What is Air Pollution? It is an atmospheric condition in which certain substances (including the normal constituents in excess) are present in concentrations, which can cause undesirable effects on living beings and the environment. These substances include gases, particulate matter, radioactive substances, etc. The question is Briefly describe the sources, effects, and control of air pollution. Air pollution is a change in the physical, chemical and biological characteristics of air that causes adverse effects on humans and other organisms. The ultimate result is a change in the natural environment and/or ecosystem.
What are the natural and man-made pollutants that cause air pollution? The discussion of the sources, effects, and control of air pollution.
Gaseous pollutants include oxides of sulfur (mostly S02, S03) oxides of nitrogen (mostly NO and N02 or NOx), carbon monoxide (CO), volatile organic compounds (mostly hydrocarbons), etc. Particulate pollutants include smoke, dust, soot, fumes, aerosols, liquid droplets, pollen grains, etc. Radioactive pollutants include radon-222, iodine-131, strontium-90, plutonium-239, etc.. The substances that are responsible for causing air pollution are called air pollution. These air pollutants can be either natural (e.g. wildfires) or synthetic (man-made); they may be in the form of gas, liquid or solid.
Sources of Air Pollution:
Sources of air pollution refer to the various locations, activities or factors which are responsible for the release of pollutants in the atmosphere. The sources of air pollution are natural and man-made (anthropogenic).
1] Natural Sources:
The natural sources of air pollution are volcanic eruptions, forest fires, sea salts sprays, biological decay, photochemical oxidation of terpenes, marshes, extraterrestrial bodies pollen grains of flowers, spores, etc. Radioactive minerals present in the earth’s crust are the sources of radioactivity in the atmosphere.
The following natural sources of air pollution below are:
- Dust from natural sources, usually large areas of land with little or no vegetation.
- Methane, emitted by the digestion of food by animals, for example, cattle.
- Radon gas from radioactive decay within the Earth’s crust. Radon is a colorless, odorless, naturally occurring, radioactive noble gas that forms from the decay of radium.
- It considers being a health hazard. Radon gas from natural sources can accumulate in buildings, especially in confined areas such as the basement and it is the second most frequent cause of lung cancer, after cigarette smoking.
- Smoke and carbon monoxide from wildfires.
- Volcanic activity, which produces sulfur, chlorine, and ash particulates.
Man-made sources include thermal power plants, industrial units, vehicular emissions, fossil fuel burning, agricultural activities, etc. Thermal power plants have become the major sources for generating electricity in India, as nuclear power plants couldn’t install as plan. The main pollutants emitted are fly ash and S02. Metallurgical plants also consume coal and produce similar pollutants. Fertilizer plants, smelters, textile mills, tanneries, refineries, chemical industries, paper, and pulp mills are other sources of air pollution.
Automobile exhaust is another major source of air pollution. Automobiles release gases such as carbon monoxide (about 77%), oxides of nitrogen (about 8%) and hydrocarbons (about 14%). Heavy-duty diesel vehicles spew more NOx and suspended particulate matter (SPM) than petrol vehicles, which produce more carbon monoxide and hydrocarbons.
3] Indoor Air Pollution:
The most important indoor air pollutant is radon gas. Radon gas and its radioactive daughters are responsible for a large number of lung cancer deaths each year. The Radon can emit from building materials like bricks, concrete, tiles, etc., which are deriving from soil containing radium. Radon is also present in groundwater and natural gas and emits indoors while using them.
Many houses in the under-developed and developing countries including India use fuels like coal, dung-cakes, wood, and kerosene in their kitchens. Complete combustion of a fuel produces carbon dioxide, which may not be toxic. However, incomplete combustion produces toxic gas carbon monoxide. Coal contains varying amounts of sulfur, which on burning produces sulfur dioxide.
Fossil fuel burning produces black soot. These pollutants i.e. CO, sulfur dioxide, soot and many others like formaldehyde, benzo- (a) pyrene (BAP) are toxic and harmful for health. BAP is also found in cigarette smoke and considered to cause cancer. A housewife using wood as fuel for cooking inhales BAP equivalent to 20 packets of cigarettes a day.
Effects of air pollution:
Air pollution has adverse effects on living organisms and materials.
1] Effects on Human Health:
The human respiratory system has several mechanisms for protection from air pollution. The hairs and sticky mucus in the lining of the nose can trap bigger particles. Smaller particles can reach the tracheobronchial system and there get trapped in mucus. They are sent back to the throat by beating hair-like cilia from where they can remove by spitting or swallowing. Years of exposure to air pollutants (including cigarette smoke) adversely affect these natural defenses and can result in lung cancer, asthma, chronic bronchitis and emphysema (damage to air sacs leading to loss of lung elasticity and acute shortness of breath).
Suspended particulate can cause damage to lung tissues and diseases like asthma, bronchitis, and cancer especially when they bring with them cancer-causing or toxic pollutants attached on their surface. Sulfur dioxide (S02) causes constriction of respiratory passage and can cause bronchitis like conditions. In the presence of suspended particulate, S02 can form acid sulfate particles, which can go deep into the lungs and affect them severely.
Oxides of nitrogen especially NO2 can irritate the lungs and cause conditions like chronic bronchitis and emphysema. Carbon monoxide (CO) reaches the lungs and combines with hemoglobin of the blood to form carboxyhemoglobin. CO has an affinity for hemoglobin 210 times more than oxygen. Hemoglobin is, therefore, unable to transport oxygen to various parts of the body. This causes suffocation. Long exposure to CO may cause dizziness, unconsciousness and even death. Many other air pollutants like benzene (from unleaded petrol), formaldehyde and particulate like polychlorinated biphenyls (PCBs) toxic metals and dioxins (from burning of polythene) can cause mutations, reproductive problems or even cancer.
2] Effects on Plants:
Air pollutants affect plants by entering through stomata (leaf pores through which gases diffuse), destroy chlorophyll and affect photosynthesis. Pollutants also erode waxy coating of the leaves called a cuticle. Cuticle prevents excessive water loss -and damage from diseases, pests, drought, and frost. Damage to leaf structure causes necrosis (dead areas of the leaf), chlorosis (loss or reduction of chlorophyll causing yellowing of leaf) or epinasty (downward Curling of leaf) and abscission (dropping of leaves). Particulates deposited on leaves can form encrustations and plug the stomata. The damage can result in the death of the plant.
3] Effects on aquatic life:
Air pollutants mixing up with rain can cause high acidity (lower pH) in freshwater lakes. This affects-aquatic life especially fishes. Some of the freshwater lakes have experienced total fish death.
4] Effects on materials:
Because of their corrosiveness, particulate can cause damage to exposed surfaces. The presence of SO2 and moisture can accelerate the corrosion of metallic surfaces. SO2 can affect fabric, leather, paint, paper, marble, and limestone. Ozone in the atmosphere can cause cracking of rubber. Oxides of nitrogen can also cause fading of cotton and rayon fibers.
Control of air pollution:
Air pollution can minimize by the following simple methods:
- Siting of industries after proper Environmental Impact Assessment studies.
- Removing sulfur from coal (by washing or with the help of bacteria).
- Removing NOx during the combustion process.
- Using low sulfur coal in industries.
- Removing particulate from stack exhaust gases by employing electrostatic precipitators, bag-house filters, cyclone separators, scrubbers, etc.
- Vehicular pollution can check by regular tune-up of engines; replacement of more polluting old vehicles; installing catalytic converters; by the engine, modification to have fuel-efficient (lean) mixtures to reduce CO and hydrocarbon emissions; and slow and cooler burning of fuels to reduce NOx emission (Honda Technology).
- Using the mass transport system, bicycles, etc.
- Shifting to less polluting fuels (hydrogen gas).
- Using non-conventional sources of energy.
- Using biological filters and bio-scrubbers.
- Planting more trees.
The following items are commonly used as pollution control devices by industry or transportation devices. They can either destroy contaminants or remove them from an exhaust stream before it emits into the atmosphere.
1] Particulate Control:
Mechanical collectors (dust cyclones, multi-cyclones)- Cyclonic separation is a method of removing particulates from an air, gas or water stream, without the use of filters, through vortex separation. Rotational effects and gravity are used to separate mixtures of solids and fluids. A high speed rotating (air) flow establish within a cylindrical or conical container called a cyclone.
Air flows in a spiral pattern, beginning at the top (wide end) of the cyclone and ending at the bottom (narrow) end before exiting the cyclone in a straight stream through the center of the cyclone and out the top. Larger (denser) particles in the rotating stream have too much inertia to follow the tight curve of the stream and strike the outside wall, falling then to the bottom of the cyclone where they can remove.
In a conical system, as the rotating flow moves towards the narrow end of the cyclone the rotational radius of the stream reduces, separating smaller and smaller particles. The cyclone geometry, together with flow rate, defines the cut point of the cyclone. This is the size of the particle that will remove from the stream with 50% efficiency. Particles larger than the cut point will remove with greater efficiency and smaller particles with lower efficiency.
2] Electrostatic Precipitators:
An electrostatic precipitator (ESP), or electrostatic air cleaner is a particulate collection device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge.
Electrostatic precipitators are highly efficient filtration devices that minimally impede the flow of gases through the device, and can easily remove fine particulate matter such as dust and smoke from the air stream.
In contrast to wet scrubbers which apply energy directly to the flowing fluid medium, an ESP applies energy only to the particulate matter being collecting and therefore is very efficient in its consumption of energy (in the form of electricity).
3] Particulate Scrubbers:
The term wet scrubber describes a variety of devices that remove pollutants from a furnace flue gas or other gas streams. In a wet scrubber, the polluted gas stream is brought into contact with the scrubbing liquid, by spraying it with the liquid, by forcing it through a pool of liquid, or by some other contact method, to remove the pollutants. The design of wet scrubbers or any air pollution control device depends on the industrial process conditions and the nature of the air pollutants involved.
Inlet gas characteristics and dust properties (if particles are present) are of primary importance. Scrubbers can design to collect particulate matter and/or gaseous pollutants. Wet scrubbers remove dust particles by capturing them in liquid droplets. Wet scrubbers remove pollutant gases by dissolving or absorbing them into the liquid.
Any droplets that are in the scrubber inlet gas must separate from the outlet gas stream using another device referred to as a mist eliminator or entrainment separator (these terms are interchangeable).