1. Sunil Kumar TAC, COG July 9, 2007
Finding of Significant PM2.5 Precursors for SIP and Conformity Analysis Washington DC-MD-VA PM2.5 NAA
Sunil Kumar
TAC, COG
July 9, 2007

2. Washington DC-MD-VA PM2.5 NAA

3. Significant Precursors: Two-stage Process
Determine PM2.5 Precursors for SIP
Base Year inventory must include all precursors (PM10, PM2.5, NOx, SO2, NH3, VOC) in emissions inventory
SIP: Focus on significant precursors
NEXT, Determine PM2.5 Precursors for Mobile Budgets/Conformity

4. Evidence for Finding of Significance for Plan

5. PM2.5 Composition – STN Data McMillan (Washington, DC) - 2004

6. PM2.5 Composition – High Level Days McMillan (Washington, DC) - 2001-2003
Winter
Spring
Summer
Fall

7. PM2.5 Precursors for SIP Planning
PM2.5-Pri, SO2, NOx – Presumed significant by EPA
VOC & NH3 - Presumed insignificant by EPA
OC: Part of PM2.5-Pri emissions. Some OC also indirectly formed in the atmosphere due to VOC reactions (pathway not very well understood).
PM2.5-Pri, SO2, and NOx – Role in PM2.5 formation well established. EPA considers these pollutants to be significant PM2.5 precursors.
Basis of significance or insignificance: - Role in organic & elemental carbon, sulfate, & nitrate formation - Main constituents of PM2.5

8. PM2.5 Precursors for SIP Planning
VOC –
EPA presumes insignificant. Role of VOC varies by region and is not well understood yet.
NH3 –
Limited control options
Uncertainties in inventories
NH3 reduction increases precipitation acidity (ecological & health hazard)
After SO2 reduction, PM2.5 more responsive to NOx reduction than NH3.
VOC – High molecular weight VOC are direct organic carbon particle emissions. Role of VOC in the formation of secondary organic aerosol variable (area, local emissions sources, atmospheric chemistry, season) and is also the lest understood component of PM2.5 formation.
EPA presumes VOC as insignificant. States need to demonstrate through detailed technical analyses including sensitivity modeling its significance if they want it as a precursor.
NH3 – Reacts with sulfuric acid and nitric acid to form ammonium sulfate (both summer & winter) and ammonium nitrate (mainly in winter) respectively. Reducing SO2 reduces sulfate formation and therefore overall PM2.5 levels considerably. In areas with high SO2 emissions, ammonia reductions may marginally reduce PM2.5 concentrations, but particle and precipitation acidity may increase. Increased acidity is linked to adverse ecological and human health effects and with an increase in the formation of secondary organic compounds.
Limited control options.
Uncertainties in emission inventories. Improvements through process-based inventory approaches for animal feeding operations being looked into.
Monitoring of ammonia gas and nitric acid is important for identifying when PM2.5 formation in an area is limited by ammonia or by nitric acid. However, there are a limited number of such monitoring sites.
After substantial SO2 reductions in the east, in general PM2.5 changes are predicted to be less responsive to reductions in ammonia than to reductions in nitric acid.

9. Detailed technical analyses needed to prove VOC & NH3 significant
Photochemical modeling – zero-out analysis; sensitivity analysis
Photochemical source apportionment tools (PSAT, DDM, TSSA, etc.) for estimating impact of all sources
Receptor modeling (e.g. PMF, CMB)
Have
Analysis of ambient monitoring data, speciation data, and trends
Analysis of emissions inventories and trends

10. Recommendation PM2.5 Precursors for SIP Planning
Limited timeline to submit Annual PM2.5 SIP
Limited time/resources for modeling
Follow EPA’s recommendation – Consider PM2.5, SO2 and NOx as significant in absence of modeling

11. Significance Test for Conformity

12. PM2.5 Precursors for Conformity Analysis
PM2.5-Pri and NOx - Mobile budgets needed (Conformity rule).
SO2 - Need to demonstrate significant contribution from mobile sources and also look at other criteria for setting up mobile budget.
VOC & NH3 – If found significant for PM2.5 SIP, then need to look at contribution from mobile sources and other criteria for setting up mobile budget.

13. Checklist PM2.5 Precursors for Conformity Analysis

14. Checklist PM2.5 Precursors for Conformity Analysis