Indoor vs Outdoor Air Quality – What’s the Difference?

Indoor vs Outdoor Air Quality – What’s the Difference?

Since air is fluid, it can flow in and out of our homes, sometimes bringing pollutants with it. Thanks to the PurpleAir indoor and outdoor air quality monitors, you can quickly compare air quality around you to make the best decision for your home or office.

Common Outdoor Air Pollutants

There are plenty of outdoor sources impact air quality. According to the American Lung Association, the six most common factors impacting outdoor air quality are:


  • Ozone – One of the most dangerous and invisible pollutants.
  • Particulate Matter – Small solid and liquid particles in the air we breathe.
  • Nitrogen Dioxide – A harmful gas emitted when we burn fossil fuels.
  • Sulfur Dioxide – Another harmful gas emitted when we burn fossil fuels.
  • Carbon Monoxide – Another gas that forms from burning fuels.
  • Other Toxic Air Pollutants – About 200 other air pollutants can cause various diseases.

Common Indoor Air Pollutants

Indoor air pollution contains all kinds of air pollutants. The United States Environmental Protection Agency EPA says indoor pollution can include:

  • Asbestos
  • Biological Pollutants
  • Carbon Monoxide (CO)
  • Cooking stoves and ovens
  • Formaldehyde/Pressed Wood Products
  • Lead (Pb)
  • Nitrogen Dioxide (NO2)
  • Pesticides
  • Radon (Rn)
  • Indoor Particulate Matter
  • Secondhand Smoke/ Environmental Tobacco Smoke
  • Volatile Organic Compounds (VOCs)
  • Wood Smoke 

As we enter the summer months, which for many of us, is also wildfire season, here are a few ways to understand indoor and outdoor air quality.

How Does Air Pollution Move?

Opening doors and windows allows air to move freely between the indoors and outdoors. But does air still travel in and out when the doors and windows are closed?

Yes. Buildings breathe through the cracks, gaps, and mechanical equipment such as bathroom fans, fresh air intakes, and heat recovery ventilators. While this airflow volume is relatively low, it's beneficial to be aware that it can unsuspectingly bring in pollutants when the air quality is poor outside.

Air Quality Monitoring is Dynamic

As urbanization increases, the pressures on air quality from industry, environmental factors like wildfires, and everyday living also increase. In some areas, air quality changes daily because of how many cars and trucks are on the road, how many wildfires may be burning across the state, and more.

Simply knowing what is happening around us offers important ways to avoid exposure to harm.

In some homes and offices, air quality can change because of indoor pollutants that come from within the house or seep in from the outdoors. Ultimately, it helps to remember that air quality is constantly changing, and knowing what’s happening in and out of our homes and offices is crucial for monitoring this dynamic exchange between what’s indoors and outside.

Bundle Your Approach

By having an active, real-time air quality monitor inside and outside your home or office, you have immediate information you can use to reduce your exposure to harm.

If air quality is essential to you, then one of the best things you can do is have indoor and outdoor air quality sensors. Stay informed and make sure you know the air quality around you – in real-time.

Worried about air quality?

Monitor the Particulate Matter levels around the world with our free, real-time PurpleAir Map or join PurpleAir's mission to make air quality data accessible to everyone by investing in an air quality monitor for your home. 

Together, we can be informed and make changes in our daily habits and the community to improve air quality.