sources.

"Advocates for Highway and Auto Safety." Advocates for Highway and Auto Safety | Advocates for Highway and Auto Safety. Web. 09 Nov. 2009. .

“most ozone pollution is caused by motor vehicles, which account for 72% of nitrogen oxides and 52% of reactive hydrocarbons (principal components of smog).”

"Newsvine - Burning 1 Gallon of Gasoline Produces 20 Pounds of CO2." Jg2090.newsvine.com - blinkin. Web. 09 Nov. 2009. .

“For every gallon of gasoline you burn in your car, you remove 21 pounds of breathable Oxygen from the atmosphere, as well as adding 20 pounds of CO2, or Carbon Dioxide to the atmosphere.”

"40 Benefits of Bike Commuting & Recreational Bicycling." International Bicycle Fund: Promoting bicycle transport and economic development and cultural understanding worldwide. Web. 09 Nov. 2009. .

“A four mile bicycle trip keeps about 15 pounds of pollutants out of the air we breathe.”

"Automobiles: Pollution and Energy Use." Bicycle Universe: The kitchen sink of bicycles & transportation. Web. 09 Nov. 2009. .

“Pollution by cars causes lung cancer, respiratory problems, urban smog, and acid rain”
“Most ozone pollution is caused by motor vehicles, which account for 72% of nitrogen oxides and 52% of reactive hydrocarbons”