Table of Contents
- 1 Pollution
- 2 Air Pollution
- 3 Classification of Pollutants
- 3.1 Particulate pollutants
- 3.2 Nanoparticles – NPs
- 3.3 Major Gaseous Air Pollutants, Their Sources & Effects
- 4 Prevention and Control of air Pollution
- 5 Government Initiative
- Pollution may be defined as addition of undesirable material into the environment as a result of human activities. The agents which cause environmental pollution are called pollutants.
- A pollutant may be defined as a physical, chemical or biological substance released into the environment which is directly or indirectly harmful to humans and other living organisms.
- Pollution may be of the following types: Air pollution, Noise pollution, Water pollution, Soil pollution, Thermal pollution and Radiation pollution.
- In order to control environmental pollution, the Government of India has passed the Environment (Protection) Act, 1986 to protect and improve the quality of our environment (air, water and soil).
- Air pollution may be defined as the presence of any solid, liquid or gaseous substance including noise and radioactive radiation in the atmosphere in such concentration that may be directly and/or indirectly injurious to humans or other living organisms, property or interferes with the normal environmental processes.
- An ever increasing use of fossil fuels in power plants, industries, transportation, mining, construction of buildings, stone quarries had led to air pollution.
- Fossil fuels contain small amounts of nitrogen and sulphur. Burning of fossil fuels like coal (thermal power plants) and petroleum (petroleum refineries) release different oxides of nitrogen and sulphur into the atmosphere.
- These gases react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid. The acids drop down with rain, making the rain acidic. This is called acid rain.
- Acid rain corrodes the marble monuments like Taj Mahal. This phenomenon is called as “Marble cancer”.
- Other kinds of pollutants are chlorofluorocarbons (CFCs) which are used in refrigerators, air conditioners and as pressurizing agents in aerosol sprays. CFCs damage the ozone layer of the atmosphere.
- The combustion of fossil fuels also increases the amount of suspended particles in air. These suspended particles could be unburnt carbon particles or substances called hydrocarbons.
- Presence of high levels of all these pollutants cause visibility to be lowered, especially in cold weather when water also condenses out of air. This is known as smog and is a visible indication of air pollution.
According to the form in which they persist after release into the environment.
- Primary pollutants: These persist in the form in which they are added to the environment e.g. DDT, plastic.
- Secondary Pollutants: These are formed by interaction among the primary pollutants. For example, peroxyacetyl nitrate (PAN) is formed by the interaction of nitrogen oxides and hydrocarbons.
According to their existence in nature
- Quantitative Pollutants: These occur in nature and become pollutant when their concentration reaches beyond a threshold level. E.g. carbon dioxide, nitrogen oxide.
- Qualitative Pollutants: These do not occur in nature and are man-made. E.g. fungicides, herbicides, DDT etc.
- Particulate matter suspended in air are dust and soot released from the industrial chimneys. Their size ranges from 0.001 to 500 micrometers (µm) in diameter.
- Particles less than 10 µm float and move freely with the air current. Particles which are more than 10 µm in diameter settle down. Particles less than 0.02 µm form persistent aerosols.
- Major source of SPM (suspended particulate matter) are vehicles, power plants, construction activities, oil refinery, railway yard, market place, industries, etc.
- According to Central Pollution Control Board (CPCB), particulate size 2.5 µm or less in diameter (PM 2.5) are responsible for causing the greatest harm to human health.
- These fine particulates can be inhaled deep into the lungs and can cause breathing and respiratory symptoms, irritation, inflammations and pneumoconiosis – a disease of the lungs due to inhalation of dust, characterized by inflammation, coughing, and fibrosis..
- Fly ash is ejected mostly by thermal power plants as byproducts of coal burning operations.
- Fly ash pollutes air and water and may cause heavy metal pollution in water bodies.
- Fly ash affects vegetation as a result of its direct deposition on leaf surfaces or indirectly through its deposition on soil.
- Fly ash in the air slowly settles on leaves and crops in fields in areas near to thermal power plants and lowers the plant yield.
- Fly ash is now being used for making bricks and as a land fill
- Fly ash particles are oxide rich and consist of silica, alumina, oxides of iron, calcium, and magnesium and toxic heavy metals like lead, arsenic, cobalt, and copper.
- Major oxides are present are Aluminium silicate (in large amounts), silicon dioxide (SiO2) and calcium oxide (CaO).
- Cement can be replaced by fly ash up to 35%, thus reducing the cost of construction, making roads, etc.
- Fly ash bricks are light in weight and offer high strength and durability.
- Fly ash is a better fill material for road embankments and in concrete roads.
- Fly ash can be used in reclamation of wastelands.
- Abandoned mines can be filled up with fly ash.
- Fly ash can increase the crop yield and it also enhances water holding capacity of the land .
Policy measures of MoEF
- The Ministry of Environment and Forests has made it mandatory to use Fly Ash based products in all construction projects, road embankment works and low lying land filling works within 100 kms radius of Thermal Power Station and mine filling activities within 50 kms radius of Thermal Power Station.
Q1. With reference to ‘fly ash’ produced by the power plants using the coal as fuel, which of the following statements is/are correct?
- Fly ash can be used in the production of bricks for building construction
- Fly ash can be used as a replacement for some of the Portland cement contents of concrete
- Fly ash is made up of silicon dioxide and calcium oxide only, and does not contain any toxic elements.
Select the correct answer using the code given below
- 1 and 2
- 2 only
- 1 and 3
- 3 only
Fly ash does contain heavy toxic elements like arsenic, cobalt, lead etc.
Answer: a) 1 and 2
- It is present in petrol, diesel, lead batteries, paints, hair dye products, etc.
- It can cause nervous system damage and digestive problems and, in some cases, cause cancer. Lead affects children in particular.
- Tetraethyl lead (TEL) is used as an anti-knock agent in petrol for smooth and easy running of vehicles.
- The lead particles coming out from the exhaust pipes of vehicles is mixed with air. If inhaled it produces injurious effects on kidney and liver and interferes with development of red blood cells.
- Lead mixed with water and food can create cumulative poisoning. It has long term effects on children as it lowers intelligence.
- Oxides of iron, aluminum, manganese, magnesium, zinc and other metals have adverse effect due to deposition of dust on plants during mining operations and metallurgical processes.
- They create physiological, biochemical and developmental disorders in plants and also contribute towards reproductive failure in plants.
- Nanoparticles are particle with dimensions comparable to 1/109 of a meter [1 divided by 100 crores].
- Major natural processes that release NPs in the atmosphere are forest fires, volcanic eruptions, weathering, dust storms from desert etc.
- Naturally occurring NPs are quite heterogeneous in size and can be transported over thousands of kilometres and remain suspended in the air for several days.
- Nanotechnology has a global socioeconomic value, with applications ranging from electronics to biomedical uses (delivering drugs to target sites).
- Man-made NPs are unknowingly or purposely released in the environment during various industrial and mechanical processes.
- After release in the environment, NPs will accumulate in various environmental matrices such as air, water, soil and sediments including wastewater sludge.
- NPs in the environment influences dust cloud formation, environmental hydroxyl radical concentration, ozone depletion, or stratospheric temperature change.
Effect of NNPs on dust cloud formation
- NNPs are thought to play an important role in dust-clouds formation after being released into the environment as they coagulate and form dust cloud.
- Dust cloud formation decreases sun light intensity.
Asian brown clouds impact on Himalayan glaciers
- Asian brown clouds carry large amounts of soot and black carbon (NPs) which are deposited on the glaciers.
- This could lead to higher absorption of the sun’s heat and potentially contributing to the increased melting of glaciers.
NPs and ozone depletion
- The nanoparticles have greater chemical reactivity. They can result in increased production of reactive oxygen species (ROS), including free radicals like Cl–.
- Radicals like Cl– destroy ozone. [Explained in “Ozone Depletion”]
In chemistry, a radical (a free radical) is an atom, molecule, or ion that has unpaired valence electrons.
Effect of NPs on stratospheric temperature
- NPs in the troposphere interact with molecular hydrogen accidentally released from hydrogen fuel cells and other sources.
- Molecular hydrogen along with NPs moves up to the stratosphere, resulting in the abundance of water vapour in the stratosphere.
- This will cause stratospheric cooling due to formation Stratospheric clouds (mostly ice crystals).
- Stratospheric clouds destroys ozone. [Explained in “Ozone Depletion”]
There is some concern regarding the nanoparticles of some chemical elements that are used by the industry in the manufacture of various products. Why?
- They can accumulate in the environment, and contaminate water and soil.
- They can enter the food chains.
- They can trigger the production of free radicals.
Select the correct answer using the code given below.
- 1 and 2 only
- 3 only
- 1 and 3 only
- 1, 2 and 3
- Carbon monoxide (CO) is a colorless, odorless, tasteless and highly toxic gas that is slightly less dense than air. It is short-lived (stay only few months) in the atmosphere.
- Carbon monoxide is produced from the exhaust of internal combustion engines and from incomplete combustion of various other fuels. Iron smelting also produce carbon monoxide as a byproduct.
- It forms when there is not enough oxygen to produce carbon dioxide (CO2).
- In the presence of oxygen, carbon monoxide burns with a blue flame, producing carbon dioxide.
- Worldwide, the largest source of carbon monoxide is natural in origin, due to photochemical reactions in the troposphere.
- Other natural sources of CO include volcanoes, forest fires, and other forms of combustion.
- Carbon monoxide poisoning is the most common type of fatal air poisoning.
- It is toxic to hemoglobic animals (including humans) when encountered in concentrations above about 35 ppm.
- It is also produced in normal animal metabolism in low quantities.
- It combines with hemoglobin to produce carboxyhemoglobin, which usurps the space in hemoglobin that normally carries oxygen.
- In the atmosphere, it is spatially variable and short lived, having a role in the formation of ground-level ozone (tropospheric ozone) and can elevate concentrations of methane.
- Carbon monoxide reacts with hydroxyl radical (-OH) to produce peroxy radical. Peroxy radical reacts with nitrogen oxide (NO) to form nitrogen dioxide (NO2) and hydroxyl radical. NO2 gives O3 via photolysis (separation of molecules by the action of light).
- Colorless and odorless gas vital to life on Earth. It is heavier than air.
- Natural sources include volcanoes, hot springs and geysers, and it is freed from carbonate rocks by dissolution in water and acids.
- Because carbon dioxide is soluble in water, it occurs naturally in groundwater, rivers and lakes, in ice caps and glaciers and also in seawater.
Effects on Health
- CO2 is an asphyxiant gas (asphyxia → a condition arising when the body is deprived of oxygen, causing unconsciousness or death.).
- Concentrations of 7% may cause suffocation, even in the presence of sufficient oxygen, manifesting as dizziness, headache, and unconsciousness.
Effects on Environment
- Carbon dioxide is an important greenhouse gas. Burning of carbon-based fuels since the industrial revolution has led to global warming.
- It is also a major cause of ocean acidification because it dissolves in water to form carbonic acid.
- Chlorofluorocarbons(CFCs) are used in refrigerators, air conditioners and aerosol sprays.
- Since the late 1970s, the use of CFCs has been heavily regulated because of their destructive effects on the ozone layer. (Explained in a separate post on Ozone Depletion)
- The Montreal Protocol on Substances that Deplete the Ozone Layer (a protocol to the Vienna Convention for the Protection of the Ozone Layer) is an international treaty designed to protect the ozone layer by phasing out the production of numerous substances including CFCs which are responsible for ozone depletion.
- It occurs naturally in the stratosphere. Here it absorbs harmful ultraviolet rays of the sun.
- However, at the ground level, it is a pollutant (Greenhouse gas) with highly toxic effects.
- Vehicles and industries are the major source of ground-level ozone emissions.
- Carbon monoxide, Nitrogen dioxide play a major role in converting O2 to O3.
- Ozone makes our eyes itchy, and watery. It lowers our resistance to cold and pneumonia.
- NOx is a generic term for the various nitrogen oxides produced during combustion.
- They are produced mainly in internal combustion engines and coal burning power plants. They are produced naturally by lightening.
[Oxygen and nitrogen do not react at ambient temperatures. But at high temperatures they produce various oxides of nitrogen. Such temperatures arise inside an internal combustion engine or a power station boiler]
- Agricultural fertilization and the use of nitrogen fixing plants also contribute to atmospheric NOx, by promoting nitrogen fixation by microorganisms.
- NOx (contributes to global cooling) should not be confused with nitrous oxide (N2O), which is a greenhouse gas and has many uses as an oxidizer.
Effects on Health and Environment
- They are believed to aggravate asthmatic conditions and create many respiratory health issues, especially in children.
- The reduction of NOx emissions is one of the most important technical challenges facing biodiesel.
- NOx gases react to form smog and acid rain as well as being central to the formation of tropospheric ozone.
- When NOx and volatile organic compounds (VOCs) react in the presence of sunlight, they form photochemical smog.
- Mono-nitrogen oxides eventually form nitric acid when dissolved in atmospheric moisture, forming a component of acid rain.
- NOx emissions cause global cooling through the formation of -OH radicals that destroy methane molecules, countering the effect of greenhouse gases.
- It is a toxic gas with a pungent, irritating smell. It contributes to acid rain
- It is released naturally by volcanic activity. It is abundantly available in the atmosphere of Venus.
- Sulfur dioxide is primarily produced for sulfuric acid manufacture.
- Inhaling sulfur dioxide is associated with increased respiratory symptoms and disease, difficulty in breathing, and premature death. It also weakens the functioning of certain nerves.
It is also produced by
- burning coal in thermal power plants and diesel fuels.
- some industrial processes, such as production of paper and smelting of metals.
- reactions involving Hydrogen Sulphide (H2S) and oxygen.
- The roasting of sulfide ores such as pyrite, sphalerite, and cinnabar (mercury sulfide). Pollutants
- Volatile Organic Compounds (VOCs) are a large group of carbon-based chemicals that easily evaporate at room temperature.
- For example, formaldehyde, which evaporates from paint, has a boiling point of only –19 °C. Formaldehyde causes irritation to the eyes and nose and allergies.
- The main indoor sources are perfumes, hair sprays, furniture polish, glues, air fresheners, moth repellents, wood preservatives, and other products.
- Health effect – imitation of the eye, nose and throat, headaches, nausea and loss of coordination.
- Long term – suspected to damage the liver and other parts of the body.
- Benzene is a natural constituent of crude oil and is one of the elementary petrochemicals.
- Because benzene has a high octane number, it is an important component of gasoline.
- Benzene increases the risk of cancer and other illnesses. Benzene is a notorious cause of bone marrow failure.
- Ethylene is widely used in the chemical industry. Much of this production goes toward polyethylene, a widely used plastic containing polymer chains of ethylene units in various chain lengths.
- Ethylene is also an important natural plant hormone, used in agriculture to force the ripening of fruits.
- Ethylene is of low toxicity to humans and exposure to excess ethylene cause adverse health effects like headache, drowsiness, dizziness and unconsciousness.
- Ethylene is not but Ethylene oxide is a carcinogen.
- Tobacco smoke generates a wide range of harmful chemicals and is carcinogenic (cancer causing).
- Health effect – burning eyes, nose, and throat irritation to cancer, bronchitis, severe asthma, and a decrease in lung function.
- It includes pollen from plants, mite, and hair from pets, fungi, parasites, and some bacteria.
- Most of them are allergens and can cause asthma, hay fever, and other allergic diseases.
- Asbestos refers to a set of six naturally occurring silicate fibrous minerals –– chrysotile, crocidolite, amosite, anthophyllite, tremolite, and actinolite.
- It is now known that prolonged inhalation of asbestos fibers can cause serious and fatal illnesses including lung cancer, mesothelioma, and asbestosis (a type of pneumoconiosis).
- It is a gas that is emitted naturally by the soil. Due to modern houses having poor ventilation, it is confined inside the house and causes lung cancers.
- Poor ventilation due to faulty design of buildings leads to pollution of the confined space.
- Paints, carpets, furniture, etc. in rooms may give out volatile organic compounds (VOCs).
- Use of disinfectants, fumigants, etc. may release hazardous gases.
- In hospitals, pathogens present in waste remain in the air in the form of spores. This can result in hospital acquired infections and is an occupational health hazard.
- In congested areas, slums and rural areas burning of firewood and biomass results in lot of smoke.
- Children and ladies exposed to smoke may suffer from acute respiratory problems.
- Use of wood and dung cakes should be replaced by cleaner fuels such as biogas, kerosene, LPG or electricity. But supply of electricity is limited. Similarly kerosene is also limited. The use of solar cookers must be encouraged.
- Old stoves must be replaced with improved stoves with high thermal efficiency and reduced emission of pollutants including smoke.
- The house designs should incorporate a well-ventilated kitchen.
- Those species of trees such as baval (Acacia nilotica) which are least smoky should be planted and used. Charcoal is a comparatively cleaner fuel.
- Indoor pollution due to decay of exposed kitchen waste can be reduced by covering the waste properly.
- Segregation of waste, pretreatment at source, sterilization of rooms will help in checking indoor air pollution.
- Industrial pollution can be greatly reduced by:
- use of cleaner fuels such as liquefied natural gas (LNG) in power plants, fertilizer plants etc. which is cheaper in addition to being environmentally friendly.
- employing environment friendly industrial processes so that emission of pollutants and hazardous waste is minimized.
- installing devices which reduce release of pollutants.
- Devices like filters, electrostatic precipitators, inertial collectors, scrubbers, gravel bed filters or dry scrubbers are described below:
- Filters remove particulate matter from the gas stream. The medium of a filter may be made of fibrous materials like cloth, granular material like sand, a rigid material like screen, or any mat like felt pad.
- Baghouse filtration system is the most common one and is made of cotton or synthetic fibres (for low temperatures) or glass cloth fabrics (for higher temperature up to 2900 C).
- There are several ways of removing particulate matter; the most widely used method is electrostatic precipitation, which can remove over 99 per cent particulate matter present in the exhaust from a thermal power plant.
- The emanating dust is charged with ions and the ionized particulate matter is collected on an oppositely charged surface.
- An electrostatic precipitator has electrode wires that are maintained at several thousand volts, which produce a corona that releases electrons.
- These electrons attach to dust particles giving them a net negative charge. The collecting plates are grounded (relatively positive charge) and attract the charged dust particles.
- The velocity of air between the plates must be low enough to allow the dust to fall.
- The particles are removed from the collection surface by occasional shaking or by rapping the surface.
- ESPs are used in boilers, furnaces, and many other units of thermal power plants, cement factories, steel plants, etc.
- It works on the principle that inertia of SPM (suspended particulate matter) in a gas is higher than its solvent and as inertia is a function of the mass of the particulate matter, this device collects heavier particles more efficiently (centrifugation is the technique).
- ‘Cyclone’ is a common inertial collector used in gas cleaning plants.
- Scrubbers are wet collectors. They remove aerosols from a stream of gas either by collecting wet particles on a surface followed by their removal, or else the particles are wetted by a scrubbing liquid.
- The particles get trapped as they travel from supporting gaseous medium across the interface to the liquid scrubbing medium. (this is just like mucus in trachea trapping dust)
- A scrubber can remove gases like sulphur dioxide.
- Proper maintenance of automobiles along with use of lead-free petrol or diesel can reduce the pollutants they emit.
- Catalytic converters, having expensive metals namely platinum-palladium and rhodium as the catalysts, are fitted into automobiles for reducing emission of poisonous gases.
- As the exhaust passes through the catalytic converter, unburnt hydrocarbons are converted into carbon dioxide and water, and carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas, respectively.
- Motor vehicles equipped with catalytic converter should use unleaded petrol because lead in the petrol inactivates the catalyst.
Apart from the use of above mentioned devices, other control measures are –
- increasing the height of chimneys.
- closing industries which pollute the environment.
- shifting of polluting industries away from cities and heavily populated areas.
- development and maintenance of green belt of adequate width.
- The emission standards for automobiles have been set which if followed will reduce the pollution. Standards have been set for the durability of catalytic converters which reduce vehicular emission.
- In cities like Delhi, motor vehicles need to obtain Pollution Under Control (PUC) certificate at regular intervals. This ensures that levels of pollutants emitted from vehicle exhaust are not beyond the prescribed legal limits.
- The price of diesel is much cheaper than petrol which promotes use of diesel. To reduce emission of sulphur dioxide, sulphur content in diesel has been reduced to 0.05%.
- Earlier lead in the form of tetraethyl lead was added in the petrol to raise octane level for smooth running of engines. Addition of lead in petrol has been banned to prevent emission of lead particles with the vehicular emission.
- Usage of alternate fuels like CNG in public transport vehicles is made mandatory in cities like Delhi. All the buses of Delhi were converted to run on CNG by the end of 2002.
- Simultaneously parallel steps taken in Delhi for reducing vehicular pollution include phasing out of old vehicles, use of unleaded petrol, use of low-sulphur petrol and diesel, use of catalytic converters in vehicles, application of stringent pollution- level norms for vehicles, etc.
- The Government of India through a new auto fuel policy has laid out a roadmap to cut down vehicular pollution in Indian cities.
- More stringent norms for fuels means steadily reducing the sulphur and aromatics content in petrol and diesel fuels.
- The goal, according to the roadmap, is to reduce sulphur to 50 ppm in petrol and diesel and bring down the level of aromatic hydrocarbons to 35 per cent.
- The Bharat Stage II (equivalent to Euro-II norms), which is currently in place in Delhi, Mumbai, Kolkata, Chennai, Bangalore, and other major cities was made applicable to all automobiles throughout the country.
- All automobiles in major cities were expected to meet the Euro III emission specifications by 2005 and Euro-IV norms by 2010.
- The rest of the country was expected to meet Euro-III emission norm by 2010.
- According to an estimate, a substantial fall in CO2 and SO2 level has been found in Delhi between 1997 and 2005. But still their levels are not under permissible levels.
- The recent odd-even formula is expected to improve the worsening air quality in Delhi.
- In India, the Air (Prevention and Control of Pollution) Act came into force in 1981, but was amended in 1987 to include noise as an air pollutant. Noise is undesired high level of sound.
- Central Pollution Control Board (CPCB) has been executing a nationwide programme of ambient air quality monitoring known as National Air Quality Monitoring Programme (NAMP).
The National Air Quality Monitoring Programme (NAMP) is undertaken
- to determine status and trends of ambient air quality;
- to ascertain the compliance of NAAQS;
- to identify non-attainment cities;
- to understand the natural process of cleaning in the atmosphere; and
- to undertake preventive and corrective measures.
- The NAAQS have been revisited and revised in November 2009 for 12 pollutants, which include
- sulphur dioxide (S02),
- nitrogen dioxide (NO2),
- particulate matter having micron (PM10),
- particulate matter having size less than 2.5 micron (PM2.5),
- carbon monoxide (CO),
- ammonia, and
- Launched by the Environment Ministry in April 2015.
- Initiative under ‘Swachh Bharat’.
- It helps the common man to judge the air quality within his vicinity.
- Index constituted as a part of Government’s mission to improve the culture of cleanliness.
Old vs new
- While the earlier measuring index was limited to three indicators, the current measurement index had been made quite comprehensive by the addition of more parameters.
Previously who measured Air pollution
- Central Pollution Control Board along with State Pollution Control Boards has been operating National Air Monitoring Program (NAMP).
Why is AQI necessary
- Quality of data from some cities remains weak and the standards set for pollutants fall short of World Health Organization recommendations.
- The pollution related analysis using vast number of complex parameters was complicated for the common man to understand.
Categories of air pollution under AQI
- There are six AQI categories, namely Good, Satisfactory, Moderately polluted, Poor, Very Poor, and Severe.
- The proposed AQI will consider eight pollutants (PM10, PM2.5, NO2, SO2, CO, O3, NH3, and Pb).
- Government is disincentivising use of private vehicles through congestion charging.
- The National Green Tribunal has ordered that diesel vehicles over 10 years old not ply on Delhi roads.
- Odd even formula.
- Making city roads friendly to bicycle users.
- Promoting rooftop solar power as an alternative to coal power.