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What is PM2.5? The Key to Healthy Indoor Air

When it comes to air quality, there are a lot of niche terms, which are sometimes confusing. One of these popular terms is “PM2.5,” in your readings, you may wonder: “What is PM2.5?” In the quest for cleaner indoor and outdoor air, understanding what PM2.5 is is crucial. PM2.5 refers to particulate matter 2.5 μm (micrometers) in diameter or smaller. These tiny particles, much smaller than the width of a human hair, can penetrate deep into our lungs and even enter our bloodstream, posing significant health risks. This article delves into the types of pollutants encompassed by PM2.5, the recommended safe levels for indoor and outdoor environments, the adverse health effects associated with breathing in these particles, and steps to mitigate PM2.5 pollution.

Photo of skyline showing clouds and electric towers during golden hour

What types of pollutants make up PM2.5?

When one first learns about particulate matter, one may wonder what PM2.5 is. PM2.5 is a complex mixture of pollutants that includes but is not limited to:

  • Combustion Particles: Emitted from vehicles, power plants, and residential burning.
  • Organic Compounds: Created by industrial processes, vehicle emissions, and natural sources.
  • Metals: Includes lead, nickel, and cadmium, often originating from industrial emissions.
  • Biological Components: Such as pollen, mold spores, bacteria, and viruses.

These pollutants originate from various sources, including industrial emissions, vehicle exhaust, wildfires, agricultural burning, and even household activities such as cooking and smoking. You may inhale PM2.5 particles without knowing it, so awareness of PM2.5 is essential.

Are there safe levels of PM2.5?

The World Health Organization (WHO) has set guidelines for PM2.5 levels to minimize health risks:

  • Outdoor Air: The WHO guideline for annual average PM2.5 levels is five µg/m3. For 24-hour exposure, the recommended limit is 15 µg/m3.
  • Indoor Air: There are no universally accepted standards for indoor PM2.5 levels. However, it’s advised to keep indoor levels as low as possible, ideally not exceeding the outdoor air quality guidelines set by the WHO.

A 2022 study measured indoor air in Southeastern homes during Thanksgiving. As occupancy increased, so did PM2.5 – from 3.0 to 5.3 µg m–3. When cooking started, PM2.5 levels increased upwards of 20 µg m–3. The study concluded that higher occupancy levels can increase particulate, and cooking and cleaning are among the leading causes of indoor air quality concerns. 

It is important to note that different areas of the world and seasons will have various levels of risk and exposure to PM2.5 particles. It is essential to look at air quality before arriving on a trip, especially if you are sensitive to PM2.5 particles. Keeping an eye on the news so you are aware of any fires, mold outbreaks, or any other adverse events can allow you to mitigate risk of inhaling these particles.

Where is the cleanest air?

The national average PM2.5 concentrations have decreased by 33% over the last 22 years. As of 2022, the Northern Rockies, Southwest, and Northeast had the lowest levels of PM2.5.

How can I reduce PM2.5 exposure?

Reducing exposure to PM2.5 requires a multifaceted approach, both at the individual and community levels:

  1. Improve Ventilation: Ensure adequate ventilation in indoor spaces to dilute pollutants. Use air purifiers with HEPA filters to capture PM2.5 particles.
  2. Reduce Indoor Sources: Minimize activities that generate PM2.5, such as smoking indoors, burning candles, and cooking without proper ventilation.
  3. Monitor Air Quality: Stay informed about the outdoor air quality in your area and minimize outdoor activities when PM2.5 levels are high. is a great EPA-operated air quality surveillance tool!
  4. Support Clean Energy: Advocate for and support policies and technologies that reduce emissions from vehicles and industrial sources.
  5. Plant Trees: Vegetation can help filter PM2.5 from the air, so supporting and participating in tree-planting efforts can improve air quality.
  6. Use Masks: In areas with high levels of PM2.5, wearing masks designed to filter out fine particles can provide personal protection.

Understanding and mitigating PM2.5 pollution is essential for protecting public health. Individuals and communities can contribute to a cleaner, healthier environment for all by reducing exposure to these harmful particles.

Lead Editor (IAQ), Clinical BacteriologistJessica Gunoskey
Jessie is the lead editor for Air Koality, overseeing all IAQ guides to ensure accuracy and quality. She holds a degree in Molecular & Infectious Disease Biology from Washington College in addition to working for multiple top-rated universities, such as UConn and UPenn. Not only does she write and edit, but she also is a STEM tutor and microbiologist!

Expertises: microbiology, infectious disease, biology, air quality

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