Implications of recent final and draft decisions to atmospheric deposition of N and S

This is a quick overview of the implications of two rules (1. recent final rule for primary PM2.5, and 2. the final PA (policy assessment) for secondary NOxSOxPM ) on total atmospheric deposition of N and S. The is given to the USFS critical loads group as part of their monthly seminar series. The recent final rule for PM2.5 (primary) lowers the standard from 12 ug/m3 to 9 ug/m3, and although it won't have any effect on total S deposition, it may contribute to small reductions in total N deposition (by 1-3 kg N ha-1 yr-1) in some areas. The recent final PA for NOxSOxPM (secondary) will not become a draft rule until later (~April 2024), but none of the options under consideration are expected to affect N or S deposition. 

Impact/Purpose

The purpose of the presentation is to summarize to the critical loads community in USFS the potential implications of two recent regulatory actions (1. Final Rule on PM2.5 (primary), 2. Final PA on NOxSOxPM (secondary)) on atmospheric deposition of N and S. This is a presentation given to the monthly USFS technical group on atmospheric deposition. We (EPA/ORD) want to make sure our partners are aware of the effects and non-effects from the recent rules on atmospheric deposition. This presentation uses all publicly available information from the Final PM2.5 Rule and from the Final PA on NOxSOxPM. 

Citation

Clark, C. AND T. Greaver. Implications of recent final and draft decisions to atmospheric deposition of N and S. USFS Monthly FARM Seminar, Washington, DC, March 13, 2024.