SIA = The distance from the facility of the farthest receptor greater than SIL.Background concentrations must be added to the modeled concentration from a representative ambient monitor to account for natural levels of background NO2 concentrations
March 1, 2011 Memorandum “Additional Clarification Regarding Application of Appendix W Modeling Guidance for the 1-hour NO2 NAAQS – Keep In Mind – Form of the standard is the multi-year average of the 98th percentile of the annual distribution of daily maximum 1-hour values)Consider number of days operating.Consider what other units are operating when this unit operates.Emergency Generators Test Runs (Exercising) May want to consider running during the day during better meteorological dispersion conditions
March 1, 2011 Memorandum “Additional Clarification Regarding Application of Appendix W Modeling Guidance for the 1-hour NO2 NAAQSNAAQS is NO2 – Emissions Calculated as NOX which is converted to NO2 in the atmosphere in the presence of background Ozone (O3).New Version of AERMOD set up to handle hour-of-day and seasonal ozone values.A lower NO2 in-stack ration means that there is more NO competing for Ozone to convert to NO2.
Tier I – Highest hourly background concentration from representative monitor from the 3 most recent years of available data.Tier II – 3rd highest value for seasons and hour-of-day and 8th highest value for hour-of-day only. (Last 3 years of available data)Temporal Pairing will not be accepted except on rare cases for isolated sources.New Version of AERMOD set up to handle adding in background concentrations as outline in guidance document.
Emergency Generators – unfavorable dispersioncharacteristics. (low stack height with the possibility of being affected by building downwash
AERMOD may not be the best option for predicting 1-hour impacts.
1-Hour NO2 NAAQS Air Quality Modeling
1-Hour NO2 NAAQS Air Quality Modeling Dan Dix All4 Inc. NCASI 2011 Northern Regional Wausau, WI May 19, 2011
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 Place2
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 Data3
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)4
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 Concentrations5
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)6
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 CEMS7
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-day8
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 benificial9
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 travel10
Questions? Dan Dix email@example.com All4 Inc. 2393 Kimberton Road P.O. Box 299 Kimberton, PA 19442 610.933.5246 x18 www.all4inc.com www.enviroreview.com11