The IDNR is proposing to provide default background ozone concentration data to assist industry in modeling NO2 using the Ozone Limiting Method (OLM) or Plume Volume Molar Ratio Method (PVMRM). Additionally, the IDNR is revising their restricted hours of operation modeling guidance to better detail the appropriate procedure for PM2.5 modeling when PM2.5 sources are subject to annual operating hour limitations. For more information, click here.