Air Pollutants: What Are They and How Do They Affect Us?

Updated: Jul 28

We all know that air pollution is bad. It can lead to chronic health issues in humans and affects plants, animals and the surrounding environment, too.

What we might not know is where air pollution comes from, what it’s made of and how it really affects us. This article answers that, including the main types of air pollutants, both indoor and outdoor.

What is Air Pollution?

Air pollution is the contamination of indoor and outdoor air as a result of chemical, physical or biological substances that change the atmosphere, causing possible risks for humans. It can cause the air to become harmful to the health of humans and other living things or create damage to the climate or materials.

What Causes Air Pollution?

Many things can cause air pollution, but the most common causes include:

  • Fuel oils burning or evaporating

  • Natural gas burning

  • Coal burning

  • Chemical fumes

  • Wood-burning fires

  • Dust lifting/raising

  • Wildfires

  • Volcanic eruptions

  • Solvents’ use

  • Reactions in the atmosphere between compounds that are not pollutants on their own

What Pollutes the Air?

There are many different types of air pollutants. This article runs through the top eight outdoor air pollutants and the top seven indoor air pollutants in detail.

At a glance, these are:

Outdoor air pollutants

Indoor air pollutants

PM 10


PM 2.5





Biological pollutants

Carbon Monoxide




Sulphur dioxide



8 Types of Outdoor Air Pollution

1. PM 10

PM stands for ‘particulate matter’. PM 10 is up to 10 microns in size. To put this into context, the average width of a human hair is 70 microns and humans can’t see smaller than 50 microns with the naked eye.

This type of air pollution can predominantly be found on busy roads as vehicles and tyre brakes emit PM 10 when they’re used. Examples of PM 10 also include the smallest pollen, road erosion, and outdoor dust particles from people, houses and pavements.

The smaller the particle, the more harmful and difficult to avoid. PM 10 is considered respirable – able to be breathed in – and because of their size can settle deep into the

lungs with little chance of escape. This can cause numerous respiratory and cardiovascular health problems which can lead to premature death.

Health effects can include coughing, wheezing, asthma, bronchitis, high blood pressure, heart attacks, cancer, strokes and premature death.

2. PM 2.5

PM 2.5 is 20 times smaller than anything a human can see with the naked eye. They mainly come from combustion, such as vehicle exhausts and emissions, so any areas near an industrial complex or roads that see a lot of traffic will ordinarily have higher levels of PM 2.5. You may also breathe in PM 2.5 from chimney or vehicular soot or from heating particles such as those found under a car bonnet. Wood fires are also renowned for emitting PM 2.5 so step back at your next bonfire.

Because PM 2.5 is so small, it is easily breathable and is four times more likely to stay in your lungs once inhaled. They can cause the same respiratory and cardiovascular problems as PM 10 but are also small enough to seep into the blood, where particles can be carried around your body.

Health effects can include coughing, wheezing, asthma, bronchitis, high blood pressure, heart attacks, cancer, strokes and premature death.

3. Hydrocarbons

Hydrocarbons are a catch-all name for all organic compounds that are formed entirely from hydrogen and carbon. Examples include methane, benzene and polycyclic aromatic

hydrocarbons (PAHs). Able to take the form of gas, liquids and solids, hydrocarbons are most often burned for use as fuel.

The vast majority of hydrocarbons are found in petroleum, coal and natural gas. As such, anything that involves burning petrol, coal or natural gas outside will have an adverse effect on your health including vehicular emissions, camping stoves, petrol stations and smoking. They can eventually find their way into the soil and water sources like rivers and lakes.

Industrial factory emissions should also be avoided because of their burning of heavy metals; smelting, waste disposal, mining and industrial smoke all contribute to air pollution.

Hydrocarbons can cause a litany of problems if inhaled including low blood oxygen and shortness of breath. Because there are so many, each has its own properties with numerous cancers linked to prolonged exposure, as well as cardiovascular disease and poor foetal development.

4. Methane

Methane is an atmospheric pollutant that is much more efficient at trapping radiation than CO2 but with a shorter life. Its impact on climate change over 20 years is up to 86x greater than carbon dioxide.

It occurs naturally but has grown due to human activities in agriculture (livestock farming, rice cultivation, etc.) as well as from landfill, mining, burning of biomass, and fossil fuel production.

5. Carbon Monoxide (CO)

Often grouped in with hydrocarbons, carbon monoxide is a product of incomplete combustion. It is a colourless, odourless and tasteless flammable gas that is slightly less dense than air.

Roughly half the CO in Earth’s atmosphere comes from burning fossil fuels and biomass. It is most commonly caused by internal combustion engines – vehicle exhausts, lawn mowers, etc. – but is also found in incomplete combustion of wood, oil, etc.

Carbon monoxide is highly toxic and is the most common type of fatal air poisoning, usually due to using equipment indoors. Carbon monoxide poisoning rarely happens outdoors as CO is slightly less dense than air, though it can build up in caves and coal mines. CO replaces oxygen in the blood, which leads to flu-like symptoms if exposed for too long. If the CO level in the blood exceeds 50%, you could experience a seizure, coma or even death.

6. Ozone (O3)

You’ve probably heard of Ozone or O3; it’s a pale blue gas that’s formed from O2 by UV light and electrical discharges within the Earth’s atmosphere. Sunlight shines onto the hydrocarbons and nitrogen oxides, which react to form ozone.

Ozone that’s high in the atmosphere can protect us from dangerous UV radiations, which is why a hole in the ozone layer is a dangerous thing. But ozone that’s low in the atmosphere is dangerous for humans, animals and plants.

Ozone can be found in low concentrations across the world and is a powerful oxidant, often used in industrial and consumer applications, such as cleaners and disinfectants. Ozone helps kill bacteria on surfaces at restaurants and is used in washing fruit as well as bleaching materials. It is commonly used to disinfect water.

Levels are increasing in urban areas where the problem is made worse by denser populations and higher temperatures. Subject to numerous scientific research, it is harmful to humans at the levels currently found in cities.

It causes respiratory and cardiovascular problems, reproductive and development issues, and premature death, but is most harmful to those with preexisting conditions.

7. Sulphur Dioxide (SO2)

Sulphur Dioxide is a colourless gas that features a strong smell when burned. It is toxic and easily reacts to form harmful substances including sulphuric acid and sulphurous acid, as well as sulphate particles. These compounds also contribute to the acidification of land and water.

Sulphur dioxide is released naturally by volcanic eruptions but is more likely to appear in your local environment when burning fossil fuels contaminated with sulphuric compounds.

SO2 can make breathing difficult and harm the respiratory system. Exposure often results in coughing. High concentrations of SO2 can also lead sulphur oxides to react with other compounds, contributing to more PM 10 and PM 2.5 pollution. Sulphur dioxide can also harm trees and plants by decreasing growth and damaging foliage. SO2 is also a major contributor to acid rain, which harms the ecosystem and can be problematic for fish and other animals.

8. NOx

NOx is a term used in atmospheric chemistry to describe nitrogen oxides – primarily nitric oxide (NO) and nitrogen dioxide (NO2) – which are most relevant for air pollution. NOx gases are formed when nitrogen and oxygen react with one another. It is emitted by power plants and off-road equipment, e.g. a pneumatic drill, but its gases are also naturally produced by lightning.

Breathing air with a high concentration of NO2 can lead to respiratory problems. Longer exposure can lead to asthma and increased likelihood of other respiratory-related infections.

NO2 and other NOx particles can react with chemical pollutants in the air to form PM 2.5, PM 10 and ozone. NOx also contributes to nutrient pollution, an occurrence which involves too many nutrients running into water and acting like a fertiliser, causing excessive growth of algae.

7 Types of Indoor Air Pollution

1. Asbestos

Asbestos is a term that describes six naturally occurring silicate minerals, which form 90% of the Earth’s crust. Each of these silicate minerals are composed of long and thin fibrous crystals, the fibres of which are composed of microscopic fibrils, which can be easily released via abrasion.

Naturally occurring, asbestos can be found on numerous rock surfaces. It has been used for thousands of years as it is highly heat-resistant and an excellent electrical insulator. Because of its properties, most buildings built before 1980 are thought to contain asbestos.

Asbestos is so harmful to human health that using it for construction has been prohibited in the EU, UK, Australia, Japan, Hong Kong and New Zealand. Health problems can take decades to occur so it is uncertain how many deaths can be attributable to its use.

What is known is that inhalation of asbestos fibres can lead to long-term scarring and inflammation of the lungs, which can lead to wheezing. Long-term effects include lung cancer, mesothelioma, and pulmonary heart disease. Around 100,000 people a year are thought to die from asbestos-related diseases.

2. Formaldehyde

Formaldehyde (CH2O) is a naturally occurring organic compound. It has a pungent smell as a gas but is also colourless. Formaldehyde plays a key role in the industrial process, an important precursor to many other chemical compounds and materials.

Formaldehyde is an intermediate in the combustion of methane as well as other carbon compounds. It forms during forest fires, smoking and from vehicle emissions, often becoming a component of smog. It is often used in resins, adhesives and finishes, and can also be used as a fertiliser or pesticide, disinfectant and embalming agent.

As little as 30ml of ingested formaldehyde can kill an adult but it occurs naturally and is an essential part of the cellular metabolism in mammals and humans. Even so, long-term exposure via inhalation is harmful – formaldehyde is a carcinogen – and could occur from close proximity. Formaldehyde can be emitted from paints, varnishes and floor finishes. For most, exposure leads to irritation of the eyes, nose, throat and skin.

3. Volatile Organic Compounds (VOCs)

VOCs include a variety of chemicals and are emitted as gases from solids or liquids. Particularly problematic indoors, they can be up to ten times higher in concentration than outside. During certain activities (such as paint stripping), the indoors can be up to 1,000x more polluted than outdoors.

VOCs are so prevalent that it’s almost difficult to comprehend. VOCs can be emitted from: wall paint, paint stripper and other solvents, aerosol sprays, disinfectants, air fresheners, insect repellant, oil, petrol, wood stain, wood varnish, dry-cleaned clothing, pesticides, watercolour or chalk paints, building materials, furnishings, photocopiers, printers, permanent markers, correction fluid, glue, adhesive, and much more.

Health effects include: eye, nose and throat irritation, flu-like symptoms, damage to the liver, kidneys and central nervous system, and loss of coordination. Some VOCs are known to cause cancer. The health effects depend on toxicity, level of exposure and length of time exposed.

4. Biological Pollutants

Biological pollutants can occur from anything that is alive indoors. They can also emerge from any area that has standing water or is water-damaged. This includes viruses, animal fur, feathers, skin particles and pollen as well as dust mites, cockroaches, insect parts, animal droppings, and even saliva from a pet. Mould and mildew can also cause problems.

The majority of biological pollutants can be inhaled and are often noticed when allergic reactions occur. Long exposure can cause the onset of allergies and asthma in children and even healthy people. Common symptoms are difficulty breathing, itchy eyes and a runny nose. Tuberculosis, measles, influenza and Covid-19 are all biological pollutants and in the worst cases can cause death.

5. Radon (Rn)

Formed when uranium decays, Radon is a colourless, odourless and radioactive gas. There are small amounts of uranium in all rocks and soils, which explains its prevalence in the environment. Indoor areas are generally worse due to lower air pressure indoors.

The lowest floors in your home and workplace are the most likely source of radon exposure.

Any exposure to radon is a health risk and this risk often increases in winter. High exposure causes damage to living tissues and creates an increased risk of lung cancer. Radon-related lung cancer causes more deaths each year than accidents at work and drink-driving combined.

6. Lead

Lead is a heavy metal that is denser and softer than most other materials. As such, it is easily malleable and has a low melting point. Lead is easily extracted from natural rocks and has been used for thousands of years, from ancient Rome through to the Industrial Revolution.

Lead is often used in construction as well as in plumbing, batteries and ammunition. Although toxic, it is particularly useful in technology where it can be used as solder and fusible alloys, and has also been used for paint, weights, leaded fuel and pewter.

When inhaled, lead is distributed via blood and accumulates in the bones. Depending on the level of exposure, it can cause cardiovascular problems as well as affecting the nervous system, kidneys, immune system, reproductive and developmental systems, leading to behavioural problems and learning difficulties in young children.

7. Pesticides

Pesticides are a catch-all term for substances that control pests. They are most often used to protect plants from weeds, insects and fungi.

The most common pesticides are man made and can be bought for use in your garden. They tend to be chemicals or biological agents (such as viruses or bacteria), which most often deter, incapacitate or kill pests including birds, molluscs, fish and microbes, to name just a few.

Health effects can often be delayed but they have been linked to non Hodgkin's lymphoma and leukaemia as well as to neurological disorders, birth defects and foetal death. Acute health problems include dizziness, headaches and nausea, as well as skin and eye irritation.

It has been estimated that around 385 million cases of unintentional acute pesticide poisoning occur annually worldwide with around 11,000 deaths. Pyrethrins, a form of insecticide, can also be deadly if breathed in. Other long term effects include cancer and an increased risk of diabetes.

Is There a Solution?

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