What are air pollutants and why do they matter in today’s world? Air pollutants are harmful substances released into the atmosphere that degrade air quality and threaten human health and the environment. Understanding the types and sources of air pollutants helps identify whether they originate as gases, particulates, or chemical compounds. The sources of air pollution include industries, vehicles, power plants, construction activities, and natural events such as wildfires and dust storms. These emissions lead to serious effects of air pollution, including respiratory diseases, climate change, and ecosystem damage. Engineers and scientists also classify pollutants as primary and secondary air pollutants, based on how they form in the atmosphere. Studying air pollution causes and effects is essential for developing control strategies, improving air quality, and protecting public health and the environment.
Most of the times you can’t see it or smell it, but air pollutants kill. As the level of air pollutants in our atmosphere are rising at an alarming rate we must be aware of them. In the previous blogs, we had described the causes and effects of air pollution. Today let’s dive deep into various air pollutants.
Let’s get started.
Table of contents
What are Air Pollutants ?
Air pollutants are harmful substances present in the atmosphere that degrade air quality and pose risks to human health, animals, plants, and the environment. These substances enter the air from natural and human-made activities and exist in solid, liquid, or gaseous forms. Air pollutants are broadly classified into primary pollutants and secondary pollutants.
Primary pollutants, such as dust, smoke, carbon monoxide, sulphur dioxide, and ammonia, enter the atmosphere directly from sources like industries, vehicles, and combustion processes. In contrast, secondary pollutants form within the atmosphere when primary pollutants react with sunlight, oxygen, or moisture. Common examples include ozone, sulphur trioxide, peroxyacetyl nitrate (PAN), and ketones. Understanding air pollutants and their formation is essential for analysing air pollution sources, impacts, and control measures.
Types of air pollutants
The types of air pollutants are commonly classified by the Environmental Protection Agency into three major categories based on their impact on health, environment, and climate.
The Environmental Protection Agency regulates three types of air pollutants:
- Criteria air pollutants
- Air Toxics
- Greenhouse Gases
Criteria Air Pollutants
Criteria air pollutants are major types of air pollutants regulated due to their widespread presence and strong impact on health and the environment. They include particulate matter (PM), ozone (photochemical oxidants), carbon monoxide, sulphur oxides, nitrogen oxides, and lead. These pollutants cause respiratory and cardiovascular diseases, reduce air visibility, damage ecosystems, and deteriorate buildings and infrastructure.
Air Toxics
Air toxics are hazardous types of air pollutants that include more than 180 substances. These consist of volatile organic compounds (VOCs), organic chemicals, metals and metal compounds, solvents, mercury, arsenic, asbestos, and benzene. Even in small concentrations, air toxics can cause serious health effects such as cancer, organ damage, and long-term environmental contamination.
Greenhouse Gases
Greenhouse gases are climate-related types of air pollution that include carbon dioxide, methane, chlorofluorocarbons (CFCs), and ozone. These gases trap heat in the atmosphere, intensify the greenhouse effect, and contribute to global warming and climate change, indirectly affecting air quality and human health.
Criteria air pollutants
Criteria Air pollutants include Particulate matter (PM), photochemical oxidants (e.g., ozone), carbon monoxide, sulphur oxide, nitrogen oxide, and lead. They can have a significant impact on public health and wellbeing, the atmosphere and environment, and neighbouring structures.
Air Toxics
The term “air toxics” consists of a list of over 180 air pollutants such as organic chemicals, volatile organic compounds (VOCs), metals, metal compounds, solvents, mercury, arsenic, asbestos, and benzene etc. Even when existent in trace amounts and emitted by fewer sources than criteria pollutants, they have harmful health and environmental impacts.
Greenhouse Gases
Greenhouse gases (GHGs) are gases such as carbon dioxide, chlorofluorocarbons (CFCs), methane, and ozone. They can harm human health. In addition, they contribute to the acceleration of the greenhouse effect on Earth and the resulting impact on global climate.
Major Air Pollutants Sources and Effects
The sources of air pollutants can be natural or anthropogenic. Check out our previous blog Air Pollution Causes – A Comprehensive Guide for detailed information on various sources of air pollutants. Let me describe each one in detail.
Nitrogen Oxides – Air pollutant Source
Nitrogen oxides (NOₓ), especially nitrogen dioxide (NO₂), are harmful air pollutants mainly released during high-temperature combustion processes such as vehicle engines, power plants, and industrial furnaces. Natural sources like electric discharge during thunderstorms also generate small amounts of nitrogen oxides. Nitrogen dioxide is a reddish-brown, poisonous gas with a sharp, irritating odour and often appears as a brown haze over urban areas or as plumes downwind of emission sources. Elevated NO₂ levels irritate and inflame the lining of the respiratory tract. Prolonged exposure can worsen asthma and trigger COPD flare-ups, causing coughing, wheezing, chest tightness, and difficulty in breathing. Nitrogen oxides also contribute to smog formation and secondary air pollutant generation.
Carbon Monoxide
Carbon monoxide (CO) is a highly poisonous air pollutant that is colourless, odourless, and tasteless, making it especially dangerous. It forms mainly from incomplete combustion of fuels in vehicles, generators, industrial processes, and heating systems. Carbon monoxide contributes to smog formation and deteriorates urban air quality. When inhaled, CO reacts with haemoglobin in the blood to form carboxyhaemoglobin, which has nearly 200 times higher affinity for haemoglobin than oxygen. This reaction significantly reduces the blood’s oxygen-carrying capacity, depriving body tissues of oxygen. At carboxyhaemoglobin saturation levels of around 20%, CO can impair heart function and cause tissue damage. Prolonged or high exposure is linked to serious respiratory disorders and adverse environmental impacts.
Sulphur Oxides
Sulphur oxides (SOₓ) are harmful air pollutants primarily produced during the combustion of sulphur-containing fuels such as coal and petroleum. The burning of these fuels releases sulphur dioxide (SO₂) into the atmosphere. Further oxidation of SO₂, often in the presence of catalysts like nitrogen dioxide (NO₂), forms sulphuric acid (H₂SO₄), which leads to acid rain. Major sources of sulphur oxides include power plants, oil refineries, chemical industries, paper mills, and fuel manufacturing facilities. Exposure to sulphur dioxide can aggravate respiratory conditions such as asthma and emphysema and cause breathing difficulties. SO₂ also irritates the eyes, nose, and throat. In addition, sulphur oxides damage crops and forests, corrode buildings, and reduce visibility over long distances.
Volatile Organic Compounds – Air pollutant Source
Volatile Organic Compounds (VOCs) are a major group of air pollutants characterised by high vapour pressure and low water solubility, which allow them to evaporate easily into the atmosphere. Industries widely use and generate VOCs during the manufacturing of paints, pharmaceuticals, adhesives, fuels, and refrigerants. Common VOCs include industrial solvents such as trichloroethylene, fuel oxygenates like methyl tert-butyl ether (MTBE), and chlorination by-products such as chloroform. Aromatic non-methane VOCs, including benzene, toluene, and xylene, are of particular concern due to their toxic and carcinogenic nature. Long-term exposure to these compounds can cause serious health effects, including leukaemia and other blood disorders, and they also contribute to smog formation and poor air quality.
Carbon Dioxide
Carbon dioxide (CO₂) is the most significant greenhouse gas air pollutant released through human activities. Major sources of carbon dioxide emissions include fossil fuel combustion, industrial processes, power generation, transportation, and wildfires. CO₂ traps outgoing solar radiation reflected from the Earth’s surface, leading to a rise in global average temperatures. Due to its strong contribution to the greenhouse effect and climate change, carbon dioxide is often regarded as a major climate pollutant. In the atmosphere, CO₂ also reacts with water vapour to form weak carbonic acid, contributing to atmospheric acidification and mildly acidic rainfall. Elevated carbon dioxide levels play a central role in global warming, climate instability, and long-term environmental change.
Particulate Matter – Air pollutant Source
Fine particles, also known as atmospheric particulate matter, are microscopic solid or liquid particles suspended in a gas. Volcanoes, dust storms, forest and grassland fires, and sea spray are all sources of particulate matter. Particulate air pollution comprises the following:
PM10: inhalable particles with a diameter of 10 micrometres or less.
Can you imagine how small is 2.5 micrometre? Consider a single hair on your head. The average human hair is 70 micrometres in diameter, which is 30 times the size of the smallest microscopic particle. I hope this makes it clear how they penetrate deep into our lungs.
Aerosols
Aerosols are produced by human activities such as the combustion of fossil fuels in automobiles, power plants, and numerous industrial processes. Anthropogenic aerosols, or those produced by human activity, currently make up around 10% of our atmosphere. Increased fine particle levels in the air have been related to health risks such as heart disease.
Chlorofluorocarbons – Air pollutant Source
- CFCs are gases emitted by air conditioners, freezers, aerosol sprays, and other similar devices.
- CFCs reach the stratosphere after being released into the atmosphere.
- They interact with other gases here, causing harm to the ozone layer.
- This allows UV radiation to reach the earth’s surface, which are hazardous.
- This can result in skin cancer, eye problems etc.
- As a result, they are currently restricted from usage in products.
Ammonia
Ammonia is a gas that is emitted primarily by agricultural waste. As a precursor to foodstuffs and fertilisers, it contributes considerably to the nutritional demands of terrestrial species. It is both corrosive and toxic, despite its widespread use. Ammonia combines with nitrogen and sulphur oxides in the atmosphere to generate secondary pollutants.
Ozone – Air pollutant Source
- Carbon monoxide (CO), methane (CH4), or other volatile organic compounds (VOCs) are oxidised in the presence of nitrogen oxides (NOx) and sunlight to form ozone.
- As a result, ozone is most abundant in the summer.
- Ground-level ozone is a primary component of photochemical smog.
- It is a significant health hazard connected to breathing issues, asthma, deterioration of lung function, and respiratory disorders.
- People with asthma may experience more frequent asthma attacks as a result of ozone exposure, as well as sore throats, coughing, and breathing difficulties.
- It could potentially result in premature death. Plants and crops can be harmed by ozone.
Lead
Lead is a neurotoxin and one of the main sources of Air pollutants. It was earlier used in petrol as an antiknocking agent. The fine particles emitted through automobile exhausts reaches the lungs and settles down there. At higher levels in the blood, it interferes with haemoglobin production. This results in oxygen starvation and anaemia. Higher levels lead to behavioural disorders.
Cadmium
Cigarette smoking is the main contributor to cadmium in the atmosphere. It can cause hypertension, cardiovascular diseases, kidney and liver damage.
Nickel
Finely divided nickel can react with carbon monoxide and forms Nickel Carbonyl. It is also formed in cigarette smoke. When it reaches our lungs it breaks down and deposits finely divided nickel inside our lungs. This is the main cause of lung cancer.
Mercury
Mercury is one of the air pollutants that enters the aquatic systems and soil from the atmosphere through acid rain. The adverse effects of mercury poisoning include chromosomal aberrations, neurological damage and even death. It can damage the cerebellum and cortex of brain by penetrating the membranes separating bloodstream from the brain.
So, we had taken a quick trip understanding all the major air pollutants. In case of any doubts, feel free to ask in the comments.
Key Takeaways
- Air pollutants are harmful substances that degrade air quality and threaten public health and the environment.
- They exist in solid, liquid, or gaseous forms and can be classified as primary or secondary pollutants.
- Major types include criteria air pollutants, air toxics, and greenhouse gases, each with specific sources and effects.
- Common pollutants like nitrogen oxides, carbon monoxide, and sulphur oxides lead to serious health and environmental impacts.
- Understanding what are air pollutants is essential for developing effective control strategies and improving air quality.
Conclusion
Understanding what are air pollutants is essential for addressing today’s environmental and health challenges. Air pollutants include harmful substances released into the atmosphere that degrade air quality and threaten living organisms. The classification of air pollutants helps group them into different categories based on their origin, behaviour, and impact. Common types of air pollutants include gases, particulates, and toxic compounds emitted from natural and human activities. Scientists further divide them into primary and secondary air pollutants, depending on whether they are released directly or formed through atmospheric reactions. Typical examples of air pollutants include nitrogen oxides, carbon monoxide, sulphur oxides, volatile organic compounds, and carbon dioxide. A clear understanding of air pollutants and their classification forms the foundation for developing effective control strategies, improving air quality, and protecting public health and the environment.
