CT-EMFAC models on-road vehicle emissions for criteria pollutants, Mobile Source Air Toxics (MSATs) and carbon dioxide (CO2).  The tool's underlying emission factor information is based on the California Air Resources Board (CARB) EMFAC2007 on-road emissions model and the MSAT speciation factors provided by CARB.  The emission processes modeled by CT-EMFAC are: 
* Running exhaust - pollutants emitted from the tailpipe while vehicles are traveling;
* Running losses - evaporative emissions that occur during vehicle operation. 

EMFAC2007 provides emission factors for 13 vehicle classes (various types of cars, trucks, buses, and other vehicles).  As a default, CT-EMFAC uses composite fleet-average emission factors based on EMFAC2007 assumptions concerning the mix of the 13 vehicle classes operating in a given area.  However, for project analyses, CT-EMFAC users have the option of varying the fraction of the fleet that falls into the trucks and nontrucks categories.  In CT-EMFAC, medium-duty and larger vehicles are considered trucks; all other vehicles are considered nontrucks.  This distinction is based on EMFAC2007 classifications and on the fact that most project analysts consider medium-duty and larger vehicles to be trucks for transportation planning purposes.  

The medium-duty and larger vehicle fleet includes both gasoline and diesel-powered vehicles.  Therefore, when a CT-EMFAC user either selects the default fleet mix or defines the percent of the fleet equal to trucks, the truck percentage includes both gasoline and diesel-powered trucks.  The tool automatically apportions the truck fleet into appropriate diesel- and non-diesel fractions, based on EMFAC2007 data.  The tool then uses the diesel portion of the truck fleet to calculate diesel-related emissions such as diesel particulate matter.  

CT-EMFAC was first released in 2007 (Version 1.5).  Subsequent releases (Version 2.0, February 1, 2008; Version 2.6, May 29, 2008) improved calculation of diesel-related emissions and corrected a software problem related to modeling San Diego-area emissions.  Version 3.0 (February 19, 2010) added the ability to output diesel exhaust organic gas (DEOG) emissions.  Version 4.0 (March 26, 2010) added the ability to run multiple project scenarios in a batch mode.  This version (4.1) (September 20, 2010) adds the ability to work with an additional spreadsheet tool, "CT-EMFAC Naphthalene and POM Template.xls", to estimate naphthalene and polycyclic organic matter (POM) emissions.  Versions 3.0, 4.0, and 4.1 were prepared by Song Bai, Jeff Prouty, and Douglas Eisinger at Sonoma Technology, Inc. (STI), with permission from U.C. Davis.  Complete model documentation is available via Caltrans: http://www.dot.ca.gov/hq/env/air/pages/ctemfac_license.htm.