What Happens When the Air Quality Index Surpasses 500?
New York Citys smoke-clogged air reached 407 on the Environmental Protection Agencys 500-point Air Quality Index at one point this week, signifying that pollution levels were hazardous and at historically dangerous levels.
But its not the worst air quality that the United States has seen. There have been about 40 times over the past decade when the index has risen above 500, into what the E.P.A. calls Beyond the A.Q.I. Most of those instances have occurred in Western states, including California, Oregon and Washington, the E.P.A. said in an email, as wildfires spread a blanket of smoke over parts of the region.
The E.P.A. in 1999 released the current version of the six-tier index as a way to communicate to the public the density of five pollutants. A rating anywhere between 301 and 500 is considered hazardous, and air quality at that level will trigger health warnings. At that level and beyond, everyone should stay indoors and reduce activity levels. Use the same information that is for the hazardous category, the E.P.A. advises.