http://www.cartalk.com/blogs/jamie-lincoln-kitman/blue-tec-blues
The only clean hydrocarbon fuel available on filling station forecourts
right now is LPG.
LPG produces 33% less CO2 emissions than petrol and 45% less CO2 than
diesel.
LPG vehicles produce upto 82% less Nitrogen Oxide pollutants than petrol
and 99% better than diesel !
63% less Carbon Monoxide.
40% less Hydrocarbons than petrol and 70% less than diesel.
50% less particulates than petrol and 98% less than diesel. These caused
the London warning in 2005.
http://www.lpg-cars.co.uk/lpgbenefits/