Cars and Air Pollution

According to the EPA, in typical urban areas cars, buses, trucks, and off-highway mobile sources such as construction vehicles and boats produce at least half of the hydrocarbons and nitrogen oxides. Even though nationally these pollutants are created from a great variety of industrial and combustion processes, the personal automobile is the single greatest polluter.

Many people typically associate air pollution with the billowing smokestacks of large industries. Air pollution emissions from each individual car are generally small. America's population of automobiles and drivers are increasing. This combined with the traffic congestion of urban areas results in a very large amount of air pollution. The emissions from the millions of vehicles on our nation's roads each day contribute substantially to our air pollution problems. Driving a private car is probably a typical citizen's most "polluting" daily activity.

The power to move a car comes from burning fuel in an engine. Pollution from cars comes from by-products of this combustion process (exhaust) and from evaporation of the fuel itself.

While ozone is not emitted directly from automobiles, the unstable compound is formed in the atmosphere through a complex set of chemical reactions involving hydrocarbons, oxides of nitrogen, and sunlight. The rate at which the reactions proceed is related to both temperature and intensity of the sunlight. Because of this, problematic ozone levels occur most frequently on hot summer afternoons.

When DEQ issues an Ozone Advisory or Alert, we suggest certain voluntary actions to help reduce ozone formation:

  • Limit automobile use by carpooling, walking or riding the bus.
  • Avoid driving during congested "rush hour" traffic and at lunchtime.
  • Postpone or combine errands.
  • Replace face-to-face meetings with conference calls.
  • If possible, telecommute and participate in flextime or compressed-work-weeks.
  • Keep your car well tuned and avoid jackrabbit starts and excessive idling.
  • Avoid use of oil-based paints and solvents.
  • Refuel motor vehicles and mow lawns during the late afternoon or evening hours only.

The majority of these suggested voluntary actions relate to how you drive your vehicle. To help you better understand the significant amount of positive influence that you can have on Arkansas Air Quality, we have provided some interesting information.

The Commuter Calculator tool will allow you to perform a cost analysis of your weekly driving routines. By entering a few facts about how many miles you drive, the fuel efficiency of your vehicle and the price of fuel, you are provided with daily, monthly and yearly cost totals. By carpooling, even with just one other person, the potential financial savings are quickly calculated for you. If you add more members to the car pool, you can increase your savings even more!

The Green Vehicle Guide will help you choose the cleanest and most fuel-efficient vehicle that meets your needs.  The EPA website will help consumers make more environmentally-informed choices when purchasing a vehicle. The Green Vehicle Guide lists pollution levels for all recent model year passenger vehicles sold in the United States. Consumers can select a vehicle model, determine how clean it is relative to other vehicles, comparison shop for similar vehicles, and choose the cleanest vehicle that meets their needs.

Pounds of Pollution1

Air pollution is a difficult concept to grasp. While we often can't see air pollution, automobiles create many different kinds of emissions. Air pollution is often referred to in terms of pounds. You know that air has weight, but how much of a gas is a pound?

If you use your chemistry and math skills to complete this activity, you will be able to provide a interesting visual display to others and help to raise awareness about air pollution.


  • To calculate the weight of various pollutants
  • To visualize the amount of air pollution emitted by a car each year


  • Many 2-liter soda bottles


  1. Calculate the volume of 1 pound of whatever air pollutant you are interested in by using the following equation: (See Explanation A)
    454 g x 1 mole x 22.4 L = liters of gas
    1 lb "X" g 1 mole pounds
  2. Calculate how many 2-liter bottles are needed for the display. Use the following equation: (See Explanation B)
    volume of 1 lb of the pollutant = total bottles
    2 L
  1. There are 454 grams in a pound. The first step is to find out how many grams of the chosen pollutant are in a mole. This number can be calculated using values from the Periodic Table of Elements. Add the grams per mole for each compound. For example, one atom of oxygen is 16 grams per mole and carbon is 12 grams per mole. This totals 44 grams per mole of carbon dioxide molecule. (CO2 is 2 oxygen atoms plus 1 carbon atom.) For your convenience, we have listed the weights of carbon dioxide, carbon monoxide, and nitrogen dioxide, three pollutants given off by cars. Insert these values for "X" depending on the pollutant:

    CO2 = 44g
    CO = 28g
    NO2 = 46g

    There are 22.4 liters in a mole. Multiply by this number of liters and you have converted the pound of gas into an equivalent number of liters.

  2. For example, if you are dealing with CO2, which you have calculated to be 231 liters per pound, divide 231 by 2. This tells you that you need 115.5 two-liter bottles to represent one pound of CO2.

    Answer:  Number of 2-liter bottles:
    CO2 = 115.5 bottles
    CO = 181.5 bottles
    NO2= 110.5 bottles

Emission Facts: Average Annual Emissions and Fuel Consumption for Passenger Cars and Light Trucks

The figures presented in EPA420-F-00-013, April 2008 are averages only. Individual vehicles may differ in miles traveled and pollution emitted per mile than indicated here. Emission rates and fuel consumption totals may differ slightly from original sources due to rounding.


The emission rates for hydrocarbons (both volatile organic compounds [VOC] and total hydrocarbons [THC]), carbon monoxide (CO), oxides of nitrogen (NOx), and particulate matter (PM10 and PM2.5) shown in the following tables are from the U.S. Environmental Protection Agency (EPA) highway vehicle emission factor model Mobile 6.2. They assume an average, properly maintained vehicle on the road in July 2008 operating on typical gasoline on a warm summer day. Emissions may be higher in very hot (especially HC) or very cold (especially CO) weather.

The calculations for Total Annual Pollution Emitted and Fuel Consumed are based on average annual passenger car miles of 12,000 miles and an average annual light truck mileage of 15,000 miles. Fuel consumption is based on fleetwide average in-use fuel economy of 24.1 miles per gallon (mpg) for passenger cars and 17.3 mpg for light trucks.

Passenger Car
Pollutant / Fuel Emission &
(per mile
Calculation Annual
Emission &
VOC 1.034 g (1.034 g/mi) x (12,500 mi/yr) x (1 lb/454 g) 27.33 lb
THC 1.077 g (1.077 g/mi) x (12,500 mi/yr) x (1 lb/454 g) 28.47 lb
CO 9.400 g (9.400 g/mi) x (12,500 mi/yr) x (1 lb/454 g) 248.46 lb
NOx 0.693 g (0.693 g/mi) x (12,500 mi/yr) x (1 lb/454 g) 18.32 lb
PM10 0.0044 g (0.0044 g/mi) x (12,500 mi/yr) x (1 lb/454 g) 0.12 lb
PM2.5 0.0041 g (0.0041 g/mi) x (12,500 mi/yr) x (1 lb/454 g) 0.11 lb
CO2 368.4 g (368.4 g/mi) x (12,500 mi/yr) x (1 lb/454 g) 9,737.44 lb
Gasoline Consumption 0.04149 gal (12,000 mi/yr) x (24.1 mi/gal) 497.93 gal
Light Truck
Pollutant / Fuel Emission &
(per mile
Calculation Annual
Emission &
VOC 1.224 g (1.224 g/mi) x (15,000 mi/yr) x (1 lb/454 g) 32.35 lb
THC 1.289 g (1.289 g/mi) x (15,000 mi/yr) x (1 lb/454 g) 34.07 lb
CO 11.84 g (11.84 g/mi) x (15,000 mi/yr) x (1 lb/454 g) 312.95 lb
NOx 0.95 g (0.95 g/mi) x (15,000 mi/yr) x (1 lb/454 g) 25.11 lb
PM10 0.0049 g (0.0049 g/mi) x (15,000 mi/yr) x (1 lb/454 g) 0.13 lb
PM2.5 0.0045 g (0.0045 g/mi) x (15,000 mi/yr) x (1 lb/454 g) 0.12 lb
CO2 513.5 g (513.5 g/mi) x (15,000 mi/yr) x (1 lb/454 g) 13,572.69 lb
Gasoline Consumption 0.05780 gal (15,000 mi/yr) x (17.3 mi/gal) 693.64 gal


  • These emission factors and fuel consumption rates are averages for the entire in-use fleet as of July 2008. Newer vehicles generally emit less pollution and use less gasoline, while older vehicles generally emit more pollution and use more gasoline. This is due to several factors, including the increasing stringency of emission standards over time and the deterioration (degradation) in the performance of emission control technology (e.g., catalytic converters) with increasing age and accumulated mileage.
  • Carbon dioxide (CO2), while not regulated as an air pollutant, is the transportation sector’s primary contribution to climate change. Carbon dioxide emissions are essentially proportional to fuel consumption (and inversely proportional to fuel economy) – each 1% increase in fuel consumption results in a corresponding 1% increase in carbon dioxide emissions. About 19.4 lb CO2 is produced for every gallon of gasoline combusted. Passenger cars and light-duty trucks also emit small amounts of other greenhouse gases (GHGs); thus, total GHG emissions from these vehicles are slightly greater than the CO2 emission totals shown in this fact sheet.
  • 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: “Idling Vehicle Emissions” (EPA420-F-08-025), “Average In-Use Emission Factors for Urban Buses and School Buses” (EPA420-F-08-026), and “Average In-Use Emissions from Heavy-Duty Trucks” (EPA420-F-08-027).

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:

Want more information about cars and pollution? Check out these EPA fact sheets.

1 Adapted with permission from the 1995 Wisconsin Dept. of Natural Resources "Where's the Air" Study Guide.