1-Hour NO2 NAAQS Air Quality Modeling

NCASI 2011 Northern Regional

Wausau, WI

May 19, 2011

Dan DixAll4 Inc.

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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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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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Model Project-Related Emissions for comparison to: Significant Impact Levels (SILs)

Annual - 1.0 mg/m3 (Maximum Annual Concentration)

1-hour – 7.5 mg/m3 (interim) (Maximum Average Annual Concentration)

PSD Air Quality Modeling Approach

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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

PSD Air Quality Modeling Approach

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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)

PSD Air Quality Modeling Approach

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Other Accepted NO2 AQM Techniques

Tiering Approach for NO2 provided in Latest Guidance Memorandum Tier I – Assume Full Conversion of NOX to

NO2 (1mg/m3 = 1mg/m3) Tier II – Use 0.8 as Default Ambient

Ratio (1mg/m3 = 0.8 mg/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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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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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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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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Questions?

Dan Dix

ddix@all4inc.com

All4 Inc.2393 Kimberton Road

P.O. Box 299Kimberton, PA 19442

610.933.5246 x18

www.all4inc.com www.enviroreview.com