With temperatures rising like gas prices, scooters may seem the perfect mode of transportation.

You get up to 100 miles per gallon, on top of the hipster factor and the feel of the wind in your hair. But there's one imperfection to these sassy little two-wheeled machines: A March 2005 study by the Environmental Protection Agency shows most scooters on the road pollute more than SUVs.

That sounded so counterintuitive that WW decided to test a few scooters, with help from the crew at Esquire Motors in Goose Hollow, which donated its time and emissions-testing equipment.

Then came the hard part.

Telephone calls and emails seeking scooters to test from scooter shops and groups went unanswered; other scooter owners proved willing to talk—until the story's angle was revealed. Finally, however, we persuaded three scooter lovers to volunteer their vehicles.

Patrick Fitzgibbons, co-owner and founder of P-Town Scooters, let us test his vintage scooter, which established just how bad older models are. Although he knew his pride and joy wasn't the cleanest of motorized vehicles, Fitzgibbons was still surprised by the results.

"How bad is it?" he asked.

Pretty bad. His 1968 Piaggio Gran Turismo, with a two-stroke, 150-cc engine, registered 4,900 parts per million of hydrocarbons and 8.6 percent carbon dioxide emissions. That was 29 times the hydrocarbon levels and nearly three times the carbon dioxide rate of another scooter WW tested—a 2006 MotoFino 150T-10D with a four-stroke engine, courtesy of Prestige Motors in Southeast Portland. The MotoFino kicked out 168 ppm of hydrocarbons and 3.1 percent CO2.

Four-strokes tend to burn cleaner than two-stroke engines, which run on a mixture of fuel and oil. One of Fitzgibbons' customers, Shayne Weinstein, offered up for testing his more modern two-stroke, a 2005 Stella also made by Piaggio. Its levels of 1,100 ppm of unburned hydrocarbons and 7.1 percent CO2 fell in between the older two-stroke engine and the four-stroke.

So why do these numbers matter? Unburned hydrocarbons react with nitrogen oxides in the presence of sunlight and elevated temperatures to form ground-level ozone. The pollutants then cause eye irritation, coughing, wheezing and shortness of breath, and can lead to permanent lung damage. And CO2 is among the main culprits blamed by scientists for global warming.

As for the SUV, we borrowed WW publisher Richard Meeker's 2006 Subaru Tribeca. The six-cylinder engine in Meeker's SUV pumped out less than 10 ppm of hydrocarbons and 1 percent CO2. In other words, the two-stroke scooter WW tested produced about 490 times the hydrocarbons and more than eight times the Co2 of the SUV.

Meeker, who has been disappointed in his car's lower-than-predicted gas mileage (16 mpg combined city/highway) says he's surprised the Tribeca's emissions are so low.

So how do we stick with cool, fun and cheap scooters without stinking up the atmosphere?

Four-stroke engines are a lot cleaner for now. But on the horizon are biodiesel scooters as well as electric and solar-powered prototypes.

Until we reach that harmonic convergence of scooters that are both environmentally astute and chic, two-stroke engine owners should keep their rides in tip-top shape—frequent oil changes, regular tune-ups, the whole spiel. The less funk that accumulates in your engine, the less toxins for everyone to breathe, and there's nothing more hip than that.