Air pollution is the introduction of particulates, biological molecules, or other harmful materials into Earth’s atmosphere, causing diseases, death to humans, damage to other living organisms such as animals and food crops, or the natural or built environment. Air pollution may come from anthropogenic or natural sources.
The atmosphere is a complex natural gaseous system that is essential to support life on planet Earth. Stratospheric ozone depletion due to air pollution has been recognized as a threat to human health as well as to the Earth’s ecosystems.
Cause of Air Pollution
The various causes of air pollution are:
- Combustion of natural gas, petroleum, coal and wood in industries, automobiles, aircrafts, railways, thermal plants, agricultural burning, kitchens, etc. (soot, flyash, CO2, CO, nitrogen oxides, sulphur oxides).
- Metallurgical processing (mineral dust, fumes containing fluorides, sulphides and metallic pollutants like lead, chromium, nickel, beryllium, arsenic, vanadium, cadmium, zinc, mercury).
- Chemical industries including pesticides, fertilizers, fungicides.
- Processing industries like cotton textiles, wheat flour mills, asbestos.
- Welding, stone crushing, gem grinding.
An air pollutant is a substance in the air that can have adverse effects on humans and the ecosystem. The substance can be solid particles, liquid droplets, or gases. A pollutant can be of natural origin or man-made. Pollutants are classified as primary or secondary. Primary pollutants are usually produced from a process, such as ash from a volcanic eruption. Other examples include carbon monoxide gas from motor vehicle exhaust, or the sulfur dioxide released from factories. Secondary pollutants are not emitted directly. Rather, they form in the air when primary pollutants react or interact. Ground level ozone is a prominent example of a secondary pollutant. Some pollutants may be both primary and secondary: they are both emitted directly and formed from other primary pollutants.
A. Natural sources
The natural sources of air pollutants includes volcanic eruptions, forest fires, deflation of sands and dusts, storms, etc.
Pollutants from natural sources
Volcanic pollutants are produced as a result of volcanic activities. Examples: ashes, smokes, carbon dioxide, chlorine, sulfur, dust and other gases.
Land surface pollutants often get mixed with earth’s atmosphere. The dust, sand, soil particles, salt, etc. are the examples of land pollutants.
The cosmic particles and rays, comets, etc. are the natural sources of air pollution.
Green plants and vegetation that produces Volatile organic compounds (VOC) in large quantity are indirect pollutants.
B. Anthropogenic (Man-made sources)
Industries, automobiles, agriculture, power plants, domestic sources, etc. are the man-made or anthropogenic sources of air pollution. Major primary pollutants produced by human activity include:
Carbon monoxide (CO) – It accounts for 50% of the total atmospheric pollutants.CO is a colorless, odorless, toxic and non-irritating gas. It is a product by incomplete combustion of fuel such as natural gas, coal or wood. Vehicular exhaust is a major source of carbon monoxide. Carbon monoxide combines with haemoglobin of blood and impairs its oxygen carrying capacity. At higher concentration, carbon monoxide proves lethal.
Volatile organic compounds (VOC) – VOCs are a well-known outdoor air pollutant. They are categorized as either methane (CH4) or non-methane (NMVOCs). Methane is extremely an efficient greenhouse gas which contributes to enhance global warming. Other hydrocarbon VOCs are also significant greenhouse gases because of their role in creating ozone and prolonging the life of methane in the atmosphere. This effect varies depending on local air quality. The aromatic NMVOCs benzene, toluene and xylene are suspected carcinogens and may lead to leukemia with prolonged exposure.
Sulphur Oxides They occur mainly in the form of sulphur dioxide. It is produced in large quantity during smelting of metallic ores and burning of petroleum and coal in industries, thermal plants, home and motor vehicles. In the air, SO2 combines with water to form sulphurous acid (H2SO3) which is the cause of acid rain. It causes chlorosis and necrosis of vegetation. Sulphur dioxide, above 1 ppm, affects human beings. It causes irritation to eyes and injury to respiratory tract. It results in discolouration and deterioration of buildings, sculptures, painted surfaces, fabrics, paper, leather, etc.
Nitrogen Oxides They are produced naturally through biological and non-biological activities from nitrates, nitrites, electric storms, high energy radiations and solar flares. Human activity forms nitrogen oxides in combustion process of industries, automobiles, incinerators and nitrogen fertilizers. Nitrogen oxides act on unsaturated hydrocarbons to form peroxy-acyl nitrates or PAN. It gives rise to photochemical smog. They cause eye irritation, respiratory troubles, blood congestion and dilation of arteries.
Particulate Matter It is of two types—settleable and suspended. The smaller particles are able to remain suspended for long periods in the air. The important effects of particulate matter are.
- Dust and smoke particles cause irritation of the respiratory tract and produces bronchitis, asthma and lung diseases.
- Smog is a dark or opaque fog which is formed by the dust and smoke particles causing condensation of water vapours around them as well as attracting chemicals like SO2, H2S, NO2, etc. Smog harms plant life through glazing and necrosis besides reduced availability of light. In human beings and animals it produces respiratory troubles.
- Particulate matter suspended in air, scatters and partly absorbs light. In industrial and urban areas, sunlight is reduced to 1/3 in summer and 2/3 in winter.
- At a concentration above 150 g/100m3, cotton dust in ginning process produces pneumoconiosis or lung fibrosis called byssinosis. Lung fibrosis produced in other industries includes asbestosis (in asbestos industry), silicosis (stone grinders), siderosis (iron mill), coal miners’ pneumoconiosis, flour mill pneumoconiosis, etc.
Effects of air pollution
Air pollution can harm us when it accumulates in the air in high enough concentrations. People exposed to high enough levels of certain air pollutants may experience:
- Irritation of the eyes, nose, and throat
- Wheezing, coughing, chest tightness, and breathing difficulties
- Worsening of existing lung and heart problems, such as asthma
- Increased risk of heart attack
- In addition, long-term exposure to air pollution can cause cancer and damage to the immune, neurological, reproductive, and respiratory systems. In extreme cases, it can even cause death.
- Acid rain is precipitation containing harmful amounts of nitric and sulfuric acids. These acids are formed primarily by nitrogen oxides and sulfur oxides released into the atmosphere when fossil fuels are burned.
- Ozone depletion – Ozone is a gas that occurs both at ground-level and in the Earth’s upper atmosphere, known as the stratosphere. At ground level, ozone is a pollutant that can harm human health. In the stratosphere, however, ozone forms a layer that protects life on earth from the sun’s harmful ultraviolet (UV) rays. But this “good” ozone is gradually being destroyed by man-made chemicals referred to as ozone-depleting substances, including chlorofluorocarbons, hydrochlorofluorocarbons, and halons.
- Crop and forest damage – Air pollution can damage crops and trees in a variety of ways. Ground-level ozone can lead to reductions in agricultural crop and commercial forest yields, reduced growth and survivability of tree seedlings, increased plant susceptibility to disease, pests and other environmental stresses (such as harsh weather).
- Global climate change – The Earth’s atmosphere contains a delicate balance of naturally occurring gases that trap some of the sun’s heat near the Earth’s surface. This “greenhouse effect” keeps the Earth’s temperature stable. Unfortunately, evidence is mounting that humans have disturbed this natural balance by producing large amounts of some of these greenhouse gases, including carbon dioxide and methane
- Control of Air Pollution
- Industrial estates should be established at a distance from residential areas.
- Use of tall chimneys shall reduce the air pollution in the surroundings and compulsory use of filters and electrostatic precipitators in the chimneys.
- Removal of poisonous gases by passing the fumes through water tower scrubber or spray collector.
- Use of high temperature incinerators for reduction in particulate ash production.
- Development and employment of non-combustive sources of energy, e.g., nuclear power, geothermal power, solar power, tidal power, wind power, etc.
- Use of non-lead antiknock agents in gasoline.
- Attempt should be made to develop pollution free fuels for automobiles, e.g., alcohol, hydrogen, battery power. Automobiles should be fitted with exhaust emission controls.
- Industrial plants and refineries should be fitted with equipment for removal and recycling of wastes.