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Introduction

Using Maximum Wind Speed to Limit Off-Site Inventories for 1-Hour NAAQS Modeling James Boylan (GA EPD), Peter Courtney (GA EPD), Yan Huang (GA EPD), Leigh Bacon (ADEM), and Tom Rogers (FL DEP) 2012 EPA Region 4 Modelers Workshop November 14, 2012 – Atlanta, GA. Introduction.

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Introduction

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  1. Using Maximum Wind Speed to Limit Off-Site Inventories for1-Hour NAAQS ModelingJames Boylan (GA EPD), Peter Courtney (GA EPD), Yan Huang (GA EPD), Leigh Bacon (ADEM),and Tom Rogers (FL DEP)2012 EPA Region 4 Modelers WorkshopNovember 14, 2012 – Atlanta, GA

  2. Introduction • Since steady-state plume models do not inherently account for transport distance, there should be a limit to which sources are modeled together for determining a concentration associated with each hour. • Historically, we’ve included sources out to 50 km (and beyond) when the critical averaging times associated with the NAAQS were 24-hr or longer. • Now that the critical averaging time is1-hour, the default transport distance should be re-evaluated in light of the steady-state plume limitations.

  3. Plume Interaction How far from “A” would another source “B” need to be before the plumes from these sources would interact during the same one-hour time period? A B Wind = y km/hr Distance = x km The effluent from “A” emitted at the beginning of the 1-hour period travels y km in one hour. This effluent cannot combine with “B” during this same 1-hour period unless “B” is within y km of “A” (x < y). If not, then the two plumes cannot interact within that same hour.

  4. A Few Options to Consider • GA EPD • Use the maximum wind speed • Most conservative of three approaches • ADEM • Use the 99th percentile (SO2) wind speed for SO2 and the 98th percentile wind speed for NO2 • Same form as the 1-hour NAAQS • FL DEP • Use ADEM approach plus account for interaction time • Least conservative of three approaches, but might be most realistic

  5. GA EPD Example • Use the maximum 1-hour wind speed in the 5-year meteorological data set • 11.3 m/s  40.7 km max. transport distance • Can use this information to reduce the receptor grid and reduce the off-site emission inventory • Such a reduction does not eliminate the inclusion of sources outside this distance from the overall analysis since these sources will be accounted for in the background concentration.

  6. Refined 1-hr NO2 Modeling

  7. Refined 1-hr NO2 Modeling

  8. 1-hr SO2 Significance Modeling

  9. 1-hr SO2 Significance Modeling

  10. Max. Wind Speed by Sector

  11. 1-hr SO2 Significance Modeling

  12. GA EPD Summary • Refined 1-hr NO2 modeling • Reduced the number of receptors by 33% • 33,927 (50 km) to 22,889 (41 km) • When the 41-km grid is used for refined 1-hr NO2 modeling, no concentrations greater than the 1-hr NAAQS are identified. • Refined 1-hr SO2 modeling • Reduced the number of off-site sources assessed in the refined SO2 model by more than 50%.

  13. ADEM SO2 Travel Distance

  14. ADEM NO2 Travel Distance

  15. Interaction Time Interaction zone Overlap in same hour 1-Hour B A How much overlap of the two plumes is required to constitute a significant interaction (i.e., include both plumes in the same hour average)?

  16. FL DEP Example • Use the 99th percentile wind speed from Tampa to determine the maximum distance a plume could travel in one hour. • 7.82 m/s  28.2 km/hr • Thus, sources beyond 28.2 km would never interact within the same hour. • If some degree of interaction is considered, then the maximum distance is proportionately reduced by the fraction of overlap. • If 30 minutes of overlap is used (0.5 hour), the maximum distance would be 14.1 km.

  17. AECOM Study • “Short‐Range Model Distance Applicability Study” by Bob Paine (AECOM) at the 10th EPA Modeling Conference • Compared steady‐state model vs. non‐steady‐state model with constant meteorological conditions • Results suggest that a 20‐km limit seems more appropriate for steady‐state model (e.g., AERMOD) applicability rather than the current limit of 50 km • AERMOD should provide information to users regarding hourly plume travel time

  18. Contact Information Jim Boylan, Ph.D.Georgia Dept. of Natural Resources4244 International Parkway, Suite 120Atlanta, GA 30354James.Boylan@dnr.state.ga.us 404-362-4851

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