Unhealthy air quality is being predicted for “sensitive groups” for much of Connecticut on Monday, Aug. 17, where temperatures are expected to reach in the mid 90s.

The second heat wave of the summer is predicted to start today.

A forecast of “Unhealthy for Sensitive Groups” indicates increased likelihood of respiratory symptoms and breathing discomfort in active children and adults with respiratory disease, such as asthma, as well as the elderly.

Ground level or “bad” ozone primarily occurs during very warm summer days. Strong sunshine causes chemical reactions of air pollutants emitted from motor vehicles, power plants and industry and household activities, forming ozone.

Warmer weather can bring high levels of ground level ozone (O3) and fine particulate matter (PM2.5). These two air pollutants pose serious health risks to “sensitive groups.”

The Department of Environmental Protection (DEEP) monitors, tracks and forecasts daily air quality levels across Connecticut for ozone from May 1 through Sept. 30, and for fine particulate matter each day of the year.

Fairfield County most polluted

Earlier this year, Fairfield County was named the most polluted county for ozone in all of Connecticut, New York, New Jersey and Pennsylvania, according to the American Lung Association’s (ALA) State of the Air 2015 report.

“The State of the Air report results should be of concern for all Connecticut residents,” said Dr. David Hill, a pulmonologist with Waterbury Pulmonary Associates and a member of the Connecticut ALA Leadership Board.

“Ozone pollution levels are not improving and particle pollution shows minimal improvement,” Hill said. “This is not the progress we need to protect and improve the health of Connecticut’s residents.”

Hill said poor air quality causes lung disease, worsens lung disease in those who already suffer from asthma and COPD, and increases the risk for heart attack and stroke.

The State of the Air report uses official monitors for the two most widespread types of pollution, ozone and particle pollution.

Ozone (smog) is the most widespread air pollutant, created by the reaction of sunlight on emissions from vehicles and other sources. When ozone is inhaled, it irritates the lungs, almost like a bad sunburn, according to the ALA.

It can cause immediate health problems that continue days later. Ozone can lead to wheezing, coughing, asthma attacks and premature death.

Particle pollution (soot) is a deadly cocktail of ash, soot, diesel exhaust, chemicals, metals and aerosols that can spike dangerously for hours to weeks on end, according to the ALA.

The body’s natural defenses, coughing and sneezing, fail to keep these microscopic particles from burrowing deep within the lungs, triggering serious problems such as asthma and heart attacks, strokes, lung cancer and even early death.

Exposure to particle pollution has been compared to rubbing sandpaper on the lungs, the ALA said.

Fairfield County improved a letter grade for short-term particle pollution in the State of the Air 2015 report. This is in keeping with a trend seen across the nation of lower particle pollution levels.

Nationwide, more than four in 10 Americans — or about 138 million people — live in counties where ozone or particle pollution levels make the air unhealthy to breathe, according to the ALA.

The 16th annual national report card looked at air pollution data collected from 2011 to 2013.