As previously mentioned, the CAL3QHCR model uses a full year of hourly meteorological data. Use of representative meteorological data that has been collected on-site is preferred; however, if on-site data is not available, National Weather Service (NWS) 110 data, representative of the area being modeled, is acceptable. If NWS data is used, the model must be run for five consecutive meteorological years. 111 

## E.2.6.4 Vehicular Emission Rates 

Vehicular emission rates are estimated for queuing and idling vehicles using the EPA -approved models: MOVES and California’s EMFAC. Emission rates for each idling and queuing link are input into the CAL3QHC/R model as gram per vehicle -mile and gram per vehicle -hour, respectively. Refer back to Section E.2.4 ( Estimate On-Road Vehicle Emissions ) for the steps on how to generate emission factors with MOVES and California’s EMFAC models. 

## E.2.7 Estimate Background Data 

Once the project-level emissions and dispersion modeling analysis is complete and pollutant concentrations associated with the project have been computed, representative background concentrations should be added to the predicted worst-case project-level concentration (for both CO and PM). Background concentrations are typically obtained from a background monitoring site not affected by the intersection (s) of interest. EPA’s AirData provides b ackground monitoring data at different monitoring locations collected across the U. S. for the seven criteria pollutants. 112 

The evaluation and selection of monitoring data for use in a particular analysis must follow the process defined in each area’s interagency consultation procedures. Background moni tored data should also be adjusted for future-year conditions. Methods used to compute future background concentrations for CO and PM hot-spot analyses are detailed in EPA’s Guideline for Modeling Carbon Monoxide from Roadway Intersection , and EPA’s Transportation Conformity Guidance for Quantitative Hot-spot Analyses in PM$_{2.5 }$and PM$_{10 }$Nonattainment and Maintenance Areas , respectively, mentioned above. 

