Outdoor air pollution usually makes all the major air quality headlines.
A flight is canceled to Delhi because smog is too dense.1 A red alert for outdoor air pollution is declared due to record levels of dangerous outdoor pollutants.2 And nearly 7 million people die prematurely each year from causes linked to air pollution, including heart disease and respiratory conditions.3
In comparison, air pollution in your home or office doesn’t seem like breaking news.
Understanding the relationship between outdoor and Indoor Air Quality (IAQ) is your strongest weapon against its effects on your health. Your behavior and environment both influence the interaction between indoor and outdoor pollutants, so changing both your habits and your home is crucial to minimizing outdoor air pollution’s effect on indoor air.
How do outdoor air pollutants get indoors?
Indoor pollution can be even more deadly because it affects you in places where you spend 80% or more of your time each day.4
In fact, at home, at work, and at school, indoor air pollution levels are typically 2-5 times higher than outdoor pollution levels and can quickly become 100 times worse than outdoor air pollution.5,6
But what makes it so much deadlier than outdoor air pollution?
First, know that outdoor air pollution is often measured in three ways:
- PM10: Particulate matter that’s smaller than 10 microns, such as dust, pollen, and mold (for reference, a human hair is 50-70 microns in size). Many outdoor PM10 particles have natural sources.
- PM2.5: Particulate matter that’s smaller than 2.5 microns. Most PM2.5 in outdoor air is produced by human activity, such as vehicle exhaust, factory emissions, and smoke from burning wood or other biomass fuels. PM2.5 also encompasses ultrafine particles (UFPs), which are smaller than 0.1 microns. UFPs are small enough to penetrate through your lung tissue into your bloodstream.
- Tropospheric (ground-level) ozone: Often just called smog, ground-level ozone (O3) results from heat reacting with pollutants low in the atmosphere. Gases from vehicles and industrial processes, such as nitrogen oxide (NOx) and volatile organic compounds (VOCs) are the most common sources of ozone.
Concentrations of these outdoor pollutants rise and fall constantly because of changes in the weather, climate, and human activity.
For example, outdoor pollutants can build up in the lower atmosphere due to temperature inversions, which happen during periods of cold weather when warm air rises into the upper atmosphere and traps cold air beneath it, causing pollutants to build up at low altitudes.7 Concentrations may also rise quickly in the mornings during rush hour traffic, but subside once traffic diminishes and wind and heat clear the air of excess pollutants.8 In a sense, the earth has its own natural air-purifying technology that disperses outdoor pollutants far and wide, keeping most of the planet’s air safe to breathe.
But indoor pollutants aren’t always exposed to any similar processes to minimize their concentrations. Ventilation often brings in fresh outdoor air to dilute indoor pollutants, but can also introduce even more pollutants into your indoor air from the polluted outdoor air.
And outdoor air pollutants infiltrate your indoor air in ways that may not be immediately obvious. The most common ways outdoor air pollution affects IAQ are through open windows and doors as well as cracks in walls, doors and window sealants.
Open windows and doors
When your home or building feels stuffy, your first instinct may be to open windows and doors to let in “fresh air.” Bringing in oxygenated outside air can be a good idea, but outdoor air can be polluted. When outdoor pollutant levels are high, ventilating the indoors with outdoor air can make your pollution worse.
It’s typically a good idea to regularly let in lots of outdoor air to decrease build-ups of indoor pollutants and toxic gases, such as ultrafine particles and carbon dioxide (CO2). But your exposure to outdoor PM10 and PM2.5 increases significantly when polluted outdoor air infiltrates your home or office in such large amounts.9
Outdoor ground-level ozone and other outdoor gases can also enter a home or building through ventilation processes and even react with chemicals in your building materials to create harmful chemical byproducts.10 Research shows that indoor ozone from outdoor sources, even at low levels, can trigger asthma symptoms and lead to respiratory problems.11,12
Cracks in walls and windows
The most sinister points of entry for outdoor air pollutants are the tiny, often undetectable cracks, openings, and gaps in your walls and windows.
Older, less energy-efficient homes are especially susceptible to leaks of outdoor pollutants indoors because they’re less airtight than newer, energy-efficient homes specifically designed to limit the rate of exchange between indoor and outdoor air.13
Older homes also tend to be more damaged by age and weather, breaking down seals and weather-stripping around doors, windows, and other openings that can do little to keep polluted outdoor air from seeping in.14
On the other hand, newer, airtight homes have their downsides. Because the exchange rate between indoor and outdoor air is low, pollutants that do get inside build up more quickly because they have nowhere to escape
Some of these pollutants, such as ozone and nitrogen dioxide found in vehicle exhaust, react with off-gassing building materials and furniture as well as with cleaning chemicals, creating new compounds like formaldehyde that make indoor air even more toxic.15
How do I minimize my exposure to pollution?
No matter where you are, you’re always at risk for exposure to airborne pollutants from both indoor and outdoor sources. Try some of the following tips to help keep your indoor air clean:
- Monitor your Indoor Air Quality (IAQ). Live air quality data lets you know immediately when your air is becoming too polluted and arms you with the knowledge you need to mitigate its sources and effects. AirVisual Pro by IQAir is a portable air quality monitor that uses cutting-edge laser technology to measure real-time air pollution levels so that you always know what’s in your air.
- Control indoor pollution sources. Mold, dust mites, gases from cooking and heating, and tobacco smoke are the most significant sources of indoor air pollution. To limit these sources:
- Ventilate your home—wisely. Open windows and use fans regularly to disperse indoor pollutants. But if outdoor pollution rises to unhealthy levels, consider keeping your doors and windows closed until air quality improves. In the meantime, use a high-performance air purifier with a gas and odor filter to filter both particles and gases from your indoor air.
- Use a high-performance air purifier. Indoor air inevitably becomes polluted from outdoor pollution. When full source control is difficult or impossible, use the IQAir HealthPro® Plus, a high-performance air purifier with HyperHEPA® filtration technology, to remove 99.5% of pollutant particles down to 0.003 microns from your indoor air.
- Use a whole-house or commercial air purification solution. The Perfect 16®whole-house air purifier by IQAir filters both outdoor and recirculated indoor air with advanced HyperHEPA filtration. Nanomax™ high-efficiency panel filters are a high-performance, cost-effective choice designed for commercial HVAC systems.
- Take clean air with you wherever you go. Clean air isn’t always guaranteed, especially at work or while traveling. Breathe pure air anytime, anywhere with the Atem® by IQAir, a personal air purifier that instantly creates a clean air bubble free of 99% of pollutant particles down to 0.003 microns in your personal breathing zone.
You spend 80% or more of your time indoors during an average day. Make a few small changes to your habits and your indoor environment so that you can breathe the purest possible indoor air, keeping your head clear and your lungs clean.
 Meza S. (2017). New Delhi air pollution causes United Airlines flight cancellations.
 China’s capital issues first major smog alert of winter. (2018).
 The Lancet Commission on pollution and health. (2017).
 Leung DYC. (2015). Outdoor-indoor air pollution in urban environment: Challenges and opportunity.
 Indoor air quality. (n.d.)
 The inside story: A guide to indoor air quality. (n.d.).
 Kaltenegger L. (2011). Atmosphere, temperature inversion.
 Zhang K, et al. (2013). Air pollution and health risks due to vehicle traffic.
 Improving ventilation and indoor air quality during wildfire smoke events. (2015).
 Zhao H, et al. (2015). A method to measure the ozone penetration factor in residences under infiltration conditions: application in a multifamily apartment unit.
 Ozone and your health. (2014).
 Ozone and indoor chemistry. (2011).
 Stephens B. (2015). Infiltration of outdoor pollutants: How building airtightness and pollutant characteristics affect the transport of outdoor air pollution into the indoor environment.
 Azimi P, et al. (2016). Modeling the impact of residential HVAC filtration on indoor particles of outdoor origin.
 Steinemann A, et al. (2017). Ten questions concerning green buildings and indoor air quality.
Air Quality Life is brought to you by The IQAir Group, the world’s leading innovator of Indoor Air Quality solutions since 1963. This online publication is designed to educate and inform the public about the latest research and news affecting indoor and outdoor air quality.