ESSI

Understanding the U.S. Air Quality Index

Tips on understanding the U.S. AQI

TIP

  • Good AQI does not mean zero risk of health effects will absolutely occur.
  • The AQI should not be used for low-cost sensor readings indoors or readings less than 1 hour.
  • The AQI of multiple pollutants should not be added together.
  • There are many reasons why an air quality index reported by the host country government differs from the U.S. AQI.

WHY

  • The AQI is based on scientific evidence, which has not identified a level of air pollution that has zero risk of health effects, The science describes how risk differs between higher and lower air pollution levels in a group of people and does not predict how any individual will be affected.
  • The U.S. AQI is based on the science for outdoor air pollution and longer periods of time.
  • The science is not clear whether the health risks are larger when multiple pollutants are high at the same time.
  • Different formulas or pollutants may be used to calculate the index. Also, pollutant levels can vary across locations in a city.