On May 16, 2024, the Board adopted amendments to keep Illinois’ ambient air quality standards identical in substance to the National Ambient Air Quality Standards (NAAQS). The amendments reflect two actions taken by the United States Environmental Protection Agency (USEPA) during the second half of 2023. First, USEPA updated the current ozone absorption cross-section to the recommended consensus-based cross-section value. Second, USEPA designated two new equivalent methods for monitoring ambient air quality, one for measuring concentrations of lead (pb) and the other for measuring concentrations of particulate matter (PM10). The Board’s final amendments account for these USEPA updates.
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