An air quality alert was issued by the National Weather Service in Milwaukee-Sullivan at 1:52 p.m. on Wednesday, July 23.

The EPA's Air Quality Index can tell you whether breathing outside air can be harmful. Here's how to read the scale to plan ...

AirNow and PurpleAir use the Air Quality Index, or A.Q.I., a measure of air quality from 0 to 500 that is composed of six categories, from “good” to “hazardous.” ...