The Indiana Department of Environmental Management is warning of more high ozone levels Thursday that could cause health problems for children, the elderly and those with respiratory difficulties.
IDEM issued an Air Quality Action Day for ozone in Lake, Porter, LaPorte, Newton and Jasper counties.
Ozone is created on hot, still days when pollutants in gasoline, automobile emissions and other combustion engines, such as those that burn coal and other fossil fuels, are cooked by the sun.
Environmental and health agencies issue alerts when ozone levels are expected to be high and urge people to reduce vehicle trips, mow lawns early in the morning or later in the evening and reduce energy use in businesses and homes.
Thursday marks the fourth Air Quality Action Day of the week and the sixth of the year.