SCAQMD Modeling Parameters for Developing Localized Significance Thresholds

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SCAQMD Modeling Parameters for Developing
Localized Significance Thresholds

• March 5, 2003

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Localized Significance Thresholds Modeling
Parameters

• ISCST3
• 1981 meteorology used
• Meteorological data from one of 35 sites nearest
  SRA or site specific data if available
• Plume depletion due to dry removal mechanisms

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Localized Significance Thresholds Modeling
Parameters (Cont.)

• Source
• Stationary source approach
• Developed for 1, 2, and 5 acre sites
• Side by side elevated gaseous volume sources
• Area source for PM
• Emissions over 8-hr period (8 a.m. to 4 p.m.)
• Uniform emissions from area/volume sources
• 5 meter gaseous /1 meter PM release height

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Localized Significance Thresholds Modeling
Parameters

• Receptors
• Developed from 10 degree increments
• 25, 50, 100, 200, 500 meter criteria pollutant
  receptor distances from source/site boundary
• Receptors at breathing height
• Flat terrain

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Localized Significance Thresholds Modeling
Parameters

• Conservative
• Background based on a rolling 3-year highest
  concentration observed at gaseous criteria
  pollutant monitoring sites

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Localized Significance Thresholds Modeling
Parameters

• Uncertainties
• ISCST3 - Gaussian probability distribution
• Model based on uniform emission across site
• Model based on 8-hour working day between8 a.m.
  to 4 p.m.
• Release height assumes day time conditions
• Assumed all sources were stationary
• Gradual NOx to NO2 conversion
• DRI PM decay factor