Understand what AQI values mean for your health and outdoor activities
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The Air Quality Index (AQI) is a standardized indicator developed by environmental agencies to communicate how polluted the air currently is or how polluted it is forecast to become. The AQI translates complex air quality data into a simple numerical scale from 0 to 500, with higher values indicating greater levels of air pollution and increased health concerns.
AQI considers five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (PM2.5 and PM10), carbon monoxide, sulfur dioxide, and nitrogen dioxide. The AQI value is determined by the pollutant with the highest concentration at a given time.
Good (0-50): Air quality is satisfactory, and air pollution poses little or no risk. Ideal conditions for all outdoor activities.
Moderate (51-100): Air quality is acceptable. However, there may be a risk for some people who are unusually sensitive to air pollution, particularly those with respiratory conditions.
Unhealthy for Sensitive Groups (101-150): Members of sensitive groups may experience health effects. The general public is less likely to be affected. Sensitive groups include children, older adults, people with lung diseases like asthma, and people with heart disease.
Unhealthy (151-200): Some members of the general public may experience health effects; members of sensitive groups may experience more serious health effects. Everyone should consider reducing prolonged outdoor exertion.
Very Unhealthy (201-300): Health alert: The risk of health effects is increased for everyone. Everyone should avoid prolonged outdoor exertion; sensitive groups should avoid all outdoor activity.
Hazardous (301-500): Health warning of emergency conditions. The entire population is more likely to be affected by serious health effects. Everyone should avoid all outdoor physical activity.
This tool provides general guidance based on EPA AQI standards. Individual responses to air quality vary based on personal health conditions, age, fitness level, and duration of exposure. AQI values represent average conditions over several hours and may not capture short-term spikes in pollution.
Always consult with healthcare providers about personal air quality sensitivities, especially if you have respiratory or cardiovascular conditions. Local conditions may vary within a region, so check the most localized AQI reading available for your specific area.
You can find current AQI readings on AirNow.gov, local weather apps, environmental agency websites, and many weather forecasts. Most smartphone weather apps now include AQI data. Some states and cities also have their own air quality monitoring websites.
No. Different countries use different AQI scales. This tool uses the United States EPA AQI scale (0-500). Other countries like China, India, and the European Union use different scales and calculation methods. Always confirm which AQI standard is being used in your location.
AQI increases due to higher concentrations of air pollutants. Common causes include vehicle emissions, industrial activity, wildfires, dust storms, temperature inversions that trap pollutants, and weather conditions that prevent pollutant dispersion. Seasonal factors like summer heat (which increases ozone) and winter wood burning also affect AQI.
Yes, most people can exercise outdoors when AQI is moderate (51-100). However, if you're unusually sensitive to air pollution or have respiratory conditions, consider monitoring your symptoms and reducing intensity if you experience discomfort. Sensitive individuals should pay more attention at the higher end of the moderate range (90-100).
When AQI reaches unhealthy levels (151+), everyone should limit prolonged outdoor exertion. Move activities indoors, close windows, use air purifiers if available, and avoid areas with heavy traffic. Sensitive groups should avoid outdoor activities entirely. If you must go outside, consider wearing an N95 mask for particle pollution.
Yes, outdoor AQI affects indoor air quality, especially if windows are open or the building isn't well-sealed. During poor air quality days, keep windows closed, use HEPA air purifiers, run air conditioning with recirculation mode, and avoid activities that worsen indoor air like cooking without ventilation or burning candles.
PM2.5 refers specifically to fine particulate matter (particles 2.5 micrometers or smaller). AQI is a broader index that considers PM2.5 along with other pollutants like ozone, PM10, carbon monoxide, sulfur dioxide, and nitrogen dioxide. The overall AQI is determined by whichever pollutant has the highest concentration.
AQI can change throughout the day as weather conditions shift, traffic patterns change, and pollutant levels fluctuate. Many monitoring sites update AQI hourly. It's wise to check AQI in the morning before planning outdoor activities and again before extended outdoor time, especially during wildfire season or high pollution periods.