One year after the last publication, DEQ revised its Modeling Guidelines again in June 2017. Many of the revisions involve simple updates to referenced materials such as EPA websites. The more substantive changes were largely due to EPA's revised (January 2017) Guideline on Air Quality Models (40 CFR 51 Appendix W), which changed the preferred status of the CALPUFF model; adjusted the way NO2 is modeled; and addressed precursor pollutants, particularly for PM2.5 and ozone modeling.
Additional changes to DEQ's Guidelines include added or modified language regarding screening modeling/techniques; characterization of certain source types (e.g., capped/horizontal stacks, area sources such as open pits and line sources, open doors, and flares); meteorological data requirements, including a section on the use of Mesoscale Model Interface Program (MMIF) data; GEP stack height; and urban-area stacks. Lastly, a new section on H2S modeling was added while the state-required SO2 modeling section was removed.