Understanding Air Quality Alerts and Index Codes in the US and Canada.
Originally Published 2 years ago — by The Washington Post
The U.S. Air Quality Index measures five major pollutants and ranges from 0 to 500, with higher values indicating worse air quality. Code Green represents good air quality, while Code Purple means the air is hazardous and serves as a "health warning of emergency conditions." The Environmental Protection Agency recommends reducing exposure to pollution, especially for those at increased health risk, such as people with asthma.