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

European Transport Research Review, Sep 2017

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.

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

Eur. Transp. Res. Rev. Cars and ground-level ozone: how do fuels compare? 0 Atlantic Consulting , Obstgartenstrasse 14, 8136 Gattikon , Switzerland 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. Ground-level ozone; Road transport; Gasoline; Diesel; LPG; Electricity - The pale-blue gas is classified as a bleaching agent. Inhalation of this bleach is harmful to animals and plants. For humans, elevated levels of ambient ozone cause eye and respiratory irritation, indicated by symptoms such as cough, throat dryness, eye and chest discomfort, thoracic pain, and headache [ 1 ]. Lung function is also reduced, i.e. the lungs are less able to: move air in and out, and to put oxygen into and remove carbon dioxide from the blood. Ozone is also suspected to aggravate cardiovascular function, but this has not been proven conclusively. Short-term (acute) effects of ozone exposure are undisputed. High ozone concentrations cause the above afflictions, which lead to increased hospital admissions and sometimes to death. A summary of 20 European epidemiology studies suggests that for every 5 ppbv increase in ambient ozone concentration, there is a 0.22% increase in daily deaths [ 2 ]. Longterm (chronic) effects of ozone exposure are less clear. Some studies suggest that it causes a permanent reduction in lung function, or that it contributes to heart disease and cancer. These claims are inconclusive [ 3 ], but not disproven. As [ 3 ] point out, the inconclusiveness could be due to: insufficient studies; and/or complications in the data. It can be complicated (and sometimes impossible) to isolate the effects of ozone from those of NOx and particles. Precise deaths rates due to ozone are arguable. As officials of the UK Health Protection Agency point out, estimates of premature deaths can range from 100 to 10,000 per year, depending on where the threshold for ozone activity is set. Estimates of hospital admissions also vary by two orders of magnitude, from 230 to 23,000 [ 4 ]. If the high-end death rates are assumed, then ozone has a mortality rate that is in the same league as that of particle matter (PM2.5), 29,000 deaths per year, and NO2, 23,500 deaths per year [ 5 ]. Ozone particularly preys upon the weaker people in society: the very young, the old and the poor. They are more susceptible to it, through lower defences and/or higher exposures [ 6 ]. 1.1.2 A greenhouse gas Ground-level ozone is a significant contributor to global warming. According to Intergovernmental Panel on Climate Change, IPCC [ 7 ], it is the third-largest source after carbon dioxide and methane (not accounting for black carbon), followed by halocarbons and nitrous oxide. Ozone generates about one-fourth the warming of carbon dioxide. Nonetheless, ozone is not regulated under the UN Framework Convention on Climate Change (Kyoto and Paris Protocols). This is probably because it is a secondary pollutant, and these Protocols focus on primary pollutants. Likewise, ozone appears not to have a recognised global warming potential (GWP). Most greenhouse gases are assigned a GWP by the UNFCCC, but ozone is not, and a literature search has generated no GWP estimates for it. Even a 2016 authoritative estimate listed its GWP as ‘NA’.1 This lack of GWP might be due to ozone’s secondary status. It might also be due to ozone’s low persistence at ground level. It lasts hours-to-days, unlike the other main GHGs that last for years. 1 http://cdiac.ornl.gov/pns/current_ghg.html 1.1 (...truncated)


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Eric Johnson. Cars and ground-level ozone: how do fuels compare?, European Transport Research Review, 2017, pp. 47, Volume 9, Issue 4, DOI: 10.1007/s12544-017-0263-7