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4.1 – Air Quality Draft Environmental Impact Report February 2021 14800 W. Schulte Road Logistics Center 4.1-40 interface based on the California LINE Source Dispersion Model, which allows microscale CO concentrations to be estimated along each roadway corridor or near intersections (Caltrans 1998a). The emissions factor represents the weighted average emissions rate of the local County vehicle fleet expressed in grams per mile per vehicle. Consistent with the traffic scenario, emissions factors for 2022 were used. Emissions factors were predicted by EMFAC2017 based on a 5-mile-per-hour average speed for all of the intersections for approach and departure segments. The hourly traffic volume anticipated to travel on each link, in units of vehicles per hour, was based on information provided by the Traffic Impact Analysis and modeling assumptions are outlined in Appendix B. Four receptor locations were modeled at each intersection to determine CO ambient concentrations. A receptor was assumed on the sidewalk at each corner of the modeled intersections to represent the future possibility of extended outdoor exposure. CO concentrations were modeled at these locations to assess the maximum potential CO exposure that could occur in 2022. A receptor height of 5.9 feet (1.8 meters) was used in accordance with Caltrans recommendations for all receptor locations (Caltrans 1998b). The CO Protocol recommends using the highest 1 -hour measurement in the last 3 years as the projected future 1-hour CO background concentration for the analysis (Caltrans 2010). A CO concentration of 3 ppm by volume was recorded in 2018 for the Stockton monitoring station in San Joaquin County and was assumed in the California LINE Source Dispersion Model for 2022 (EP A 2020). To estimate an 8 -hour average CO concentration, a persistence factor of 0.69, as calculated based on the CO Protocol (Caltrans 2010), was applied to the output values of predicted concentrations in ppm at each of the receptor locations. Model inpu t and output data are available in Appendix B. Table 4.1-12 summarizes the maximum 1 -hour and 8-hour CO concentrations at the studied intersections. Table 4.1-12. CALINE4 Predicted Carbon Monoxide Concentrations Intersection Maximum Modeled Impact for Year 2022 Cumulative Plus Project (ppm) 1-Hour 8-Houra Hansen Road and Schulte Road 3.3 2.78 Valpico Road and Corral Hallow Road 3.4 2.87 Lammers Road and 11th Street 3.7 3.12 Source: Caltrans 1998a (CALINE4). Notes: ppm = parts per million See Appendix B. a 8-hour concentrations were obtained by multiplying the 1-hour concentration by a persistence factor of 0.69 (Caltrans 2010). As shown in Table 4.1 -12, the maximum CO concentration predicted for the 1 -hour averaging period at the studied intersections would be 3.7 ppm, which is below the 1 -hour CO CAAQS of 20 ppm (CARB 201 6c). The maximum predicted 8 -hour CO concentration of 3.12 ppm at the studied intersections would b e below the 8-hour CO CAAQS of 9.0 ppm (CARB 2018). Neither the 1 -hour nor 8-hour CAAQS would be equaled or exceeded at any of the intersections studied. Accordingly, the Project would not cause or contribute to violations of the CAAQS and would not result in exposure of sensitive receptors to localized high concentrations of CO. CO tends to be a localized impact associated with congested intersections. Thus, the Project’s CO emissions would not contribute to significant health effects associated with this pollutant. As such, impacts to sensitive receptors with regard to potential CO hotspots resulting from the Project’s contribution to cumulative traffic-related air quality impacts would be less than significant.