What is an Emission Factor? An emission factor is a rate at which pollution is generated by an on-road source. Reported in grams/mile. Vary by on-road source type and speed. Generated by the EPA MOBILE6 model.
What is an on-road source? MOBILE6 can model 28 vehicle classes:
What is the MOBILE6 model? The latest version of the EPA on-road emissions program (MOBILE6.2) Tool for predicting volatile organic compound (VOC), carbon monoxide (CO), and nitrogen oxide (NOx) emissions Used for State Implementation Plans (SIPs) and Conformity Required for use in all states but California
What factors go into MOBILE6? Model year – impacted by federal engine standards Gasoline content – oxygenates, sulfur, vapor pressure Control programs – Inspection and Maintenance Driving conditions – roadway, speed, air conditioning Environment – temperature, humidity Roadway type – freeway, arterial, ramp, local
What factors does MOBILE6 calculate? Combustion – VOC, NOx, CO - Running exhaust - Start emissions Evaporative – VOC - resting: hot soak, diurnal, resting losses - running: crankcase, running losses
How does MOBILE6 represent local conditions? Through the use of local data inputs: Registration distribution Vehicle Miles of Travel (VMT) Mix Local travel data Local control programs (I/M, anti- tampering programs) Local atmospheric data Diesel fractions
What do these emission factors look like? Vehicle Type: LDGV Year: 2007 Speed: 25 mph Composite Emission Factors (g/mi): Composite VOC : Composite CO : 6.18 Composite NOX :
So where is the problem? The number of miles driven. Example: composite NOx EF = 1.4 g/mile 134 million miles of travel per day = 187,600,000 grams per day = 206 tons of NOx per day 2007 On-Road Budget in the SIP NOx: tons per day VOC: tons per day
How do emission factors become an emission inventory? Emission factors are generated for: Each hour, each county, all speeds, all vehicle categories, all roadway types These are combined with the VMT data out of the Travel Demand model, resulting in emissions by: County, roadway, pollutant, and hour
What else can MOBILE6 do? MOBILE6.2 can also model: Toxics. This category includes certain metals, particulates, and organic compounds. Particulate matter, both PM10 and PM2.5. Carbon Dioxide, a greenhouse gas.