Cumulative Modeling Past and Present

Transcription

1 Cumulative Modeling Past and Present 1 James Thurman & Clint Tillerson U.S. EPA OAQPS/AQAD/AQMG 2018 Regional/State/Local Modelers Workshop Boston, MA thurman.james@epa.gov tillerson.clint@epa.gov

2 2 Overview Discuss cumulative modeling for SIPs and permitting and characterization of sources Modeling for SIPs and permitting differ from SO 2 designations modeling which allows for the use of input of actual emissions, i.e. CEMs, into the model Compare emissions inputs for modeled sources between 2005 and 2017 Guideline Illustrative examples

3 3 Cumulative modeling for SIPs and permitting Sources to model vs. representation in background When to model Source(s) being evaluated for an emissions limit (i.e., new/modify source or source with limit(s) included in SIP) Nearby sources Few sources that cause a significant concentration gradient When to represent in background Other sources that are adequately represented by monitored concentrations and not expected to cause a significant concentration gradient For more details, please see George Bridgers 2017 workshop presentation /2017/Presentations/1-19_2017_RSL-Cumulative_Impact_Analysis.pdf

4 Guideline For SIPs applications, sources taking a limit and modeled nearby sources treated essentially the same Source Emission limit Operating level Operating factor Source taking limit Maximum allowable emission limit or federally enforceable permit limit Actual or design capacity (whichever is greater) or federally enforceable permit condition* Continuous operation Nearby source Maximum allowable emission limit or federally enforceable permit limit Actual or design capacity (whichever is greater) or federally enforceable permit condition Continuous operation *For permitting: design capacity or federally enforceable permit condition

5 Guideline For SIPs and PSD applications, sources taking a limit and modeled nearby sources treated differently Nearby source can take into account actual operations when calculating operating level Allows representation of actual operating conditions by removing design capacity for nearby sources Source Emission limit Operating level Operating factor Source taking limit Maximum allowable emission limit or federally enforceable permit limit Actual or design capacity (whichever is greater) or federally enforceable permit condition Continuous operation Nearby source Maximum allowable emission limit or federally enforceable permit limit Temporally representative level when actually operating reflective of the most recent 2 years Continuous operation

6 Representation of sources in modeling Appendix W 2017 Appendix W Background source Nearby source Source taking limit Actuals Emissions representation Maximums (allowables x design capacity)

7 Appendix W 7 Source taking limit Nearby source Emission rate (g/s) Actual emissions (nearby source) Time (modeled period)

8 Example 1 8 Modeling under 2005 Guideline A B Monitor Model all sources at allowable emissions and design capacity or federally enforceable permit condition. No distinction between sources taking limits and those not taking limits. C D

9 Example 1 9 Flexibility under 2017 Guideline: Modeling of sources Scenario 1 Model as nearby source A B Model as source taking limit Monitor Model as nearby sources C D

10 Example 1 10 Flexibility under 2017 Guideline: Modeling of sources Scenario 2 Model as nearby source A B Model as source taking limit Monitor Treat as background sources C D

11 11 Example 2 F Modeling under 2005 Guideline A Model all sources at allowable emissions and design capacity or federally enforceable permit condition. No distinction between sources taking limits and those not taking limits. B C E Monitor D

12 12 Flexibility under 2017 Guideline: Modeling and background Scenario 1 Example 2 A Background sources F Background source Monitor B C E Model as nearby source D Model as source taking limit

13 13 Flexibility under 2017 Guideline: Modeling and background Scenario 2 Example 2 F Background source sector 1 A Monitor B Background sources sector 2 C E Model as nearby source D Model as source taking limit

14 14 Flexibility under 2017 Guideline: Modeling of sources Scenario 3 Example 2 A Model as nearby sources F Model as nearby source Monitor B C E Model as nearby source D Model as source taking limit

15 15 Flexibility under 2017 Guideline: Modeling of sources Scenario 4 Example 2 A Model as nearby sources F Model as nearby source Monitor B C E Model Model as as source nearby taking source limit D Model as source taking limit

16 16 Summary The 2017 update to Tables 8-1 and 8-2 of EPA s Guideline allow for more flexibility to appropriately characterize background concentrations as part of a cumulative modeling analysis. Under 2005 Guideline, model applications tended to be overly conservative by modeling most, if not all, sources within 50 km or nonattainment area at maximum allowable emissions (and often added monitored background too). Did not appropriately represent air quality concentrations with few implications under older NAAQS but did so under 1-hour NAAQS for SO2 and NO2 Under the 2017 Guideline, model applications are expected to more appropriately represent air quality concentrations within a nonattainment areas (for SIPs) and in proximity to new/modifying sources (for permits). This allows for a more realistic characterization of air quality to inform CAA programs.

17 17 Questions?