Tips to Improve Model Results

Transcription

1 Tips to Improve Model Results 2019 Missouri Air Compliance Seminar Joseph Stolle, PE, Senior Environmental Engineer Wendy Vit, PE, Senior Environmental Engineer March 7, 2019

2 What is an Air Model? Used to ensure that the proposed source/modification will not cause a violation of the NAAQS or increment standards Dispersion modeling provides estimate of the ambient concentration at a future (or maximum) emission level Model the source first and compare to Significant Impact Levels (SILs) Must include background and nearby sources for NAAQS comparison Pollutant Averaging Period Class II Increment Standard PM 2.5 Annual 4 µg/m 3 PM hour 9 µg/m 3 PM 10 Annual 17 µg/m 3 PM hour 30 µg/m 3 SO 2 Annual 20 µg/m 3 SO 2 24-hour 91 µg/m 3 SO 2 3-hour 512 µg/m 3 NO 2 Annual 25 µg/m 3

3 How Does it Work? AERMOD-Steady-State Dispersion Model EPA s preferred near-field dispersion model Applicable to a wide range of regulatory modeling studies in all types of terrain

4 Is AERMOD Conservative? Use a real world test case to determine

5 Test Case Source Summary Use data from the Bowline Dataset Coal fired power plant in New York Hourly SO2 CEMS and monitor data at 2 locations for a full year On-site hourly wind and temperature data available Used by EPA for their AERMOD Validation Study Parameter SO 2 Emission Rate Stack Height Exhaust Temperature Stack Exit Velocity Stack Diameter Value lb/hr (each stack) 10,500 ton/year (total) 285 ft (both stacks) o F (225 o F Average) fpm (2600 fpm Average) 18.8 ft (both stacks)

6 Source SO 2 Emissions SO 2 Emissions (lb/hr) Parameter Stack 1 Stack 2 Minimum 0 0 Maximum Average St. Deviation

7 SO 2 Monitor Locations

8 Model/Monitor Paired Correlation (South Monitor) High Monitor-South Paired Correlation Units in µg/m 3 Parameter Monitor Model Maximum Average St. Deviation

9 Model/Monitor Paired Correlation (North Monitor) North Monitor Paired Correlation Units in µg/m 3 Parameter Monitor Model Maximum Average St. Deviation

10 Is AERMOD Conservative? The analysis is Very conservative-not Necessarily AERMOD Conservative Assumption for Design Value Analysis Assume all occur at the same time Peak Emission Rate Worst-Case Meteorology Maximum Impact from Nearby Sources Must consider all ambient locations

11 What Can You Do? Set Realistic Emission Limits Tip: Use a Monte-Carlo simulation to estimate the probability of achieving continuous compliance

12 What Can You Do? Use On-site Wind Measurements C = Q/u * C = Pollutant Concentration Q = Pollutant Emission Rate u = Wind Speed Pollutant concentration inversely proportional to wind speed Measure as close to the release height as practical

13 What Can You Do? Verify Surface Roughness Length Tip: Check the vectors used to define the surface roughness length for the worstcase wind directions

14 What Else Can You Do? Calculate site specific background concentrations using on-site monitor data Utilize stack flow/temperature data that corresponds to the scenario modeled

15 Conclusion AERMOD model give realistic results when run using realistic parameters Design Value Analyses very conservative We have control over some inputs

16 Contact Joe Stolle, PE, Senior Environmental Engineer Wendy Vit, PE, Senior Environmental Engineer