Indirect Source Models

Two models used for indirect source modeling are Mobile 6.2 and CAL 3QHC. Mobile 6.2 generates vehicular carbon monoxide emissions that are then used by CAL3QHC to predict a carbon monoxide concentration at a receptor site.

Mobile 6.2

The Mobile 6.2 model has many different user options. Default values are generally used by the DNR to generate emission data. The Inspection/Maintenance records are only applicable for projects located in Milwaukee, Ozaukee, Kenosha, Racine, Waukesha, Sheboygan and Washington counties.

Mobile 6.2 will give results for each scenario listed in an input file. The emission factor results created are associated with the build year or the build year + 10 years. Mobile 6.2 cannot calculate idle emissions from vehicles to support the idle emission factor needed for input into the CAL3QHC model. Air Management multiplies the emission factor for 2.5 mph by 2.5 to derive an idle emissions estimate.

CAL3QHC

This model accepts a variety of user input. Only worst-case (or approved site specific ) input should be used.

Results of the CAL3QHC model show maximum concentrations for each receptor at each wind angle. The results from the 1 hour build and +10 year build scenarios should include the carbon monoxide background concentration. For hourly concentrations based on peak-hour traffic volumes, the value determined by the model over a 60 minute period is used, plus the ambient concentration to assess the total impact. There are four variables that need to be considered:

• Meteorological parameters-use the following default parameters

1. Wind speed-1.0 m/sec
2. Wind direction-gien in 5 or 10 degree increments over a 360 degree field
3. Stability class-E (5)
4. Ambient Temperature-20 degrees Fahrenheit
5. Mixing Height-1000 meters

• Traffic variables-peak and 8-hour averages per approach and lane, turn percentages, signal timing, parking lot capacity, and speed limits.
• Receptor placement-Receptors should be placed near sites where the maximum concentration is most likely to occur, when the traffic will be the most congested and where the public has continuous access. Receptors should be located at the nearest opening (window, door) of the closest building to the intersection in each quadrant. If no building is present, place the receptor at the roadway right-of-way. The receptor height should be set at 1.8 meters, plus or minus the difference between and that of the receptor site, as the height of all receptors used in the modeling.
• Background cocentrations-Call DNR for latest background concentrations.