The temperature on any given summer day may be in the 80s or 90s. So why does it feel so much hotter and oppressive at times? That's the heat index doing its thing. Here's how it works: What is the ...

Smoke from wildfires in Canada has drifted into the U.S., prompting air quality alerts for Americans as it continues to spread. But when officials and forecasters classify a city's air as "unhealthy" ...

The color-coded Air Quality Index categories you’ll find on the Environmental Protection Agency’s AirNow website rank air quality on a 500-point scale and are meant to give the public an easy way to ...