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EfJtimating CO Emissions Using MOBILE 5a model u.s. EPA's MOBILE 5a mobile source emission factor model was used to estimate CO emissions from the source. The input file was prepared using MPCA-approved default parameters. Emission factors were derived for a speed of 2.5 mph (for idling emissions) and speeds of 25, 30, 35 and 40 mph (corresponding to the typical free-flow traffic speeds observed at the most impacted intersections during the March 1997 traffic study). Printouts of the input and output files (Mobile5a.in and Mobile5a.out, respectively) are attached. Efltimating CO Concentrations Using CAL3QHC model The CAL3QHC highway air dispersion model was used to estimate downwind CO COJllcentrations at receptor sites adjacent to the two most impacted intersections within one- qu.arter of a mile of the proposed site (County Road B2 at Long Lake Road and County Rclad B2 at Cleveland Avenue). Buckground CO Concentrations &: agreed to by Mr. Innocent Eyoh of the MPCA, the background CO concentrations used in this study are based on those measured in a monitoring study performed by Interpoll Laboratories for the Centre Pointe Business Park EAW which is located approximately two miles north of the Gateway site. This study was conducted from December 31, 1996 through January 13, 1997 and reported maximum 1-hour and 8-hour average background CO cOJllcentrations of 2.2 and 1.6 ppm, respectively. In accordance with MPCA guidance, these 1997 background concentrations were adjusted to aC1count for advances in vehicle emissions control technology by using the ratio of the idling emission factors for the years 2001 and 1997 (predicted by the MOBILE 5a model). 2001 Idling Emission Factor = 189.61 g/mile 1997 Idling Emission Factor = 238.80 g/mile i.e., the CO background concentrations for the year 2001 are as follows: 1-hour: 8-hour: 2.2 ppm x (189.61/238.80) = 1.7 ppm 1.6 ppm x (189.61/238.80) = 1.3 ppm CAL3QHC Modeling CO receptors were placed around the two most impacted intersections and the CAL3QHC model was run once for each intersection using data from the traffic study. The traffic flows uSled in the model for the year 2001 are taken directly from the traffic analysis of Question 22 and include both the traffic generated by the Centre Pointe Business Development and the growth in background vehicular traffic. The latter was determined in the traffic study by aslmming a traffic growth rate of 3 percent per year between the years 1997 and 2001. Printouts of the input and output files for each intersection (Longlake.in and Longlake.out, and Clt~vland.in and Clevland.out respectively) are attached. The results are summarized in Table 23.1. 2362468 \48185-1IrMN 15