The Air Quality Advisory issued by the Department of Environmental Protection is not the result of wildfire smoke, as it was last week, but instead ozone. Ground-level ozone is the main ingredient in smog, and is most likely to hit unhealthy levels on hot days in urban areas, according to the Environmental Protection Agency.

Temperatures across Massachusetts are expected to clear 90 degrees on Tuesday, the second straight day of sweltering conditions amid a heat wave blanketing the state. It could get as hot as 95 in parts of the Bay State,