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

Localized Significance Thresholds – Modeling Parameters ISCST meteorology used Meteorological data from one of 35 sites nearest SRA or site specific data if available Plume depletion due to dry removal mechanisms

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

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

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

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