Looking to minimize your impact on the environment? Don’t buy a car — and especially don’t buy anything made by DaimlerChrysler. The U.S.-based automaker ranked dead last on a survey, released yesterday by the Union of Concerned Scientists, of pollution levels in vehicle fleets. The survey looked at the environmental implications of the six largest car manufacturers in the U.S. market, which together sell nine out of every 10 vehicles purchased here. Those vehicles account for vast percentages of smog-forming pollution and carbon dioxide emissions in the U.S. From best to worst, the companies were Honda, Toyota, Nissan, Ford, General Motors, and DaimlerChrysler. Toyota was the only company to cut its fleet’s average CO2 emissions between model years 2000 and 2001. The only company to move up in the survey was Ford, which went from being second-to-last in the previous survey to fourth in the current one. UCS credited that change to the environmentally friendly leadership of William Clay Ford, Jr.