Think Motorcycles and Scooters are Great for the Environment? Wrong!
http://ecomodder.com/blog/motorcycles-scooters-great-environment-wrong/The reason why scooters and motorcycles pollute so much more is because there is much less regulation when it comes to these vehicles. Technical and market restrictions have made it difficult to pass legislation cleaning up motorcycle tailpipes for years. For example, because most motorcycles and scooters are smaller and cheaper than cars, adding modern catalytic converters and emissions systems would add a tremendous amount of weight and cost to most 2-wheeled vehicles. This means that, unlike cars’, motorcycle and scooter exhaust is heavily polluted.
and...
Motorcycles Create More Greenhouse Gas Emissions than SUVs
http://carbonpig.com/article/motorcycles-create-more-greenhouse-gas-emissions-suvsFederal regulations help to control motorcycle emissions, but the regulations don't do enough to make them emissions competitive with a hybrid car, which, if it were represented in this chart above, would easily prevail as the most efficient vehicle per PMT. Looking up the exact amount of emissions that are generated from a specific model of motorcycle is quite difficult because manufacturers aren't required to test and register the fuel economy with the Environmental Protection Agency. Auto manufactures, on the other hand, have to test every make and model and report the fuel economy.
And finally...
Motorcycles Pollute More Than SUVs
http://www.wired.com/autopia/2008/06/motorcycles-pol/Turns out the average motorcycle is 10 times more polluting per mile than a passenger car, light truck or SUV. It seems counter-intuitive, because motorcycles are about twice as fuel-efficient as cars and emit a lot less C02.
So what gives?
Susan Carpenter lays it all out in a Los Angeles Times column. She found that, although motorcycles and scooters comprise 3.6 percent of registered vehicles in California and 1 percent of vehicle miles traveled, they account for 10 percent of passenger vehicles’ smog-forming emissions.
Motorcycle engines are twice as efficient as automobile engines, she notes, so they generally emit less carbon dioxide. But they emit large amounts of nitrogen oxides, which along with hydrocarbons and carbon monoxide are measured by state and federal air quality regulators to determine whether vehicles meet emissions rules.
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Here is the google link if you wish to read more, there are dozens of articles on this.
http://www.google.com/search?q=do+motorcycles+more+co2%3F&hl=en&gs_sm=e&gs_upl=109l21980l0l22246l35l31l1l21l21l1l282l1719l1.5.3l9l0&spell=1&sa=X&oq=do+motorcycles+more+co2%3F&aq=f&aqi=&aql=1