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APPENDIX C AIR QUALITY METHODOLOGY AND ASSUMPTIONS The CALlNE-4 model is a fourth-generation line source air quality model that is based on the Gaussian diffusion equation and employs a mixing zone concept to characterize pollutant dispersion over the roadway. Given source strength, meteorology, site geometry and site characteristics, the model predicts pollutant concentrations for receptors located within 150 meters of the roadway. The CALlNE-4 model allows roadways to be broken into multiple links that can vary in traffic volume, emission rates, height, width, etc. A screening-level form of the CALlNE-4 program was used to predict concentrations.1 Normalized concentrations for each roadway size (2 lanes, 4 lanes, etc.) are adjusted for the two-way traffic volume and emission factor. Calculations were made for a receptor at a corner of the intersection, located at the curb. Emission factors were derived from the California Air Resources Board EMFACl-2oo2 computer program based on a 2005 and 2030 Bay Area vehicle mix. The screening form of the CALI NE-4 model calculates the local contribution of nearby roads to the total concentration. The other contribution is the background level attributed to more distant traffic. The 1-hour background level in 2006 was taken as 3.8 PPM and the 8-hour background concentration was taken as 2.5 PPM. The 1-hour background level in 2010 was taken as 3.5 PPM and the 8-hour background concentration was taken as 2.3 PPM. These backgrounds were estimated using isopleth maps and correction factors developed by the Bay Area Air Quality Management District. Eight-hour concentrations were obtained from the 1-hour output of the CALlNE-4 model using a persistence factor of 0.7. Estimates of regional emissions generated by project traffic were made using a program called URBEMIS-2002.2 URBEMIS-2002 is a program that estimates the emissions that result from various land use development projects. Land use project can include residential uses such as single-family dwelling units, apartments and condominiums, and nonresidential uses such as shopping centers, office buildings, and industrial parks. URBEMIS-2002 contains default values for much of the information needed to calculate emissions. However, project-specific, user-supplied information can also be used when it is available. 1 Bay Area Air Quality Management District, BAAQMD CEQA Guidelines, 1996 (Revised 1999). 2 Jones and Stokes Associates, Software User's Guide: URBEMIS2002 for Windows with Enhanced Construction Module, Version 8.7, April 2005. Cl