with fog to create industrial smog. The burning of fossil fuels like gasoline can create another atmospheric pollution problem known as photochemical smog.
Photochemical smog is a condition that develops when primary pollutants (oxides of nitrogen and volatile organic compounds created from fossil fuel combustion) interact under the influence of sunlight to produce a mixture of hundreds of different and hazardous chemicals known as secondary pollutants. Smog is the brownish haze that pollutes our air, particularly over cities in the summertime. Smog can make it difficult for some people to breathe and it greatly reduces how far we can see through the air.
Smog is a mixture of pollutants with ground-level ozone being the main culprit. Increased levels of ground level-ozone are generally harmful to living systems because ozone reacts strongly to destroy or alter many other molecules. Excessive ozone exposure reduces crop yield and forest growth. It interferes with the ability of plants to produce and store food, reducing overall plant health and the ability to grow and reproduce. The weakened plants are more susceptible to harsh weather, disease, and pests. In addition, increases in tropospheric ozone lead to a warming of earth’s surface.
12. Effect of Air Pollution – Visibility Impairment:
Air pollution also has an effect on visibility. Visibility is a measure of aesthetic value and the ability to enjoy scenic vistas, but it also can be an indicator of general air quality. Visibility degradation results when light encounters tiny pollution particles (sulfates, nitrates, organic carbon, soot, and soil dust) and some gases (nitrogen dioxide) in the air.
Some light is absorbed by the particles and other light is scattered away before it reaches the observer. More pollutants mean more absorption and scattering of light, resulting in more haze. Haze obscures the clarity, colour, texture, and form of what we see. Humidity magnifies the haze problem because some particles, such as sulfates, attract water and grow in size, scattering more light.
In the United States’ scenic areas, the visual range has been substantially reduced by air pollution. In eastern parks, average visual range has decreased from 90 miles to 15–25 miles. In the West, average visual range has decreased from 140 miles to 35–90 miles.