1. 1-Hour NO2 NAAQS Air
Quality Modeling
Dan Dix
All4 Inc.
NCASI 2011 Northern Regional
Wausau, WI
May 19, 2011

2. NO2 NAAQS
 Old Nitrogen Dioxide (NO2) NAAQS
• Annual: 100 µg/m3 (53 ppb) (Maximum
Annual Concentration)
 New NO2 NAAQS
• 1-Hour NAAQS: 188 µg/m3 (100 ppb) (3-Year
Average of the 98th Percentile of Daily
Maximum 1-hour Concentrations
 Annual NAAQS Still in Place
 Annual PSD Increment Still in Place
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3. NO2 Air Quality Modeling Requirements
 AERMOD
 188 µg/m3 (100 ppb): 5-Year Average of
the 98th Percentile of Daily Maximum 1-
hour Concentrations with National
Weather Service (NWS) Data
 188 µg/m3 (100 ppb): 98th Percentile of
Daily Maximum 1-hour Concentrations
with 1-year of Onsite Data
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4. PSD Air Quality Modeling Approach
 Model Project-Related Emissions for
comparison to:
 Significant Impact Levels (SILs)
 Annual - 1.0 g/m3 (Maximum Annual
Concentration)
 1-hour – 7.5 g/m3 (interim) (Maximum
Average Annual Concentration)
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5. PSD Air Quality Modeling Approach
 If Project-Related Emissions are Greater
than SIL, Multi-Source NAAQS analysis
required
 All Facility-Wide NO2 Emission Rates Must be
Modeled at their Potential-to-Emit Emission
Rate
 All Local Sources within 50km + Significant
Impact Area (SIA)
 Background Concentrations
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6. PSD Air Quality Modeling Approach
 Treatment of Intermittent Emission Units
 Emergency Generators
 Intermittent Emission Scenarios
(Startup/Shutdown)
 US. EPA Released in Latest Guidance
Memorandum
 Form of the Standard Does Not Warrant
Assuming Continuous Operation for Intermittent
Emissions (Case-by-Case Basis)
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7. Other Accepted NO2 AQM Techniques
 Tiering Approach for NO2 provided in
Latest Guidance Memorandum
 Tier I – Assume Full Conversion of NOX to
NO2 (1 g/m3 = 1 g/m3)
 Tier II – Use 0.8 as Default Ambient Ratio
(1 g/m3 = 0.8 g/m3)
 Tier III – Plume Volume Molar Ratio Method
(PVMRM) or Ozone Limiting Method (OLM)
 Will Become More Important to Collect
NO2/NOX In-stack Ratios from CEMS
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8. Other Accepted NO2 AQM Techniques
 Tiering Approach for Including Background
Concentrations provided in Latest
Guidance Memorandum
 Tier I – Add the Highest Hourly Background
Concentration to Modeling Concentration
 Tier II – Multi-Year Average of Background
Data by season and hour-of-day
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9. What Does All This Mean?
 Much more difficult to meet new standards
 Will need to consider shutting down sources or
controlling source.
 New guidance adds some flexibility for
assessing NO to NO2 chemistry
 New guidance adds some flexibility for
incorporating background concentrations
 New guidance on intermittent sources is very
important and benificial
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10. Recommendations
 If at all possible get below the SIL for PSD
project
 Complete exploratory NAAQS modeling to
determine current impacts for long range
planning at facilities (“What if” Scenarios)
 Watch out for
 Low wind speeds
 Distance to “property line”
 Impacts greater than plume can travel
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11. Questions?
Dan Dix
ddix@all4inc.com
All4 Inc.
2393 Kimberton Road
P.O. Box 299
Kimberton, PA 19442
610.933.5246 x18
www.all4inc.com
www.enviroreview.com
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