Southern Fairfield County has an Air Quality Alert on Tuesday with high levels of ozone.

The alert is in effect from 11 a.m. to 11 p.m.

Temperatures will be about 10 degrees warmer than Monday with temperatures rising into the mid-80s

It will also be more humid and more muggy this evening.

Connecticut’s worst air pollution ranking comes from ozone. The state is ranked 12th as the worst polluted with ozone. The ranking includes New York-Newark, N.J. and Pennsylvania.

Often called smog, ozone pollution is harmful to breathe. Ozone aggressively attacks lung tissue by reacting chemically with it. When ozone is present, other harmful pollutants can be created.

Ozone develops in the atmosphere from gases that come out of tailpipes, smokestacks and many other sources. When these gases come in contact with sunlight, they react and form ozone smog.

The American Lung Association “State of the Air Report” gives all of Connecticut an F for high levels of ozone pollution. The annual air quality report card tracks Americans’ exposure to unhealthful levels of ozone and particle pollution, both of which can be deadly.

The methodology of the report determined a “weighted average” of ozone pollution based on the number of “orange” and “red” days.

Orange days are when the air quality index is between 101 and 150, on days when temperatures are in the 80s and 90s and winds are light. Red days are when air quality index is between 151 and 200, on days that are hot, hazy and humid, the air is stagnant and skies are sunny with little chance of precipitation.

Fairfield County has the highest number of high ozone days in Connecticut with an average of 25.8 days. Last year.It had 42 orange days and 18 red days.

High ozone levels are expected most of the week with temperatures in the 80s.

The forecast

Today: Mostly sunny, with a high near 84. Light and variable wind becoming south 5 to 9 mph in the afternoon.

Tonight: Mostly clear, with a low around 63. South wind around 5 mph becoming calm in the evening.

Wednesday: Mostly sunny, with a high near 80. Light and variable wind becoming south 5 to 10 mph in the morning.

Thursday: A chance of showers and thunderstorms, then showers likely and possibly a thunderstorm after 2 p.m. Cloudy, with a high near 75. South wind around 10 mph. Chance of precipitation is 60 percent New rainfall amounts between a quarter and half of an inch possible.

Thursday Night: A 50 percent chance of showers and thunderstorms before 2 a.m. Mostly cloudy, with a low around 62.

Friday: Mostly sunny, with a high near 82.

Wednesday Night: A 50 percent chance of showers and thunderstorms. Mostly cloudy, with a low around 66. South wind around 9 mph.