The indoor air quality index (IAQI) is a numerical scale measuring pollutant concentrations inside buildings, ranging from 0 (clean) to 500 (dangerous). The U.S. Environmental Protection Agency (EPA) uses this system to evaluate health risks from common indoor contaminants.
IAQI scales differ by pollutant type. For particulate matter (PM2.5), the scale ranges, while for gases like carbon monoxide, it goes. Each pollutant has its own index, which combines to create an IAQI score.
Monitoring devices measure pollutant levels in micrograms per cubic meter (µg/m³) or parts per million (ppm). These measurements convert to an index value using EPA-standardized charts. For example, a PM2.5 reading of 35.5 µg/m³ converts to an IAQI of 51, falling in the "moderate" category.
Common indoor pollutants include:
Schools, offices, and homes use IAQI to assess ventilation needs and health risks. The EPA recommends maintaining IAQI below 50 for good air quality. Levels above 100 may require immediate action, such as improving ventilation or using air purifiers.
For example, a classroom with an IAQI of 60 from recent painting likely needs temporary ventilation adjustments until VOC levels drop. Similarly, homes near wildfires may see PM2.5 levels spike, requiring air filtration.
Many assume outdoor air quality directly translates to indoor levels. However, indoor air can be 2-5 times more polluted than outdoor air due to activities like cooking, cleaning, or off-gassing from furniture. The EPA notes that people spend 90% of their time indoors, making IAQI important for long-term health.
Another misconception is that air quality monitors measure all pollutants equally. In reality, most consumer devices focus on PM2.5 and CO₂, while professional monitors assess a broader range, including VOCs and radon. For accurate IAQI readings, specialized equipment is often necessary.
When I installed an air quality monitor in my home office, I noticed spikes in VOCs after using certain cleaning products. Adjusting to low-VOC alternatives dropped the IAQI, demonstrating how small changes impact air quality.
The indoor air quality index differs from the outdoor Air Quality Index (AQI) in scale and sources. Outdoor AQI measures pollutants like ozone and nitrogen dioxide, while IAQI focuses on particles and gases from indoor activities.
To lower IAQI, the EPA recommends: