Indoor air pollutants: What’s in the air we breathe?

Indoor air is often between two and five times as polluted as outdoor air – it can even be as much as 100 times worse.1 How does this happen?

Outdoor air pollutants find their way indoors and become trapped when there is not proper ventilation. There are also sources of indoor air pollutants found within buildings, such as off-gassing from building materials or the growth of mold spores. Studies suggest that Americans spend around 93 percent of their time in enclosed buildings and cars, while Europeans spend 90 percent of their time indoors, indicating the severity of indoor air pollutants as a health concern.2,3

Learn about the specifics of pollutants andthe best air purifying technology for each.

There are two distinct types of indoor air pollutants that can be dangerous to breathe: particles and gases. Particles that could be in your indoor air include:

  • dust
  • mold spores
  • dust mites
  • pet dander
  • diesel soot

Examples of gas pollutants include:

Some indoor air pollutants contain both particles and gases, such as wildfire smoke and tobacco smoke.

Particles (particulate matter)

Airborne particles (also referred to as particulate matter or PM) include particles that are “aerosolized,” or light enough to be carried in the air. Most airborne particles are so small that they are invisible to the naked eye. Airborne particles are categorized into three sizes: coarse, fine and ultrafine.

Coarse particles (PM10)

Coarse particles, or PM10, are airborne particles ranging between 2.5 and 10 microns in diameter. For comparison, the diameter of a single human hair ranges from 17 to 181 microns. Coarse particles represent less than 1% of all airborne particles and cause irritation to the eyes, nose, and throat.

Examples of coarse particles include:4

Fine particles (PM2.5)

Fine particles are smaller than 2.5 microns in diameter. Fine particles are sometimesreferred to as PM2.5 and represent about 9% of all airborne particles.

PM2.5 has been linked to increasing the potential for heart attacks.

The small size of PM2.5 gives it the potential to lodge into lung tissue – triggering respiratory illnesses such as asthma, bronchitis, and emphysema. PM2.5 has also been linked to increasing the potential for cardiovascular problems such as arrhythmic heartbeats, and heart attacks.

Common sources of PM2.5 include:5,6

  • pet dander
  • soil
  • dust mites
  • household dust
  • bacteria (including Legionella, the bacterium responsible for Legionnaires’ disease)
  • vehicle exhaust and other combustion emissions
  • construction and demolition

Ultrafine particles (UFPs)

Ultrafine particles (UFPs) are smaller than 0.1 microns in diameter. About 90% of all airborne particles are this size.7 UFPs are not only the most numerous of airborne particles but also the most dangerous to your health.

UFPs are not only the most numerous of airborne particles but also the most dangerous to your health.

The tiny size of ultrafine particles enables them to be easily inhaled, deposited into the lungs and absorbed directly into the bloodstream. From there, they travel with your bloodstream to all vital organs, including your brain.

Common sources of dangerous ultrafine particles include:8,9

  • vehicle exhaust (especially diesel)
  • wildfire smoke
  • tobacco smoke
  • soot (carbon-based substance resulting from the incomplete combustion of hydrocarbons, such as the burning of wood and coal; other sources include oil refineries and other industrial plants)
  • viruses


Gaseous pollutants are gases produced by combustion and a number of off-gassing sources, such as:10

  • paints
  • varnishes
  • cleaning products
  • pressed-wood furniture
  • new carpets

Odors are generally gases. Below are the primary gases comprising dangerous indoor air pollutants.

Ozone (O3)

Ozone is a naturally occurring compound that plays a vital role in blocking out harmful ultraviolet light from the sun. At the ground level, ozone is toxic.

While other pollutants are emitted directly into the air by various sources, ozone is created by sunlight acting on nitrogen oxides (NO) and volatile organic compounds (VOCs) in the air.11

At the ground level, ozone is toxic.

Ozone is the primary component of smog. Ozone can also react with other chemicals, including some fragrances that give pine or citrus scents, to produce dangerous volatile organic compounds such as formaldehyde.

Short-term exposure to even low concentrations of ozone significantly reduces lung function, often causing respiratory inflammation. Other symptoms can include:12

  • chest pain
  • lung and throat irritation
  • coughing
  • wheezing
  • breathing difficulty during exercise

Long-term exposure may cause asthma and can result in serious and permanent structural damage to the lungs.

Nitrogen Dioxide (NO2)

Nitrogen dioxide is a harsh-smelling gas that can cause breathing problems. Nitrogen dioxide is a precursor for ozone and particulate matter. It is formed during thunderstorms and from combustion processes, most commonly from vehicle exhaust.13

Indoor sources of nitrogen dioxide include unvented heaters and gas stoves.14 Nitrogen dioxide can cause irritated lungs and lowered resistance to respiratory infections.

Carbon Monoxide (CO)

Carbon monoxide is typically formed from combustion processes, such as the burning of fuels like wood, oil, coal, charcoal, natural gas, and propane.

Indoors, common sources of carbon monoxide include:15,16

  • unvented kerosene and gas heaters
  • leaking chimneys and fireplaces
  • back-drafting from furnaces and water heaters

When combustion appliances inside a home are not correctly adjusted, levels of carbon monoxide can soar. It is also released outdoors by combustion engines in cars, trucks and other vehicles.

When combustion appliances inside a home are not correctly adjusted, levels of carbon monoxide can soar.

Short-term effects are similar to that of oxygen deprivation:17

  • headaches
  • dizziness
  • fatigue
  • heart palpitations
  • nausea
  • confusion
  • visual disturbance
  • muscle twitches

Exposure to high levels of carbon monoxide is dangerous because it prevents oxygen uptake in the blood, causing a lack of oxygen supply to the heart.

Sulfur Dioxide (SO2)

The prevalence of sulfur dioxide is primarily man-made.18 It is formed when energy sources containing sulfur, like coal and oil, are burned in industrial processes. It can also result from fuel combustion in vehicles.

The prevalence of sulfur dioxide is almost entirely man-made.

Sulfur dioxide is commonly responsible for acid rain and low visibility. When inhaled, sulfur dioxide can cause shortness of breath and chest pain. In the long term, it can cause acute respiratory illness and permanent changes to the lungs.


Radon is a naturally forming, radioactive, colorless, odorless and tasteless gas. It is found in almost all soil and can enter a home through cracks in the floor or walls of the basement or foundation.

Radon exposure is the second leading cause of lung cancer among nonsmokers in the U.S.

Radon is produced by a natural process as uranium breaks down into radium and then into radon gas. It then breaks down into solid radioactive elements known as “radon progeny” that attach to airborne particles and can be inhaled. Radon exposure is the second leading cause of lung cancer among nonsmokers in the U.S.19

Volatile organic compounds (VOCs)

VOCs are also an example of gaseous indoor air pollutants emitted by solids or liquids. Common indoor sources of VOCs include:20

  • paints
  • paint thinners
  • adhesives
  • furniture
  • carpeting
  • household chemicals
  • caulking
  • ceiling tiles

Some VOCs can cause:21

  • headaches
  • eye, nose, and throat irritation
  • respiratory tract irritation
  • breathing problems

VOCs have also been linked to cancer.22

Among the most dangerous indoor VOCs and their common sources include:

  • toluene (Methylbenzene) from paint thinners.
  • xylene (para and/or meta), comes from printed materials, rubber and leather.
  • benzene,a known carcinogen, from tobacco smoke, stored fuels, and vehicle exhaust from attached garages


Formaldehyde is a naturally occurring VOC found in plants, fruits, vegetables, animals, and humans. Formaldehyde is naturally present in indoor and outdoor air at a very low level.

A synthetic form of formaldehyde is manufactured as a chemical used as an adhesive in cabinetry and flooring, among other products. After manufacturing, products containing formaldehyde continue to emit the colorless (but not odorless) gas into the air. Off-gassing – the release into the air of a gas that was dissolved, trapped, frozen or absorbed in a material – is not normally a problem when products are used outdoors.

But indoors, the emitted gas may build up quickly. Off-gassing increases when the temperature rises above 72 degrees Fahrenheit (22.2 Celsius) and/or humidity levels climb above 50 percent. Although levels of formaldehyde emissions decrease over time, significant off-gassing may continue for months and even years.

The potential dangers of exposure to formaldehyde include both short- and long-term effects. When formaldehyde is present in the air at levels exceeding 0.1 parts per million (PPM), you may experience:23

  • a burning sensation in the eyes, nose, and throat
  • coughing
  • wheezing
  • nausea
  • skin irritation

Perchloroethylene (“perc”)

Perchloroethylene, also known as “perc,” is a VOC used by U.S. dry cleaners to remove stains from clothing.24 Perc is a solvent that is mixed with a low amount of water or other liquids in commercial dry-cleaning machines.

Naphthalene (pesticide in mothballs)

Mothballs are small balls of pesticides, usually naphthalene, that turn from solid to a toxic vapor that kills moths and their larvae. Naphthalene is a VOC that is formed as a white solid. Inhalation or contact with naphthalene is associated with anemia, liver damage and neurologic conditions, among other effects. Long-term exposure to naphthalene may cause cancer.

Long-term exposure to naphthalene (found in mothballs)may cause cancer.

Mothballs should only be used sparingly, if at all. Consider trying environmentally friendly alternatives such as cedar balls or cedar chests to kill or repel moths, or other natural moth repellents such as dried lavender.

How to stop dangerous indoor air pollutants

Filtration technology for particles is not the same as the technology that is used to filter gases and chemicals.

Particles have a solid or liquid physical state. The smallest particle is approximately 0.003 microns in diameter, and gases can be substantially smaller than that. Some pollutants – such as tobacco smoke – are made up of both particles and gases.

The technology for removing particles and gases are different.Even if the sole pollutant is cigarette smoke, there need to be two technologies to remove cigarette smoke from the air.

Removing particles from indoor air

A HyperHEPA filtration system will remove nearly all of the liquid and solid particles from an indoor environment. HyperHEPA filtration technology filters the highly dangerous and extremely abundant ultrafine particles all the way down to 0.003 microns, or ten times smaller than a virus and 100 times smaller than a HEPA filter in the best scenario. HyperHEPA effectively filters the smallest particles that exist.

HyperHEPA effectively filters the smallest particles that exist.

IQAir’s HyperHEPA filtration is tested and certified by an independent, third-party laboratory to ensure it is effectively filtering ultrafine particles down to 0.003 microns.

Removing gases, odors, and chemicals from indoor air

What’s needed for efficient gas, odor and chemical removal is a combination of:

  • correct media for a particular pollutant
  • adequate contact time with the media
  • sufficient particle pre-filtration

The GC MultiGas combines a HyperHEPA pre-filter with 12 pounds of gas-phase media, capturing airborne particles (including ultrafine) and high-performance gas, odor, chemicals, and tobacco smoke filtration.

Which is the best air purifier for me?

Use our Help Me Choosetool to quickly find the best solution for you.

You’ll check off your concerns such as:

  • airborne allergens (pets, dust, dust mites, mold spores, pollen)
  • asthma
  • tobacco smoke

Step 2 asks the space you need your air cleaned. All you have to do in Step 3 is view your personalized recommendations. It’s that easy!

Finding the best solution for your indoor air quality issues can seem daunting. However,with a little knowledge and a helpful tool like the IQAir Consumer Buyers’ Guide, you’re on your way to cleaner air.

The number one air cleaning solution for your home.

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