The Indiana Department of Environmental Management declared two Air Quality Action Days for Northwest Indiana this week.
On Monday, IDEM announced that Monday and Tuesday are Air Quality Action Days for the region, according to the news release. North Central Indiana — which includes Elkhart, South Bend and Warsaw — was included in Tuesday’s alert.
The agency cited high ozone levels as the reason for the alert, saying they’re unhealthy for sensitive groups. The U.S. Environmental Protection Agency defines sensitive groups as people with heart or lung diseases, those with diabetes, older adults and children.
Hot temperatures, sunny skies and light winds are expected throughout the region, according to the announcement, which builds high surface pressure. Buildup of pollutants over Lake Michigan is also a contributing factor, according to the announcement.
Although the heat index is high, IDEM officials said in an email that “doesn’t directly affect air quality.” According to the National Weather Service, as of about 3 p.m. Monday, Lake County’s heat index was about 90 degrees and Porter County’s was about 88 degrees.
“The heat index is the ‘feels like temperature’ factored by accounting for air temperature and humidity,” an IDEM spokesperson’s email said. “Air temperatures and dewpoints are considered individually when making an air quality forecast.”
High dewpoints can limit chemical reactions that produce ozone, according to IDEM.
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“While hot weather is often associated with higher ozone levels, very high humidity can suppress ozone to some extent,” their statement said.
According to previous IDEM announcements, the department last issued an Air Quality Action Day for July 8 in Northwest Indiana.
According to Post-Tribune archives, IDEM issues Air Quality Action Days when fine particulate matter or ozone levels will be high throughout the day. The department announced at the beginning of May that it will issue local Air Quality Advisories when short-term fine particulate matter levels increase overnight or in early morning.
In 2025, IDEM declared Air Quality Action Days for ozone levels in Northwest Indiana, according to Post-Tribune archives, and eight were called for high fine particulate matter levels.