PM10 Modeling as Compliance with PM2.5

Did It Work?

History of PM2.5 Regulation

• 1997: - 24-hour: 3-year average of 98th percentile ≤ 65 µg/m3

- Annual: 3-year average ≤ 15 µg/m3

• Challenges lead to remand of PM2.5 standards

• 2006: - 24-hour: ≤ 35 µg/m3

- Annual: ≤ 15 µg/m3

OAQPS Memo – October 1997: “EPA believes that PM10 may properly be used as a surrogate for PM2.5 in meeting NSR requirements . . .”

Interim Implementation for Modeling PM2.5

“Meeting these measures in the interim will serve as a surrogate approach for Reducing PM2.5 emissions and protecting air quality.”

10 Years Later• Standard reduced• Inconsistent PM2.5/PM10 Emissions Relationship• PM2.5 Background Values closer to Standard than PM10• Still use PM10 as Surrogate and Permitting Away

Are We Protective of Air Quality?

Minor Source Case Studies

• PM10 and PM2.5 Modeling for Given Facility• Readily Available Emissions Factors• Background from Monitoring Sites with both PM10 and PM2.5

Study a Typical Hot Mix Asphalt Plant

Hot Mix Asphalt Plant Emissions Sources

• Drum Dryer Stack (Stack Filterable and Condensable)• Diesel Gen. Stack (Stack Filterable and Condensable) • Silo-Filling and Loadout (Condensable Fugitive)• Oil heater (Stack Filterable and Condensable)• Agg. Mat. Handling (Direct Fugitive)• Scalping Screen (Direct Fugitive)• Conveyor Transfers (Direct Fugitive)

• AP-42 Emissions Factors• Model fugitives as volume sources• Vary Some Fugitives by Wind Speed • Pocatello Surface Met Data with Boise Upper Air

• Flat Terrain

• Ambient Air at 150 m Radius from Center of Site

• Sources Separated by 10 - 20 Meters

PM10 and PM2.5 24-HourBackground Concentrations

• PM2.5: Use Maximum of 3-year Averages of 98th Percentile• PM10: Use Maximum of 4th Highest Values of 3-year Data Sets

• Boise: PM10 = 56 µg/m3 ; PM2.5 = 30.3 µg/m3

• Pinehurst: PM10 = 78 µg/m3; PM2.5 = 40.0 µg/m3

• Coeur d’Alene: PM10 = 58.0 µg/m3 ; PM2.5 = 29.3 µg/m3

• West of Pocatello: PM10 = 156 µg/m3 ; PM2.5 = 33.7 µg/m3

NAAQS Compliance Demonstration

PM2.5 = 29.8 µg/m3 + (29.3 µg/m3 to 40.0 µg/m3) = 59.1 µg/m3 to 69.8 µg/m3

PM10 = 50.0 µg/m3 + (56 µg/m3 to 156 µg/m3) = 106 µg/m3 to 206 µg/m3

169% to 199% of 35 µg/m3 Standard

71% to 137% of 150 µg/m3 Standard

Implications:

• Renewal of Tier II Permits may be Problematic

• Modifications Reveal Facility-Wide Issues

• Generic Permitting Programs may not Assure Compliance

• Fewer Sources will be Exemptible from Modeling Review