Cars and ground-level ozone: how do fuels compare?

Introduction An important question for policy-makers is how the main automotive fuels - diesel, gasoline, LPG (and increasingly, electricity) - compare in terms of ground-level ozone formation. Methods Based on recent, equivalent emissions data, the study compares ozone formation on a per-kilometre basis of the main fuels: gasoline, diesel, liquefied petroleum gas and electricity (the latter in the United Kingdom). Results Considering tailpipe emissions only, gasoline's and LPG's per-kilometre ozone impact is 44-88% of diesel's, while LPG's is slightly lower than gasoline's. If fuel production and tailpipe emissions are added together, the liquid fuels generate 48-80% of electricity's impact, i.e. the electric car's ozone impact is highest. The liquids' ozone-impact rankings are the same as for tailpipe only, from most to least: diesel, gasoline, LPG. Conclusions Changing the fuel/energy type of a passenger car changes its emission inventory, so this could be a useful policy in combating ozone, i.e. governments could encourage some fuels/energies and discourage others. Based on the results shown above, a priority ranking of the main types, from best to worst in the United Kingdom, is: LPG, gasoline, diesel and battery electric. For electric, this ranking will vary in other regions, depending on the emissions of the power-generation grid. For the liquid fuels, the rankings are valid for Europe and North America in general. Impact assessment of ozone is complex, because the chemistry of its formation is complex. This complexity is only partially incorporated in existing impact assessment methods.