The Devil is always in the details. It is being widely reported on the web that a new University of Tennessee study by Chris Cherry, assistant professor in civil and environmental engineering, and graduate student Shuguang Ji shows that, when electric cars are charged by grid power where the energy mix is 90% coal, they are more polluting than petrol vehicles. But when we take a careful look at the study, several clarifications come to light that tend to discredit the study and marginalize the results.
–>Also see: detailed response to comments on this post and discussion of EV myths: EV in a Frightening Chinese Haze
Marginalizing the Results
There are two qualifications of this study that tend to limit its application. First, it studied 34 Chinese cities. Secondly, it was a study of particulate matter.
China is not typical of the rest of the world. It is hard to imagine pollution so bad that a haze was visible across the lobby of a Northern China hotel where I stayed 8 years ago. The sun was never visible (on a “clear” day) and it was never possible to see across the street. This pollution was primarily particulates from coal-fired power plants mixed with smog. They have expanded their economy rapidly and, because they have vast deposits of coal, this is the primary source of energy they have relied upon for new electrical power plants. The advantage of such plants is that they are relatively cheap to build. The construction is proceeding so rapidly that they have been adding a coal-fired power plant a week. The cost of operating such plants, however, is not only the coal but the externality of pollution associated with it.
A study in such a place does not extend to most places in the world—you cannot generalize those results and apply them to very many places.
Different Kinds of Pollution
There are many kinds of pollution. Automobile Pollution is known for NOx (which eventually changes into smog), carbon dioxide, carbon Monoxide, and various other emissions. The particulate level of gasoline engines is relatively low and one of the reasons we don’t use as many diesel engines is that the particulate level is higher for that fuel. Coal pollution, however, is high in particulates. If the study had, instead of particulates, measured CO2, NOx, or carbon monoxide, the reverse results would likely have been found.
A Matter of Degree
Science is like a knife. It can be used for surgery, murder, or our daily bread. In this case, the study has a narrow subject matter: particulates. Its conclusion is further limited to those places where coal is a very large percentage of the electrical energy mix. The US national electrical energy mix for coal is now around 43%. The other nations of the world that have an energy mix that relies so heavily on coal is Australia and South Africa.
It is also a snapshot in time. The electric car is not the problem—power plants are. As the grid becomes cleaner over time, the EV is best positioned to take advantage of that change. It would be hazardous to rely upon the study for any future course of action without considering the trend of the electrical energy mix. In the US, the electrical energy mix for coal has gone from 55% to the present 43% in the last 8 years. In the EU, 70% of new power capacity in 2011 was from renewables.
An electric car, at least, has the possibility of using a clean source for its energy charge, but an internal combustion engine is always going to be burning something and producing pollution no matter what the fuel.
Under the high pressure and temperature conditions in an engine, nitrogen and oxygen atoms in the air react to form various nitrogen oxides, collectively known as NOx. Nitrogen oxides, like hydrocarbons, are precursors to the formation of ozone. They also contribute to the formation of acid rain. (emphasis added)
When we consider that there are many more petrol vehicles than electric vehicles, the major pollution concern is not a few EVs, but dirty power plants and petrol vehicles.
The study also concludes that “electric cars are more harmful to public health per kilometer traveled in China than conventional vehicles.” The important qualification is “per kilometer traveled” and “in China.” With fewer electric cars, the impact is less. In other locations, the study results will not be valid.
But even within China, the study also at times lumps electric bikes with electric cars and confusingly suggests that “electric vehicles in China outnumber conventional vehicles 2:1,” when the vast majority of these are electric bicycles (and the study is focused on cars). It is unclear if the study, when calculating results, included the pollution from refineries or the time-shaving that an EV can do to reduce pollution (or that they can charge with essentially no added pollution during off-peak hours.)
Apples, Oranges, and a False Premise
The study attempts to build upon the fallacy of what has come to be known as the “long tailpipe argument.” The electric car does not pollute in its operation. At issue is the source of energy for a battery vehicle while charging. We can compare individual cars to the general fleet (energy users, power demand, “apples”) or we can compare individual power plants to all power plants (energy suppliers, power supply, “oranges”) and we can even compare all energy demand to all energy supply. What we can’t do is suggest a particular vehicle is being powered by a particular supply as long as there is an electrical grid between the two (apples and oranges). We have to consider the number of vehicles when there is an energy grid between the two.
We can only draw conclusions based upon the size of the electric fleet and the spectrum of power sources. In the US, for example, we could as easily focus on the clean power sources as the dirty ones. In the US, we presently have enough clean sources of electricity (wind, solar, geothermal, hydroelectric…) to power over 100 million electric cars. This is what is available today. Tomorrow, this number will be even larger as more renewable resources are used for electrical production. China is also building its clean power sources at the same time it is introducing electric cars. Its clean electric power supply will also far exceed the number of electric cars.
So, before we become alarmed by a study that seems to search for its conclusion, it is good to take a careful look at what it is attempting to say, if anything.
Photo Credit: Leo Fung
We share this World; its past, present resources and our combined future. With every aspiration, the very molecules we use for life are passed to others through time and space so that each of us may be considered a Breath on the Wind. This part of the world's consciousness lives in NYC; has worked in law, research, construction, engineering; has traveled, often drawn to Asia; writes on Energy and Electric Vehicle issues and looks forward to all your comments. "If you would persuade, you must appeal to interest rather than intellect." - Benjamin Franklin