The Post uses data from World Air Quality Index and updates the page every 15 minutes. Data for some cities may not update regularly.

AQIAir Pollution LevelHealth Implications
0-50GoodAir quality is considered satisfactory, and air pollution poses little or no risk.
51-100ModerateAir quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution.
101-150Unhealthy for Sensitive GroupsMembers of sensitive groups may experience health effects. The general public is not likely to be affected.
151-200UnhealthyEveryone may begin to experience health effects; members of sensitive groups may experience more serious health effects.
201-300Very UnhealthyHealth warnings of emergency conditions. The entire population is more likely to be affected.
301+HazardousHealth alert: everyone may experience more serious health effects.

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