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Grand Avenue Widening Project Environmental Impact Report Section 3.0 • 24.75 tons of CO (550 pounds per day) • 2.5 tons of ROG (75 pounds per day) • 2.5 tons of N% (100 pounds per day) • 6.75 tons PM10 (150 pounds per day) • 6.75 tons of SO, (150 pounds per day) 3.4.3 METHODOLOGY RELATED TO AIR QUALITY CO is the pollutant of major concern along roads because the most notable source of CO is motor vehicles. As a result, CO concentrations are usually indicative of local air quality generated by a road network and are used as an indicator of the potential impacts of a road on local air quality. Local air quality impacts can also be assessed by comparing future CO concentration with the state and federal CO standards and by comparing future CO concentrations with and without a proposed project. Future CO concentrations in the Grand Avenue area, with and without the proposed widening, were forecast using the CALINE4 computer model. This model forecasts air quality impacts near transportation facilities, in the microscale region. Worst case meteorology was assessed. A late afternoon winter period with a ground based inversion was considered. For worst case meteorological conditions, a wind speed of 0.5 meter per second (one mile per hour) and a stability class G were used for a one hour averaging time. Stability class G is the worst case scenario in terms of the most turbulent atmospheric conditions. A worst case wind direction for each site was determined by the CALINE4 model. A sigma theta of 10 degrees was used to represent the fluctuation of wind direction. A high sigma theta value would represent a very changeable wind direction. The temperature used for worst case was 50 degrees F. Temperature affects the dispersion pattern and emission rates of motor vehicles. The temperature represents the January mean minimum temperature as reported by Caltrans. The wind speed, stability class, sigma theta and temperature data used for the modeling are those recommended in the Development of Worst Case Meteorology Criteria (California Department of Transportation, June 1989). A mixing height . of 1,000 meters was used as recommended in the CALINE4 Manual. A surface roughness of the ground in the area, 100 centimeters, was used based on the CALINE4 Manual. The results are also determined based on the LOS on the area roads. Emission factors for the arterials used with the CALINE4 computer model were obtained from the CARB. The emission factors of version MVEI7G, which is the latest version, were used. The CALINE4 modeling for the arterials was conducted using peak hour traffic data and includes traffic on Interstate 5 (I-5). The peak hour traffic for I-5 is assumed to be about ten percent of the average daily traffic on this freeway. Future projected traffic volumes with and without the proposed Grand Avenue widening project are essentially similar. F: WW-ENMGrand eirlNew Text - GrandlSection 3 SplitlSection 3.4.doc Page 3.4-8