ENV-13-11 Challenges for Modeling Compliance with Short-term SO2, NO2 and PM2.5 Ambient Standards

Description:

U.S. EPA’s revisions to National Ambient Air Quality Standards (NAAQS) for PM2.5, SO2 and NO2 and new implementation procedures provide significant challenges regarding the application of dispersion models to assess compliance. Given that these new NAAQS are very stringent, the customary degree of overestimation that is intentionally designed into the present Modeling Guideline (40 CFR Part 51, Appendix W1) methods need to be reassessed. EPA released draft implementation policy documents to address compliance assessments for PM2.5 and SO2 earlier in 2013. This paper provides preliminary review and initial experience with these new procedures, and features the following topics: • PM2.5 modeling of secondary particulate matter formation. • Hybrid modeling and monitoring approaches for compliance with the 1-hour SO2 NAAQS. • Assessment of refined approaches to simulate the NO to NO2 conversion rate for NO2 compliance modeling. • Refined modeling approaches recently submitted to EPA by EPRI. • Experiences with a newly released version of AERMOD (Version 12345) that is intended to address noted deficiencies for modeling low wind speeds.