Researchers from the University of Minnesota (Minneapolis) found in a new study assessing the life cycle air quality impacts on human health of 10 alternatives to conventional gasoline vehicles “that electric vehicles (EVs) powered by electricity from natural gas or wind, water, or solar power are best for improving air quality, whereas vehicles powered by corn ethanol and EVs powered by coal are the worst.” This study entitled “Life cycle air quality impacts of conventional and alternative light-duty transportation in the United States” and published in the renowned scientific journal ‘Proceedings of the National Academy of Sciences’ (PNAS) constitutes an important contribution to the debate over “environmental impacts of conventional versus alternative transportation options.” Importantly, the authors – Christopher W. Tessum, Jason D. Hill, and Julian D. Marshall – emphasizethat their “results reinforce previous findings that air quality-related health damages from transportation are generally comparable to or larger than climate change-related damages.”
Evaluating the air quality-related human health impacts of light-duty transportation in the US by comparing 10 options using alternative fuels – “including the use of liquid biofuels, diesel, and compressed natural gas (CNG) in internal combustion engines; the use of electricity from a range of conventional and renewable sources to power [battery] electric vehicles (EVs); and the use of hybrid EV technology” – the researchers find “that powering vehicles with corn ethanol or with coal-based or ‘grid average’ [i.e. projected 2020 US average electric generation mix] electricity increases monetized environmental health impacts by 80% or more relative to using conventional gasoline. Conversely, EVs powered by low-emitting electricity from natural gas, wind, water, or solar power reduce environmental health impacts by 50% or more.”
All scenarios in the graphic below represent increases in vehicle miles traveled and show concentrations of regulated air pollutants to increase in almost all scenarios.
Scenarios Depicting Changes in Annual-Average Concentrations of Regulated Air Pollutants
Source: “Life cycle air quality impacts of conventional and alternative light-duty transportation in the United States (PNAS) by Christopher W. Tessum, Jason D. Hill, and Julian D. Marshall.
As for scenario H – ‘EV grid average’ – it is crucial to understand that here the underlying projected year is 2020 and that this scenario refers to US average electric generation mix with electric generation infrastructure for this period obviously not fully determined yet. This scenario, however, allows one to draw a conclusion not found in the study; namely, that EVs deployed in Germany and on the German ‘autobahn’ will do much better along all above metrics – resulting in a well-to-wheel emissions advantage over vehicles running on gasoline or diesel – given the underlying and current German energy mix in the wake of the ‘Energiewende’ – a transition away from fossil fuels towards renewable energy sources.
In an age where climate change and mitigation strategies to curb GHG emissions globally top political agendas – especially in the run up to COP21 in Paris 2015 – this research is a timely reminder to policymakers that transportation sector emissions are both substantial and harmful for humans as well as the atmosphere.
Granted, the link between motor vehicle emissions and respiratory illnesses is scientifically limited due to the complexity and difficulties in proper exposure assessments. Nevertheless, in 2012 greenhouse gas emissions from transportation accounted for about 28 per cent of total US greenhouse gas emissions, according to the US EPA. This made it the second largest contributor of US greenhouse gas emissions after the electricity sector with about 32 per cent.
Moreover, the above study combines “estimates of life cycle emissions [i.e., emissions from production (“upstream”) and consumption (“tailpipe”) of the fuel] with an advanced air quality impact assessment. This is significant because the general public often tends to over-simplify and equate zero-emissions with the widespread deployment of electric vehicles. The picture here, however, is much more complex as the new study above illustrates.
Even though it is true that electric vehicles (EVs) – including plug-in hybrid electric vehicles (PHEVs) – typically produce lower emissions than conventional vehicles, only all-electric vehicles have zero tailpipe emissions. In this respect, the US Department of Energy’s Alternative Fuels Data Center explains: “EVs and PHEVs running only on electricity have zero tailpipe emissions, but emissions may be produced by the source of electrical power, such as a power plant. In geographic areas that use relatively low-polluting energy sources for electricity generation, PHEVs and EVs typically have a well-to-wheel emissions advantage over similar conventional vehicles running on gasoline or diesel. In regions that depend heavily on conventional fossil fuels for electricity generation, PEVs may not demonstrate a well-to-wheel emissions benefit.”
Check out below this neat Alternative Fuels Data Center graphic and learn more about annual vehicle emissions in your zip code.
Source: Department of Energy’s Alternative Fuels Data Center; zip code used: Breaking Energy (10012)
In addition, the difference between the least- and most-polluting power generation options for EVs – according to the study – “increases almost sixfold when air pollution damages are considered alongside climate impacts, instead of when climate impacts are considered alone.” As such, the benefits of “pairing EVs with ‘clean’ electricity’” seem apparent. These results, however, do not to suggest that “EVs are the best technology for every transportation need [but rather] an indication of how light-duty transportation fuels could shift to reduce or increase pollution, and [serve as] as an encouragement into the research of less polluting, more sustainable transportation options for the future,” the authors conclude. Read this interesting study in its entirety here.
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