With all the talk about carbon dioxide, maybe we're losing sight of the environmental problems caused by combustion of most fuels.  For the first time in years, Los Angeles again topped the list of most polluted cities in the United States -- would cars running on ethanol make such metro areas cleaner?  A recent study [1] shows that to the contrary, ethanol-based vehicles actually may pose a larger risk than today's octane-burning ones. The study considered the pollution resulting from smog processes -- the chemical reactions that happen after the emissions have left the car.  When considered in this larger picture, it turns out that ethanol may actually lead to more respiratory illnesses. Furthermore, ethanol is only slightly better in reducing CO2 emissions than gasoline [2]-- and arguably worse if one also considers the environmental damage from farming. But it's clearly politically savvy to tout the benefits of ethanol -- mak'n them farm jobs and fight'n them terrists -- but mostly it's just hot smoke in your face.  

[1] Mark Schwartz. Ethanol vehicles pose significant risk to health, new study finds , Stanford Report, April 18, 2007

 [2] I. Fushman, "Is Ethanol Worth it? " July 2007