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concentrations.2 The intersection mode of the screening model was <br /> employed, which superimposes the worst case concentrations of the <br /> two intersecting roadways. Normalized concentrations for each <br /> roadway size (2 lanes, 4 lanes, etc. ) are adjusted for the two-way <br /> traffic volume and emission factor. Calculations were made for a <br /> receptor at the curbline. <br /> Emission factors were derived from the California Air Resources <br /> Board EMFAC-7EPSCF2 computer model. Emission rates were based on <br /> an average vehicle speed of 15 MPH. <br /> The screening model calculates the local contribution of nearby <br /> roads to the total concentration. The other contribution is the <br /> background level attributed to more distant traffic. The 1-hour <br /> background level was taken as 5.0 PPM for all analysis years. To <br /> calculate 8-hour concentrations from the 1-hour output of the <br /> CALINE-4 model, a persistence factor of 0.7 was employed. <br /> URBEMIS-3 PROGRAM <br /> Estimates of regional emissions generated by project employee <br /> traffic were made using a program called URBEMIS-3 . URBEMIS-3 is <br /> a program that estimates the emissions that would result from <br /> various land use development projects. Land use project can <br /> include residential uses such as single-family dwelling units, <br /> apartments and condominiums, and nonresidential uses such as <br /> shopping centers, office buildings, and industrial parks. <br /> URBEMIS-3 contains default values for much of the information <br /> needed to calculate emissions. However, project-specific, user- <br /> supplied information can also be used when it is available. <br /> The following is a description of the parameters that were used in <br /> the regional air- quality analysis of the proposed project: <br /> -Ambient Temperature: 75 degrees F. <br /> -Trip Lengths: <br /> Work: 10.6 miles <br /> Non-work: 9.0 miles <br /> The above trip lengths represent typical trip lengths for rural <br /> areas in California. Each employee was assumed to generate 2 .5 <br /> daily trips. <br /> An adjustment was made to the URBEMIS-3 output. The URBEMIS-3 <br /> program generates estimates of Total Organic Gases rather than <br /> Reactive organic Gases. Reactive organic Gases were assumed to <br /> equal 910 of the Total Organic Gases. <br /> 2 Bay Area Air Quality Management District, Air -Quallty and <br /> Urban --Guidelines, November 1985, Revised 1991. <br /> G-2 <br />