The U.S. Environmental Protection Agency defended its decision Monday for last week's decision to name Lake and Porter counties as areas not in attainment of federal ozone standards.
Eight counties and parts of three counties in the tri-state Chicago metropolitan area did not meet the 2008 National Ambient Air Quality Standards for ozone.
Officials in Indiana criticized the findings in a statement Friday and said ozone monitor data from the last few years show Lake and Porter counties are in compliance.
A statement from EPA issued Monday said Lake County in Illinois was found to be violating the eight-hour ozone standard, but Lake and Porter counties in Indiana were found to be contributing to the violations. The designation is the first part of implementing ozone standards that were revised in 2008.
Ground-level ozone, a smog component, can cause human health problems and damage to forests and agricultural crops.
EPA expects areas designated as marginal nonattainment – such as Lake and Porter counties – should meet the standards in three years.
"History shows that cleaner air, better health and economic growth go hand-in-hand," said EPA spokeswoman Phillippa Cannon via email Monday.
The EPA said the designation is the result of studying air quality monitoring data, recommendations submitted by states and tribes, and other technical information including emissions, commuting patterns, population growth, weather patterns and topography.
With Lake and Porter counties being in nonattainment, both will continue to be recipients of federal money from the Congestion Mitigation and Air Quality Program. The program funds projects that improve air quality and reduce congestion. Both counties had been maintenance areas after gaining compliance with old ozone standard in 2010 before it was revised.