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mile to grams per hour. The parameters and assumptions used in the Mobile 5b analysis <br />are summarized in Table 22.3. <br />Table 22.3 Mobile 5b Model Inputs <br />Parameter <br />Model Inputs <br />Analysis Year <br />Free Flow Speed <br />Idling Factor Speed <br />Cold Start Percentages <br />Hot Start Percentage <br />Traffic Mix <br />Temperature <br />Inspection/Maintenance Program <br />Oxygenated Fuel <br />Average Fuel Volatility <br />2002 (existing) 2008 (future) <br />35-mph for all roadways <br />2.5-mph for all roadways <br />20.6 % for all traffic <br />27.3 % for all traffic <br />MN Car Registration Distribution <br />January, 20°F <br />No <br />Yes <br />9.0 psi <br />Background Carbon Monoxide Concentrations <br />Background carbon monoxide concentrations are needed as a baseline to accurately <br />predict future CO concentrations that incorporate modeled vehicle related emissions. <br />These background concentrations are added to the model generated vehicle CO emissions <br />to determine compliance with national and state air quality standards. <br />The background (2002) carbon monoxide concentrations for the three intersections <br />analyzed were derived from the MPCA-monitored CO site at 6000 West Moore Lake <br />Road in Fridley, MN. Figure 22.2 shows the location of this site. In discussions with the <br />MPCA it was agreed that this site had background characteristics similar to the <br />intersections being modeled and would be a conservative representation of background <br />CO concentrations. <br />Carbon monoxide emissions are monitored daily at the Fridley site by the MPCA. In <br />2002, the maximum one -hour and eight -hour CO concentrations were 2.1 ppm and 1.4 <br />ppm respectively. In order to obtain the background concentration for 2008 (modeled <br />year), these 2002 concentrations were adjusted for increases in regional traffic volume <br />and reductions in vehicle emission rates. <br />Average CO emission rates in the region are expected to decrease due to improved <br />emission controls, turnover in vehicle fleet and cleaner burning fuel sources. Because <br />over 50 percent of the overall carbon monoxide concentrations in the metropolitan area <br />are due to vehicle related emissions, the reduction in vehicle emission rates will tend to <br />decrease the overall background CO concentrations. The Mobile 5b model takes these <br />22-4 <br />