modeling guidance and examples for commonly asked questions (part ii)
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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. What Is PM 2.5 ?. Direct. Chemical Formation. Stationary Sources. - PowerPoint PPT PresentationTRANSCRIPT
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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
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What Is PM2.5?
NOx and SO2Stationary Sources
PM2.5
Direct Chemical Formation
The chemical composition of PM2.5 can vary with the local topography, source emissions, time of year, and weather.
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PM2.5 StandardsNAAQS:
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
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Using the SILPM2.5 SIL justification for NAAQS:
Determine a representative background value
Subtract the background from the NAAQS
Compare the difference to the SIL
Background Value SILNAAQS
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4 Assessment CasesCase 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
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Case 1Direct PM2.5 emissions < 10 tpy and SO2 and/or NOx
emissions < 40 tpy:Model direct PM2.5 emissions following guidance for a
NAAQS analysis
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Case 2Direct PM2.5 emissions ≥ 10 tpy:
Model direct PM2.5 emissions following guidance for a NAAQS analysis
SO2 and/or NOx emissions < 40 tpy:
Discuss in AQA why proposed SO2 and NOx emissions are not significant to the secondary formation of PM2.5
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Case 3Direct 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
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Case 3 Qualitative ApproachIdeas to consider:Peak impacts from direct
emissions and secondarily formed PM2.5 likely do not overlap
Assessment of background data and condition with the NAAQS
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Case 3 Qualitative Approach (Continued)Ideas to consider:Evaluation of speciated PM2.5 data:
Magnitude of secondary PM2.5 precursor 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
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Case 3 Hybrid ApproachQualitative: Follow the Case 3 qualitative assessments
General conclusions from existing photochemical modeling
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Case 3 Quantitative ApproachQuantitative #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
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Case 4Direct 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
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Case 3 ExampleDirect PM2.5 emissions: 62 tpy
NOx emissions: 96 tpy
SO2 emissions: 10 tpy
Need to address secondary formation of PM2.5.
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Case 3 Qualitative ExampleSlow 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
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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
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Case 3 Example (Cont.)Quantitative:
Assume 100% conversion of NOx to (NH4)NO3
Using NACAA formula: 1 µg/m3 of NOx could form 1.7391 µg/m3 of (NH4)NO3
24-hr and annual NOx from 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 5 µg/m3 and 0.5 µg/m3, respectively
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Case 3 Example (Cont.)Quantitative (Cont.):
24-hr and annual predicted concentrations from the direct emissions of PM2.5 were 2 µg/m3 and 1 µg/m3, respectively
Add all components together for a total value
Pollutant
Averaging Time
Project GLCmax (µg/m3)
Secondary Formation
from Project (µg/m3)
Background
(µg/m3)
Total Predicted
Concentration
(µg/m3)
NAAQS
PM2.5 24-hr 2 5 26 33 35
PM2.5 Annual 1 0.5 9.6 11.1 12
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PM2.5 Increment
What to consider:Major source baseline date - October 20, 2010Trigger date - October 20, 2011Minor source baseline date - county specific
SIL:Additional justification
Output metric:Yearly H1H vs. 5-year average
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PM2.5 SIL Justification for IncrementEvaluate 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
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PM2.5 SIL Justification for Increment
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PM2.5 Monitoring for Increment5 years of monitoring data (µg/m3):
24-hrConcentratio
ns
2009 2010 2011 2012 2013
H1H 23.4 23.2 22.9 23.5 23.3
H2H 21.9 22.1 21.4 22.3 22.9
Increment Consumed 2013-2010
SILIncrement Standard
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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
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PM2.5 Increment (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.
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PM2.5 Increment (continued)
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Contact InformationReece Parker
Air Dispersion Modeling Team (512) 239-1348 [email protected]
Justin Cherry, P.E.Air Dispersion Modeling Team (512) 239-0955 [email protected]
Air Permits Division
Reece Parker
(512) 239-1348
Air Permits Division
(512) [email protected]
Justin Cherry