Agenda - Environmental Policy Board - 10/15/2018

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factors into account when generating emission rates. Average CO emission rates for 2002 and 2008 were generated using Mobile 5b. The ratio of the 2008 rate to the 2002 rate was used to decrease background CO concentrations by a factor of 0.91. Background traffic volume will increase from 2002 to 2008. This increase will in turn increase vehicle CO emission, which increases overall background CO concentrations. The ratio of the future regional traffic volume (2008) to the existing regional traffic volume (2002) was used to increase the background CO concentration by a factor of 1.34. These emission and traffic volume adjustment factors are summarized in Table 22.4. Table 22.4: Calculation of CO Background Concentrations Factor Maximum 2002 Monitored Concentration (ppm) Background Traffic Volume Adjustment Factor Emission Adjustment Factor _ Worst Case Background Concentration (ppm) State Standard (ppm) Federal Standard (ppm) Modeling Results 2008 1-Hour 8-Hour 2.1 1.34 0.91 2.56 30 35 1.4 1.34 0.91 1.71 9 9 The carbon monoxide modeling analysis was based on forecasted traffic volumes and signal timing under predicted 2008 P.M. peak traffic conditions. Locations of likely outdoor human activity next to the analyzed intersections were selected for air quality receptors. Receptor locations were sited within a 1,000-foot radius of the analyzed intersections and are depicted in Figure 22.3. The siting of carbon monoxide receptors was based on the likelihood of human outdoor activity occurring in excess of one hour. This is consistent with the MPCA's method of quantifying adverse air quality impacts based on hours of exposure. Locations chosen include gas station parking lots, entrances to offices and buildings, parks, and open space. Existing commercial buildings and retail stores along Highway 10 are located in close proximity to the road. Therefore, receptors were placed on all four corners of the intersections as depicted in Figure 22.3. These receptors represent the locations of the greatest potential exposure to vehicle CO emissions. A total of twenty receptor locations were selected. The results of the air quality analysis are presented in Tables 22.5 and 22.6. Table 22.5 lists the 2008 P.M. peak one -hour CO concentrations which were derived directly from the CAL3QHC dispersion model. The 2008 background concentrations were added to the model results to yield a total one -hour CO concentration in ppm for each receptor. The wind angle for the highest CO concentration is also included in the table. The highest one -hour CO concentration modeled was 11.4 ppm at Receptor 15 at the 22-5