What’s Really in the Air We Breathe (Understanding the Makeup of Our Indoor Air)

Interested in learning about the quality of the air inside your home?

Maybe you’ve heard about the effects that poor air quality can have and want to learn more. Or maybe you’re experiencing some of these effects first hand!

If that sounds like you, you’re in the right place.

  • The different types of indoor air pollutants
  • What causes indoor contamination
  • The health impact of poor air quality
  • The role of indoor air monitoring and purification
proHVACinfo | What's Really In the Air We Breathe

The air we breathe is non-negotiable.

It isn’t something we can choose to avoid or change up to suit our needs, we are reliant on the air around us to breathe and that includes whatever contaminants and pollutants which it may carry.

Our air is made up of approximately 21% oxygen, the good stuff we really need, and the rest is a combination of different gases including nitrogen, argon, methane, and carbon dioxide as well as many other particles which aren’t great for our health.

The World Health Organization estimates as many as 7 million deaths every year are linked to the effects of air pollution, making it the world’s biggest environmental killer.

Pollutants are present both indoors and outdoors and here we’re looking at the makeup of our indoor air, the contaminants we breathe in every day and what we can do about it.

Issues with Indoor Air

When we think about pollution and contaminated air, we usually imagine a busy highway or smoke-filled metropolis.

We don’t think about our homes, offices and workplaces.

However, research carried out by New York’s Alfred P. Sloan Foundation and their Chemistry of Indoor Environments program revealed some shocking statistics.

Speaking on behalf of the program, Professor Allen Goldstein explains: “The vast majority of organic chemicals that we could measure in air were substantially higher indoors than outdoors.”

Looking further into the research, they found 50% of around 200 detected chemicals were about 10 times higher indoors than outdoors, with 80% showing concentrations at least twice as high.

This shows that being indoors and theoretically “away” from the pollution, car fumes and chemicals, may not be as safe as we think.

Let’s look more closely at the different contaminants in our indoor air and the air we breathe daily at work and at home.

Visible Indoor Air Contaminants

The contaminants in our air can be loosely split into two categories: visible and invisible contaminants.

Visible air contaminants can be seen by the naked eye and this is most clear when sunlight or artificial light catches the contaminants as they travel through the air. Common visible indoor air contaminants include:


Research carried out in Germany shows that the average person inhales over two tablespoons of particulates every single day and this includes a significant amount of dust.

Dust irritates the respiratory system as when it enters the body the particles land on the tracheal and bronchial surfaces.


Dirt, which can include soils, human contaminants, animal contaminants and other waste quickly builds up, even if you have a dedicated cleaning schedule.

People walk dirt into the home or office regularly and smaller particles can quickly enter the air and be breathed in.


Pollen and other visible antigens can easily enter the airstream via open windows, doors and ventilation systems. People with allergies and respiratory conditions may experience abnormally vigorous immune responses to the allergens too.

Human Skin

The human skin is a fascinating organ, but it also sheds regularly without us even noticing and these skin cells are light enough to remain suspended within the air as well as falling to the ground.

Dead human skin is one of the most prevalent visible contaminants you can see when spotting small particles floating through the air and yes, a lot of it is inhaled too.

Invisible Indoor Air Contaminants

Those small particles you can actually see in the air account for about 10% of its overall makeup.

The remainder are far too small to see, which makes them much easier to inhale.

There are a wide range of different biological particles entering our bodies through the air every day and below we’re looking at each in turn.


Bacteria are single-cell organisms which reproduce either outside or within the human body.

Bacteria in the air can lead to a wide range of different and dangerous infections. Bacteria can cause anything from ear infections to strep throat, tonsillitis and pneumonia.


While fungi aren’t something we’d expect to find in the air as they tend to grow in the ground, the tiniest fungi can be found in many air supplies.

Fungi are a range of different multi-celled plant organisms which grow easily in damp, warm places such as furnaces and under floors.

They can cause uncomfortable rashes and skin irritation.


Mold spores spread very quickly once they enter any environment and can be extremely damaging to human health.

They are a common component of dust in the air, but they need to be removed as quickly as possible to avoid spread and the respiratory irritation they can cause.


Viruses need a human body to grow and develop and once in an air supply will quickly enter the body and get to work.

They don’t survive for long outside of the human body and to effectively spread, they tend to be airborne and can be extremely damaging to health.

Common viruses can cause measles, flu, chickenpox and many other diseases.


VOCs or volatile organic compounds make up thousands of organic chemicals found in gases at room temperature.

They can occur naturally or can be man-made.

A large number of VOCs are emitted into the indoor air from building materials, cleaning compounds, office equipment, personal care products, pesticides and the activities of the occupants of a building.

The American Lung Association emphasizes how damaging VOCs can be to health as they can cause difficulty breathing, nausea and even cause damage to the central nervous system.

What Causes Indoor Air Contamination?

Indoor pollution sources which release particles or gases are the primary issue for indoor air quality issues.

Inadequate ventilation can also lead to higher indoor pollutant levels as outdoor air is not able to dilute emissions from sources of pollution from indoors.

High temperatures and humidity levels can also increase concentrations of some particles in the air.

Key sources of indoor air pollution include:

  • Oil, gas and kerosene
  • Coal
  • Wood
  • Tobacco products
  • Household cleaning, maintenance, and personal care products
  • Building materials, from asbestos-containing insulation to damp carpet and deteriorating fixtures and fittings
  • Central heating and cooling systems
  • Outdoor sources including outdoor air pollution, pesticides and radon

Some of these sources release pollutants continuously while others may emit higher levels at certain times, such as cooking equipment in use.

Poor ventilation can be a key issue for some homes and businesses as pollutants have the chance to accumulate to levels which can be harmful to health.

It is also important to remember climate and weather conditions can impact on indoor air quality.

Weather may influence whether windows are opened or closed, limiting how much air can be circulated and certain climatic conditions can lead to higher levels of indoor moisture, mold growth and condensation, which can all become dangerous if not controlled properly with ventilation and air conditioning.

How Outdoor Air Enters our Buildings

Outdoor air can enter and leave a building in a range of ways including:

  • Infiltration – outdoor air flows into buildings through openings, joints, and cracks in walls, floors, and ceilings, and around windows and doors.
  • Natural ventilation – as air moves between opened windows and doors
  • Mechanical ventilation – ventilation through the use of devices such as outdoor-vented fans and air-handling systems

The rate at which outdoor air replaces the air indoors is known as the air exchange rate. When the air exchange rate is low, due to a lack of the three methods mentioned above, then the level of pollutants in any indoor space is at risk of increasing and becoming a hazard to the health of all occupants of the building.

What about Outdoor Pollutants?

As we’ve already discussed, indoor pollutants are significantly higher than those outdoors.

The Environmental Protection Agency reports that the concentration of some pollutants indoors is as much as 5 times higher than typical outdoor concentrations and with Americans spending 90% of their time indoors, the risks are significantly higher.

Pollutants outside can easily disperse into the atmosphere and while there are high levels of pollution around the world, especially in urban areas, they are not as concentrated as indoors so the risk to our health is not as significant.

Focusing on minimizing the spread of pollutants indoors is essential to help bring down the health risks associated with inhaling high levels of VOCs and other biological components such as viruses and bacteria.

The Health Impact of Breathing Poor Quality Indoor Air

Dirty and unclean air, packed full of pollutants and contaminants is not good for our health on any level.

Mild irritations may be issues such as headaches, congestion, nausea and irritation, but the damage being caused may become more significant.

Research by Ambius found 1 in 2 office workers in the US felt a lack of focus due to poor air quality and 40% had actually taken sick leave due to issues relating to the air quality at work. Improving air quality at work is something employers should be taking very seriously to help cut down on sick days and give their workforce a safer and cleaner place to work.

The health issues that can arise from poor air quality are more far reaching than many people realize.

Poor air quality has been linked to lung and heart problems in many research studies and can be connected to serious issues such as emphysema, respiratory infection and even cancer.

The impact on pregnant women is also particularly pronounced and it can even lead to birth defects.

Research at The Ohio State University Medical Center has also found a connection between air quality and heart disease with section director of vascular medicine Sanjay Rajagopalan explaining: “Recent observational studies in humans suggest that within hours to days following exposure, blood pressure increases,” and this in turn puts pressure on the heart and cardiovascular system.

Air pollution poses a significant risk to health in general and is particularly worrying for people who already live with a chronic condition.

It’s known to particularly exacerbate allergies but also conditions such as asthma, diabetes, and chronic obstructive pulmonary disease (COPD).

Children and elderly people also fall into that vulnerable group which puts them at higher risk of illness if exposed to polluted indoor air.

The Role of Air Purification and Cleansing

The EPA provides a wide range of guidebooks and recommendations to help us deal with indoor air pollution in specific spaces and environments.

They have dedicated advice and guidelines for air quality in offices and look to support employees as well as management in taking the right steps to avoid any health issues due to internal air quality.

EPA also highlight the importance of filtration and ventilation in managing indoor air quality.

The most effective way of improving indoor air quality is to reduce and remove the source of pollutants as well as ventilating spaces appropriately with clean outdoor air.

Research discussed by EPA shows that filtration can be a suitable alternative to control and manage ventilation in some spaces as there isn’t always the structural capabilities to ensure the right levels of ventilation.

Portable air cleaning systems, purification systems for mold and the right filtration can make a significant difference.

Businesses and homeowners can look to upgrade their air filter within the furnace, central heating system or HVAC system to help improve air quality.

It is also important to remember regular maintenance and cleaning of these systems to ensure particles are not able to build up and become a significant health hazard.

Understanding the molecular makeup of the air we breathe can help us to understand the importance of keeping it clean.

Investing in the right systems and filtration is vital for ensuring our health and protecting against the potential damage of indoor air pollution.

Stephen Marks

Stephen Marks

Stephen is an HVAC and home-repair enthusiast. He's here to answer any of your questions about HVAC!

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Stephen Marks

Stephen Marks

Stephen is an HVAC and home-repair enthusiast. He's here to answer any of your questions about HVAC!

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