Replacing diesel fuel in heavy-duty (18-wheeler) trucks with liquefied natural gas has been getting more attractive with every drop in natural gas prices, to the point where the time it takes to pay back a $70,000 added investment cost is under two years (as these trucks are driven 125,000 miles per year). Yet, aside from a lack of refueling stations, enthusiasm for a boom in these trucks has been muted by concern over their global warming potential. Most studies suggest that LNG trucks would be cleaner than diesel trucks on CO2, but that this edge might be lost or even reversed once fugitive methane emissions are counted.
Against this backdrop, a new study (T.C. Bond, et al, 2013; Journal of Geophyscial Research) pushes the needle in favor of LNG trucks. It finds that black carbon emissions, which are emitted by the imperfect burning of diesel fuel but not by natural gas, have twice the global warming potential than previously thought. Granted, in a country where one rarely sees black clouds coming from engine exhausts because diesel particulate emissions are well controlled, this effect may not be large. But in developing countries, where this is a usual occurrence, the consequences for global warming could be significant - as could the disadvantage of diesel relative to LNG.