Idling Vehicle Emissions for Passenger Cars, Light-Duty Trucks, and Heavy- Duty Trucks The amount of pollution that a vehicle emits is dependent on many factors. The U.S. Environmental Protection Agency (EPA) has developed a series of computer models that estimate the average emis- sions for different types of highway vehicles. This fact sheet is one of a series on highway vehicle emission factors. It presents average emis- sion rates for passenger cars, light-duty trucks, (e.g., pickup trucks, sport-utility vehicles), heavy-duty trucks (semi tractor-trailers), and motorcycles when they are idling. I-L. Introduction There are a number of factors that affect the rate at which any vehicle emits air pol' lutants, whether the vehicle is being driven or is at idle (engine running, but vehicle not moving). Some of the most important are: • vehicle type/size (passenger cars, light-duty trucks, heavy-duty trucks, motor- cycles) • vehicle age and accumulated mileage • fuel used (gasoline, diesel, others) • ambient weather conditions (temperature, precipitation, wind) • maintenance condition of the vehicle (well maintained, in need of maintenance, presence and condition of pollution control equipment) The most current version of the computer model that EPA uses to estimate average in-use emissions from highway vehicles is MOBILE6.2. EPA, the States, and others use this model to estimate total emissions of pollutants generated by highway vehicles in various geographic areas and over specific time periods. The idle emission rates or "emission factors" presented in this fact sheet are based on national data representing the in-use fleet as of July 2008, United States Environmental Protection Agency Office of Transportation and Air Quality EPA420-F-08-025 October 2008 ------- The emission rates of hydrocarbons (both volatile organic compounds [VOCs] and Total Hydrocarbons [THC]), carbon monoxide (CO), and nitrogen oxides (NOx) for idling vehicles are presented in the follow' ing tables. In addition, the emission rates of particulate matter (PM1C and PM ,) are provided for heavy- CO: g/hr: g/min: GVW: Ib: NOx: PM, 10- PM 2.5' ppm: psi: RVP: THC: VMT: VOC: Abbreviations and Acronyms Used Carbon monoxide; a regulated pollutant Carbon dioxide; the primary byproduct of all fossil fuel combustion gram(s) grams per hour grams per minute Gross Vehicle Weight pound Nitrogen oxides; a regulated pollutant Particulate matter under 10 microns diameter; a regulated pollutant Particulate matter under 2.5 microns diameter, sometimes referred to as "fine particulate" parts per million pounds per square inch Reid vapor pressure; a standardized method for expressing the volatility, or tendency to evaporate, of gasoline Total hydrocarbons Vehicle miles traveled Volatile organic compounds; equivalent to THC plus aldehydes minus both methane and ethane duty diesel vehicles only because the MOBILE model does not include PM for the other vehicle categories dur- ing idle operation. 1 These emission factors assume an "average" properly maintained vehicle, operating on typical gasoline or diesel fuel, on a warm summer day. Emission rates can be higher in very hot weather (especially HC) or in very cold weather (especially CO), National average values are used for registration distributions by age (what fraction of all cars, or light trucks, in use today are of the cur- rent model year, are one to two years old, 2 to 3 years old, and so forth up to 25 years old) and annual mileage accumulation rates by age (newer vehicles tend to be driven more miles per year than do older vehicles). Some of the other primary assumptions incorporated in these emission factors are: Ambient temperatures: Nominal gasoline volatility: Weathered fuel volatility: Gasoline sulfur content: Diesel sulfur content: Inspection/maintenance program: Reformulated gasoline: 72 to 92 °F day time range 9.0 psi Reid vapor pressure (RVP) 8.6 psi RVP 30 ppm 330 ppm No No Note that these emission rates are applicable for relatively short periods of idle time, as observed in drive-thru lanes, at toll gates, at stop lights, and in very heavily congested traffic. These idle emission rates are not applicable to "hoteling" situations for heavy-duty diesel trucks, where the truck engine may be idling for periods of hours at a time with many accessories being oper- ated from the engine power. EPA is currently studying the issue of emissions from heavy-duty ------- diesel trucks during "hoteling" situations; more information on this subject is available on EPA's SmartWay Transport Partnership Program web site at: www.epa.gov/smartway/idling.htm. These emission rates also are not applicable for buses (urban transit buses and school buses). Average idle emission estimates for urban and school buses are provided in the fact sheet "Average In-Use Emission Factors for Urban Buses and School Buses" (EPA420'F'08'026), Idle Emission Rates The following tables present idle emission factors expressed as grams per hour (g/hr) and grams per minute (g/min) of idle time. Table 1 presents idling emission rates for gasoline-fueled and diesel cars, light-duty trucks, and heavy-duty vehicles, and motorcycles. Definitions of Vehicle Types (Gross Vehicle Weight) LDGV: Light-duty gasoline-fueled vehicles, up to 6000 Ib GVW (gasoline-fueled passenger cars) LDGT: Light-duty gasoline-fueled trucks, up to 8500 Ib GVW (includes pick-up trucks, minivans, passenger vans, sport-utility vehicles, etc.) HDGV Heavy-duty gasoline-fueled vehicles, over 8500 Ib GVW (gasoline-fueled heavy-duty trucks) LDDV Light-duty diesel vehicles, up to 6000 Ib GVW (diesel engine passenger cars) LDDT: Light-duty diesel trucks, up to 8500 Ib GVW (diesel engine light-duty trucks) HDDV Heavy-duty diesel vehicles, over 8500 Ib GVW (diesel engine heavy-duty trucks) MC: Motorcycles (only those certified for highway use; all are gasoline-fueled) ------- The HDDV column represents the average of all diesel engine vehicles over 8,500 Ib gross ve- hicle weight (GVW); this category is dominated by the heaviest HDDVs (GVW Classes Villa and VHIb) which exceed 33,000 Ib GVW. Table 1: Average Idle Emission Rates by Pollutant and Vehicle Type2 Pollutant VOC THC CO NOx PM25 PM:o Units g/hr g/min g/hr g/min g/hr g/min g/hr g/min g/hr g/min g/hr g/min LDGV 2.683 0.045 3.163 0.053 71.225 1.187 3.515 0.059 N/A1 N/A1 N/A1 N/A1 LDGT 4.043 0.067 4.838 0.081 72.725 1.212 4.065 0.068 N/A1 N/A1 N/A1 N/A1 HDGV 6.495 0.108 7.260 0.121 151.900 2.532 5.330 0.089 N/A1 N/A1 N/A1 N/A1 LDDV 1.373 0.023 1.353 0.023 7.018 0.117 2.690 0.045 N/A1 N/A1 N/A1 N/A1 LDDT 2.720 0.045 2.680 0.045 5.853 0.098 3.705 0.062 N/A1 N/A1 N/A1 N/A1 HDDV 3.455 0.058 3.503 0.058 25.628 0.427 33.763 0.563 1.100 0.018 1.196 0.020 MC 19.153 0.319 21.115 0.352 301.075 5.018 1.625 0.027 N/A1 N/A1 N/A1 N/A1 Table 2 presents HDDV idle emission rates by weight class. The GVW weight classes are: Heavy-Duty Diesel Vehicle Classifications (Gross Vehicle Weight) lib: 8,501-10,000 Ib (e.g., full-size pick-up trucks, very large passenger vans) III: 10,001-14,000 Ib (e.g., panel trucks, small enclosed delivery trucks) IV: 14,001-16,000 Ib (e.g., city delivery trucks, landscape utility trucks) V 16,001-19,500 Ib (e.g., bucket utility trucks, large walk-in delivery trucks) VI: 19,501-26,000 Ib (e.g., rack trucks, single axle vans) VII: 26,001-33,000 Ib (e.g., tow trucks, garbage collection trucks) Villa: 33,001-60,000 Ib (e.g., long-haul semi-tractor trailer rigs) VHIb: > 60,000 Ib (e.g., long-haul semi-tractor trailer rigs) ------- Table 2: Average Idle Emission Rates for Heavy-Duty Diesel Vehicles by GVW Class3 Pollutant voc THC CO NOx PM25 PM10 Units g/hr g/min g/hr g/min g/hr g/min g/hr g/min g/hr g/min g/hr g/min lib 1.465 0.024 1.498 0.025 9.305 0.155 12.668 0.211 1.103 0.018 1.199 0.020 III 1.555 0.026 1.580 0.026 10.068 0.168 13.530 0.226 1.010 0.017 1.098 0.018 IV 2.025 0.034 2.055 0.034 12.898 0.215 17.850 0.298 1.065 0.018 1.157 0.019 V 2.120 0.035 2.150 0.036 13.183 0.220 18.655 0.311 1.008 0.017 1.095 0.018 VI 2.820 0.047 2.865 0.048 15.163 0.253 24.325 0.405 1.069 0.018 1.162 0.019 VII 3.503 0.058 3.553 0.059 19.055 0.318 30.343 0.506 1.093 0.018 1.188 0.020 Villa 3.518 0.059 3.565 0.059 26.548 0.442 35.758 0.596 1.070 0.018 1.163 0.019 VIHb 4.218 0.070 4.270 0.071 34.473 0.575 42.345 0.706 1.114 0.019 1.211 0.020 For More Information The other fact sheets in this series and additional information are available on the Office of Transportation and Air Quality's Web site at: Emission factor fact sheets: Modeling and estimating vehicle emissions: Fuel economy: Improving fuel economy and reducing emissions: Finding the "greenest" vehicle: www.epa.gov/otaq/consumer.htm www.epa.gov/otaq/models.htm www.epa.gov/fueleconomy www.fueleconomy.gov/ www.epa.gov/epahome/trans.htm www.fueleconomy.gov/feg/drive.shtml www.epa.gov/greenvehicles Endnotes 1. The MOBILE model includes PM estimates for heavy-duty diesel vehicles only during idle operation because there has been insufficient emission testing of PM for gasoline-fueled vehicles of the type necessary to develop emission rates for these vehicles at idle, since the PM contribution to ambient air quality from gasoline vehicles and the few light duty diesel cars and trucks in the fleet is normally negligible. ------- 2. Figures presented in this fact sheet are averages only. Individual vehicles can differ substantially in the amount of pollution emitted while idling from the values indicated here. Emission rates may differ slightly from original sources due to rounding, 3. All of the emission estimates provided in this document are consistent, in terms of assumptions made and modeling methodology, with those provided in the other fact sheets in this series: "Average Annual Emissions and Fuel Consumption for Gasoline-Fueled Passenger Cars and Light Trucks" (EPA420'F-08-024), "Average In-Use Emissions from Heavy-Duty Trucks" (EPA420'F'08'027), and "Average In-Use Emission Factors for Urban Buses and School Buses" (EPA420-F-08-026). ------- |