Air Quality and Your Health: Understanding the EPA’s Air Quality Index

What is the Air Quality Index (AQI)?

The Air Quality Index (AQI) is a standardized system developed by the U.S. Environmental Protection Agency (EPA) to communicate how clean or polluted the air is and what associated health effects might be a concern. The AQI runs from 0 to 500 — the higher the value, the greater the level of air pollution and the greater the health concern.

The Six AQI Categories

| AQI Value | Category | Color | Health Implications |
|———–|———-|——-|———————|
| 0-50 | Good | Green | Air quality is satisfactory |
| 51-100 | Moderate | Yellow | Acceptable for most; unusually sensitive people may experience symptoms |
| 101-150 | Unhealthy for Sensitive Groups | Orange | Sensitive groups may experience health effects |
| 151-200 | Unhealthy | Red | Everyone may begin to experience health effects |
| 201-300 | Very Unhealthy | Purple | Health alert: everyone may experience serious effects |
| 301-500 | Hazardous | Maroon | Health emergency; everyone is affected |

What Pollutants Does the AQI Measure?

The EPA calculates the AQI based on five major air pollutants:

  • Ground-level ozone (O₃): Forms when sunlight reacts with pollutants from vehicles and industry; worsens asthma and respiratory conditions
  • Particle pollution (PM2.5 and PM10): Tiny particles from fires, dust, and combustion; penetrate deep into lungs
  • Carbon monoxide (CO): Colorless, odorless gas from incomplete combustion
  • Sulfur dioxide (SO₂): Primarily from power plants burning fossil fuels
  • Nitrogen dioxide (NO₂): From vehicle emissions and power plants

    • Who is Most at Risk?

    Sensitive groups include:

    • Children (lungs still developing)
    • Elderly individuals
    • People with asthma, COPD, or other lung diseases
    • People with heart disease
    • Pregnant women
    • Outdoor workers

      • Protecting Yourself on High-AQI Days

      When AQI is in the Orange Range (101-150)

    • Sensitive groups should reduce prolonged outdoor exertion
    • Keep windows closed if outdoor air quality is worse than indoor
    • Avoid exercising near high-traffic roads

      • When AQI is Red or Above (151+)

    • Everyone should reduce outdoor activity
    • Use HEPA air purifiers indoors
    • Wear a properly fitted N95 mask outdoors if activity is necessary
    • Keep pets indoors
    • Avoid burning candles, fireplaces, or incense

      • During Wildfire Smoke Events

    • Stay indoors with windows and doors closed
    • Run your HVAC system on recirculate mode
    • Use air purifiers with HEPA filters
    • Follow evacuation orders if issued
    • Sign up for local emergency alerts

      • How to Check Your Local AQI

    • AirNow: airnow.gov (EPA’s official real-time AQI tool)
    • Purple Air: Community air sensor network with hyperlocal data
    • Weather apps: Most include AQI data
    • EPA’s My Environment: myenvironment.epa.gov

      • Long-Term Solutions

      What You Can Do

    • Drive less; use public transit, bike, or walk
    • Avoid idling your vehicle
    • Use electric lawn equipment instead of gas-powered
    • Refuel your car in the evening (reduces smog formation)
    • Use energy-efficient appliances
    • Support clean energy policies

      • What EPA and States Are Doing

    • Tightening vehicle emissions standards
    • Reducing industrial pollution through permitting requirements
    • Expanding electric vehicle infrastructure
    • Updating the National Ambient Air Quality Standards (NAAQS)

      • Resources

    • AirNow: airnow.gov
    • EPA Air Quality: epa.gov/air-quality
    • CDC Air Quality: cdc.gov/air
    • Asthma and Allergy Foundation: aafa.org
    • Sign up for AQI alerts: enviroflash.info