This is not a list of specific autos that are heavy polluters; rather, the amount of auto pollution depends on a number of factors! Consider this from Treehugger.com:

“A new study by researchers at the University of Toronto found that 25% of cars and trucks are causing about 90% of pollution from vehicles. The scientists made on-the-spot measurements of 100,000 vehicles as they drove past air-sampling probes (including a for the first time a proton transfer reaction time-of-flight mass spectrometer; it provided the time resolution required for the plume capture technique used in the study) on College Street, one of Toronto’s many major roadways. The bottom 25% of the vehicles studied emitted:

• 95% of black carbon (or “soot”)
• 93% of carbon monoxide
• 76% of volatile organic compounds such as benzene, toluene, ethylbenzene and xylenes, some of which are known-carcinogens

“The most surprising thing we found was how broad the range of emissions was,” says Evans. “As we looked at the exhaust coming out of individual vehicles, we saw so many variations. How you drive, hard acceleration, age of the vehicle, how the car is maintained – these are things we can influence that can all have an effect on pollution.”

This means that just by targeting these dirty old clunkers, badly tuned rust-buckets, and street racers, we could make a significant impact on air quality, especially in urban areas where the density of vehicles gets high enough for pollutant concentrations to reach dangerous levels.

Things like Cash for Clunkers, mandatory emission tests (that are frequent and stringent), better policing, and maybe some real-time dashboard feedback to help teach people not to accelerate too fast for no reason could help.”