From Open Energy Information

The Urban Emissions Model (URBEMIS) uses the ITE Trip Generation Rate Manual and the Air Resources Board’s (ARB) motor vehicle emissions model (EMFAC) for transportation calculations. Area source outputs include natural gas use, landscaping equipment, and fireplaces. It also estimates construction impacts and impacts of mitigation options. An updated version with CO2 outputs will be available soon. In the interim, CO2 factors (pounds per mile) provided by ARB could be used to convert VMT per day into CO2 per day.