What are the Most Common Air Pollutants? (Indoor and Outdoors)

Did you know that air pollution is not just an outdoor problem?

It’s true.

In fact, indoor air pollution can up to 5 times worse than the outdoors, according to the U.S. Environmental Protection Agency (EPA).

So, what are the most common air pollutants that pose a hazard to your health?

And what makes air quality unhealthy outdoors and indoors?

Those are the questions we’re going to answer in this post.

If you want to know what is bad air quality and the things that contribute to it, keep reading.

After you’re done, you may want to check out a few of our posts on air purifiers. Air purifiers can help eliminate many of the airborne toxins mentioned in this post.

For the cheapest options, check out our best affordable air purifier buying guide.

For the top options, check out our top air purifier reviews which include the 10 highest rated air purifiers available.

What are the Most Common Air Pollutants?

Outdoor Air Pollutants

When you think of air pollutants, the outside environment is the first thing that comes to mind.

The EPA currently categorizes the top air pollutants for the exterior into six groups, such as:

  • Particulate matter
  • Sulfur dioxide
  • Lead
  • Ground-level ozone
  • Nitrogen dioxide
  • Carbon monoxide

Particulate matter refers to substances floating in the air, such as ash or dust.

In contrast, sulfur dioxide is the byproduct of industrial processes, including the burning of fossil fuels.

Lead enters the air through production facilities around the world, whereas ground-level ozone often evolves from vehicle exhaust entering the air space.

Both nitrogen dioxide and carbon monoxide come from vehicle exhaust, which makes any urban area prone to high pollution levels.

Currently, the California Air Resources Board lists almost 200 substances that are potential pollutants.

There are two other substances, however, that affect both the environment and the interior of your home. Asbestos and radon deserve a closer look.


Asbestos is a naturally occurring substance in the ground. Many years ago, it was experimented with as a fire-resistant material in buildings, ships, and airplanes. This substance, however, is also a hazard to people because of the fine fibers that break off from it. People breathe them in, and dangerous diseases occur many years afterward.

Air pollution from asbestos occurs both outdoors, near natural deposits, and indoors where old building materials continue to thrive. Local authorities try to control deposits that may be unearthed at times, but it’s up to homeowners to discover and remove the materials without causing them to kick up into the air.

What are the most common air pollutants? They tend to be substances that can float through the air for minutes or hours. That is how they end up being breathed in by large populations.

Radon Gas

Radon is a substance that acts a lot like asbestos except that it’s a gas instead of fine fibers. The Earth holds a lot of elements, including solids, liquids, and gases. Radon happens to be a gas that’s highly toxic to people. In fact, it’s considered as a radioactive substance.

This gas releases into the open air as it moves up through the Earth’s crust. It can spread out across a community as it impacts the air mass.

Radon can also seep into homes as it comes up from the ground. Because it’s an odorless gas, radon isn’t normally noticed unless residents test the air or notice distinct symptoms. It can be easily trapped in homes that have closed windows and doors, which makes this outdoor-indoor pollutant particularly concentrated and harmful to people.

Indoor Air Pollutants

The most common pollutants found indoors include these substances, such as:

  • Paint
  • Carpet
  • Pet dander and bugs
  • Household cleaners
  • Water damage
  • Smoke

Although your home isn’t airtight, it does hold the air mass in place. Volatile Organic Compounds (VOCs) emanating from carpets, drywall, paint and cleaning supplies will all contribute to indoor air pollution.

Pets are constantly dropping dander in the form of fur and skin cells. Cockroaches, in particular, will contribute to dander and harmful contaminant levels. These particles easily contaminate the air indoors.

Any moisture that doesn’t evaporate inside, such as from plumbing leaks or high humidity like in a basement or bathroom, can encourage mold and mildew growth.

Smoking and vaping will also impact the air mass along with any pests moving around the property.

All of these particles can become airborne, which leads to indoor air pollution.

What Makes Air Quality Unhealthy?

Human lungs have evolved to filter out a lot of contaminants, but air pollution is different.

Air quality that’s deemed as unhealthy will have a mixture of contaminants in dense concentrations.

Think of your home as a bubble.

Close all the windows and doors, and the indoor air quality depends on the particulates found in the immediate area. Dust, pet dander and material fumes can build up, which causes unhealthy air quality.

This same concept applies to outdoor air pollution. If people are constantly running their vehicles and businesses release toxic fumes into the air, the surrounding air mass will have a high concentration of particles that the lungs cannot filter out.

What is Bad Air Quality?

The government defines bad air quality by an indexing value called AQI. When particulates hit a certain threshold, cities must warn residents about bad air quality. It can range from unhealthy to very unhealthy.

When an area has poor air quality, most residents are encouraged to remain indoors with air conditioners on.

Every person has a unique immune system, which may or may not be affected by the air particulates. Anyone with a chronic condition, such as asthma, might feel more of the air’s effects than other folks.

Bad air quality often occurs with hot temperatures and lack of wind. The air seems to sit in place, which allows the sun to bake it and concentrate more pollutants in a smaller area.

The onset of cooler temperatures and even rain will help the air quality recover.

You Don’t Have to Suffer from Air Pollution

Now that you know what makes air quality unhealthy and what are the most common air pollutants, you may be wondering what can you do to protect yourself from these invisible particles.

The truth is that many of these contaminants can be removed from your indoor air by using an air purifier.

Air purifiers strip the air of harmful particles so that the air around you is clean and fresh to breathe.

If you want to see what’s available for the lowest price, take a look at our best affordable air purifier buying guide.

Or if you want to see a list of the top 10 models, visit our best home air purifier reviews page.

No matter which product you pick, an air purifier is a great device to have inside any home or office.