Why is LPG considered to be environmentally friendly?

Recognised as a low carbon alternative fuel, it emits 33% less CO2 than coal and 12% less than oil. It also emits almost no black carbon, arguably the second biggest contributor to global warming. 

In transport, research by Element Energy and tests undertaken at Millbrook Proving Ground show that converting 10% of medium to large petrol engine cars and vans to dual-fuel LPG would bring savings of 100 kt CO2 and conversion of older Euro 2 or 3 diesel taxis to LPG engines can improve nitrogen oxide (NOx) emissions by more than 90%. This means that LPG is already part of a portfolio of solutions to meet the challenge of urban air pollution.