Air pollution refers to the presence of contaminants such as dust, smoke, mist, and odors in the atmosphere that are harmful to humans, plants, and animals. According to the Central Pollution Control Board (CPCB), air pollution occurs when one or more contaminants exist in concentrations that are harmful or likely to be harmful over time.
These pollutants may vary in physical and chemical properties, influencing their toxic potential and environmental impact.
Air pollutants can originate from both natural sources and human-made (anthropogenic) activities. Rapid industrialization, uncontrolled population growth, increasing vehicular traffic, and natural phenomena like volcanic eruptions or forest fires disrupt the balance of the atmosphere.
Include events and processes such as:
Natural sources often lie beyond human control, yet significantly impact global air quality. For example, volcanic eruptions release large volumes of ash and toxic gases into the atmosphere, drastically deteriorating air quality.
Anthropogenic sources include:
These activities emit pollutants such as carbon monoxide, carbon dioxide, oxides of nitrogen and sulphur, hydrocarbons, ozone, and other particulate matter.
Manufacturing units using nitric and sulphuric acids release vast amounts of oxides of nitrogen and sulphur. Other emissions include carbon dioxide from general industrial processes, chlorine from caustic soda plants, and carbon monoxide, hydrogen sulphide, and metal particulates from metallurgical operations. Specialized industries such as plastic, asbestos, and tobacco are also significant contributors.
Fossil fuels such as crude oil, coal, and natural gas are carbon-rich and widely used for energy production. Petroleum refining yields fuels and by-products like pesticides, plastics, and fertilizers, many of which release greenhouse gases.
During drilling and transportation, oil spills and emissions occur—especially from marine tankers and refinery leaks. Coal combustion releases sulphur dioxide, nitrogen oxides, and mercury, while natural gas emits methane, which is over 20 times more potent than carbon dioxide.
Mining involves blasting, digging, and transportation, all of which generate dust and pollute air. Destruction of topsoil and vegetation contributes to ecological damage. Contamination of nearby water bodies from mining waste is also a common consequence.
Coal-powered plants are traditional sources of energy but emit large quantities of CO₂, CO, and SO₂. Nuclear energy offers a cleaner alternative but requires high standards of maintenance and risk management.
Vehicles using petrol and diesel emit pollutants such as carbon monoxide and nitrogen oxides. Automobiles are among the largest contributors to urban air pollution.
Modern agriculture uses fertilizers, pesticides, insecticides, and fungicides which emit volatile chemicals into the air. Short-term exposure may lead to headaches, rashes, and eye irritation, while long-term effects include cancer, hormonal disruption, and birth defects.
You now know the various sources of air pollutants. Let us now explore the toxic elements, also referred to as air pollutants, which degrade air quality. These pollutants are categorized into three types:
Natural pollutants are substances that enter the atmosphere due to natural phenomena. These include:
Natural pollutants have existed since the Earth's formation and are considered less harmful due to nature’s ability to self-regulate them.
Primary pollutants are those that are emitted directly into the atmosphere through both natural processes and human activities. Examples include:
These pollutants are major contributors to acid rain through atmospheric chemical reactions.
These oxides contribute to acid rain and photochemical smog.
Secondary pollutants are not directly emitted but form when primary pollutants react chemically in the atmosphere. Examples include smog and ground-level ozone.
The chemical reactions behind these pollutants occur both day and night, especially due to human-induced combustion of fossil fuels and use of solvents in industry.
You have now gained an understanding of the sources and types of air pollutants, which stem from both natural and human-made activities. Air pollution is recognized as a major environmental risk to public health.
Air quality standards are frameworks developed by prominent organizations such as the United States Environmental Protection Agency (USEPA), Central Pollution Control Board (CPCB) of India, and the World Health Organization (WHO). These standards are designed to assess the concentration of air pollutants and their health effects, typically measured on a scale from 0 (healthy) to 500 (hazardously unhealthy).
Across global cities, the ambient air quality — referring to the outdoor air — is frequently assessed and categorized using a color-coded index that illustrates health impacts. This is demonstrated in Air Quality Index (AQI) systems like those presented in Table 9.1.
In India, the National Ambient Air Quality Standards (NAAQS) are prescribed by the CPCB under the authority of the Air (Prevention and Control of Pollution) Act, 1981. These standards apply nationwide to assess and regulate outdoor air quality.
In October 2014, India launched a simplified National Air Quality Index (AQI) to present data in an accessible format. This AQI evaluates eight major pollutants over short-term exposure periods (up to 24 hours):
Refer to Table 9.2 for specific pollutant limits across different environmental zones:
Source: CPCB, — India Air Quality Standards
Ambient air pollution refers to the condition of outdoor air in a given area. The main components of particulate matter (PM) include:
PM10 and PM2.5 are particles measuring 10 microns and 2.5 microns in diameter respectively. PM10 can reach the lungs, while PM2.5 penetrates deep enough to enter the bloodstream.
Air quality data is usually presented as daily or annual mean concentrations measured in micrograms per cubic meter (µg/m³).
You now have a solid understanding of air quality standards. It is equally crucial to recognize the effects of air pollution on all forms of life — from humans to plants and animals — as well as on materials essential to human welfare. These effects are broadly categorized into three major areas:
Air is a fundamental necessity for life, and when it becomes polluted, it severely impacts living organisms. Air quality alerts frequently appear in newspapers and television broadcasts, especially concerning urban environments.
Children and elderly people are particularly vulnerable, as polluted air irritates the eyes, nose, throat, and lungs. Toxic air does not only compromise the respiratory system but also disrupts overall bodily functions.
Toxic air pollutants affect animals in a manner similar to humans. Research shows that these pollutants contribute to birth defects, reproductive failures, and disease in wildlife. Aquatic ecosystems are also impacted as pollutants settle in sediments, bio-magnifying in top predators through the food chain.
Livestock around the world have been reported to suffer from poisoning due to pollutants such as fluorides and arsenic.
Beyond impacting human and animal health, air pollution also causes numerous environmental issues:
Several nations across the globe have made significant efforts to control air pollution through technological advancements. Despite progress, innovation in air pollution control has yet to achieve optimal results. Below are strategic measures suggested to manage and mitigate air pollution:
Setting up a centralized regulatory authority at the national level is vital to recommend and enforce air quality standards to protect public health. This includes:
Stringent regulations and penalties should be enforced on polluters, while also offering incentives to industries and individuals who emit lower levels of pollutants.
Using purified and high-quality petrol can significantly reduce sulphur and lead emissions. Modified and efficient automobile engines can also help minimize the emission of carbon monoxide and hydrocarbons.
Machines and engines should be optimized to use fuel more efficiently, thereby reducing the release of harmful pollutants.
Installing treatment plants to purify air pollutants and shifting toward alternative energy sources such as wind, water, and solar energy is critical. Promoting the use of solar-powered and battery-operated vehicles can reduce dependency on fossil fuels.
The following technologies can be used to manage industrial emissions effectively:
Strict monitoring of deforestation and promotion of afforestation are essential. Every citizen should adopt the motto: “Save and plant trees, save the homes of living organisms and the planet Earth.”
Trees absorb carbon dioxide for photosynthesis, acting as natural air purifiers. Broad-leaved trees are especially effective at trapping dust and gas particles on their foliage, functioning as particulate filters.
Environmental education should be integrated at all educational levels. Raising awareness from early childhood about the dangers of air pollution is the foundation of long-term environmental protection and responsibility.