1. SCAQMD Modeling Parameters for Developing Localized Significance Thresholds March 5, 2003

2. 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

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

4. Localized Significance Thresholds – Modeling Parameters Receptors H Developed from 10 degree increments H 25, 50, 100, 200, 500 meter criteria pollutant receptor distances from source/site boundary H Receptors at breathing height H Flat terrain

5. Localized Significance Thresholds – Modeling Parameters Conservative H Background based on a rolling 3-year highest concentration observed at gaseous criteria pollutant monitoring sites

6. Localized Significance Thresholds – Modeling Parameters Uncertainties H ISCST3 - Gaussian probability distribution H Model based on uniform emission across site H Model based on 8-hour working day between 8 a.m. to 4 p.m. H Release height assumes day time conditions H Assumed all sources were stationary H Gradual NOx to NO 2 conversion H DRI PM decay factor