The light-duty car category excludes some pickup trucks that are marketed to consumers, like the Ford F250 and F350 models.

FORBES: America's Dirtiest Vehicles 2013

Last year, he bought a used 2005 F350 Super Duty turbo diesel pickup to use for his landscape business in Fort Myers, Florida.

CNN: FBI breaks up $25 million 'car cloning' ring

That F350, running on 5% soy-based biodiesel (any more would void the vehicle's warranty), burns 840 gallons of fossil fuel a year doing 15, 000 miles, not including the petroleum used up to make the soy diesel.

FORBES