Modeling Guidance and Examples for Commonly Asked Questions (Part II)

1. Modeling Guidance and Examples for Commonly Asked Questions(Part II) Reece Parker and Justin Cherry, P.E. Air Permits Division Texas Commission on Environmental Quality Advanced Air Permitting Seminar 2014

2. What Is PM2.5? Direct Chemical Formation Stationary Sources NOx and SO2 PM2.5 The chemical composition of PM2.5 can vary with the local topography, source emissions, time of year, and weather.

3. PM2.5 Standards • NAAQS: • 24-hr: 35 µg/m3 • Primary Annual: 12 µg/m3 • Secondary Annual: 15 µg/m3 • Increments: • 24-hr: 9 µg/m3 • Annual: 4 µg/m3 • SIL*: • 24-hr: 1.2 µg/m3 • Annual: 0.3 µg/m3 *with sufficient justification

4. Using the SIL • PM2.5 SIL justification for NAAQS: • Determine a representative background value • Subtract the background from the NAAQS • Compare the difference to the SIL SIL Background Value NAAQS

5. 4 Assessment Cases Case 1: Direct PM2.5 < 10 tpy SER; NOx and/or SO2 < 40 tpy SER • Primary impacts only Case 2: Direct PM2.5≥ 10 tpy SER; NOx and/or SO2 < 40 tpy SER • Primary impacts, still must address secondary formation Case 3: Direct PM2.5≥ 10 tpy SER; NOx and/or SO2 ≥ 40 tpy SER • Primary impacts AND secondary impacts Case 4: Direct PM2.5 <10 tpy SER; NOx and/or SO2 ≥ 40 tpy SER • Primary impacts AND secondary impacts

6. Case 1 Direct PM2.5emissions < 10 tpy and SO2 and/or NOx emissions < 40 tpy: • Model direct PM2.5emissions following guidance for a NAAQS analysis

7. Case 2 Direct PM2.5emissions ≥ 10 tpy: • Model direct PM2.5emissions following guidance for a NAAQS analysis SO2 and/or NOx emissions < 40 tpy: • Discuss in AQA why proposed SO2and NOx emissions are not significant to the secondary formation of PM2.5

8. Case 3 Direct PM2.5emissions ≥ 10 tpy: • Model direct PM2.5emissions following guidance for a NAAQS analysis SO2 and/or NOx emissions > 40 tpy: • Provide a qualitative, hybrid qualitative/quantitative, or quantitative assessment of the secondary formation of PM2.5

9. Case 3 Qualitative Approach Ideas to consider: • Peak impacts from direct emissions and secondarily formed PM2.5likely do not overlap • Assessment of background data and condition with the NAAQS

10. Case 3 Qualitative Approach (Continued) Ideas to consider: • Evaluation of speciatedPM2.5 data: • Magnitude of secondary PM2.5precursor emissions from existing sources • Comparing project precursor emissions to those of existing sources • Limitations of chemical species necessary for photochemical reactions to form secondary PM2.5

11. Case 3 Hybrid Approach • Qualitative: Follow the Case 3 qualitative assessments • General conclusions from existing photochemical modeling

12. Case 3 Quantitative Approach • Quantitative #1: • Assume 100% conversion from SO2 and NOx to PM2.5 • Assess combined impacts of direct and equivalent direct PM2.5 emissions • Quantitative #2: • Full quantitative photochemical grid modeling exercise* *No requirement for photochemical modeling - this will be discussed further

13. Case 4 Direct PM2.5 emissions <10 tpy: • Model direct PM2.5 emissions following guidance for a NAAQS analysis SO2 and/or NOx emissions ≥40 tpy: • Provide a qualitative, hybrid qualitative/quantitative, or quantitative assessment of the secondary formation of PM2.5

14. Case 3 Example Direct PM2.5 emissions: 62 tpy NOx emissions: 96 tpy SO2 emissions: 10 tpy Need to address secondary formation of PM2.5.

15. Case 3 Qualitative Example • Slow transformation and small portions of NOx emissions can convert to PM2.5 • Maximum concentration areas for secondary impacts of NOx are not likely to overlap with direct impacts of PM2.5

16. Case 3 Example (Cont.) Qualitative (Cont.): • Speciated PM2.5 data shows nitrates make up 2% of total PM2.5 concentration • Regional NOx emissions have a magnitude of 25,000 tons • Project emissions of NOx (96 tpy) are small and not likely to contribute to secondary formation of PM2.5

17. Case 3 Example (Cont.) Quantitative: • Assume 100% conversion of NOx to (NH4)NO3 • Using NACAA formula: 1 µg/m3of NOx could form 1.7391 µg/m3 of (NH4)NO3 • 24-hr and annual NOxfrom the source predicted to be 2.9 µg/m3 and 0.3 µg/m3,respectively • Using the formula, 24-hr and annual secondary formation from the source would be 5µg/m3 and 0.5 µg/m3, respectively

18. Case 3 Example (Cont.) Quantitative (Cont.): • 24-hr and annual predicted concentrations from the direct emissions of PM2.5were 2 µg/m3 and 1µg/m3, respectively • Add all components together for a total value

19. PM2.5 Increment What to consider: • Major source baseline date - October 20, 2010 • Trigger date - October 20, 2011 • Minor source baseline date - county specific • SIL: • Additional justification • Output metric: • Yearly H1H vs. 5-year average

20. PM2.5 SIL Justification for Increment • Evaluate proposed direct PM2.5 emissions increases: • Report the maximum predictions and not a 5-year average • Provide justification for using the SILs to compare with the model predictions

21. PM2.5 SIL Justification for Increment

22. PM2.5 Monitoring for Increment 5 years of monitoring data (µg/m3): SIL Increment Consumed 2013-2010 Increment Standard

23. PM2.5 Increment When predictions are greater than the SIL or if the SIL cannot be justified: • Evaluate increment affecting sources together with the project sources • Document approach to identify increment affecting sources • Receptors - the extent of the receptor grid needs to capture maximum concentrations from the project and show that concentrations are decreasing

24. PM2.5Increment (continued) Further detail: • PSD major sources were further evaluated: • Projects with completion dates 18 months prior to the major source baseline date up to the minor source baseline date were identified • Projects were reviewed to determine if PM2.5 was associated with project • The extent of the modeling domain used to limit search for PSD major sources: • 24-hr and annual GLCmax locations, distance from property line, etc.

25. PM2.5Increment (continued)

26. Contact Information Justin Cherry • Reece Parker • Air Dispersion Modeling Team • (512) 239-1348 • reece.parker@tceq.texas.gov • Justin Cherry, P.E. • Air Dispersion Modeling Team • (512) 239-0955 • justin.cherry@tceq.texas.gov (512) 239-0955 justin.cherry@tceq.texas.gov Air Permits Division Reece Parker (512) 239-1348 reece.parker@tceq.texas.gov Air Permits Division