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Environment

Researchers find that China's pollution related to e-cars may be more harmful than gasoline cars

February 13, 2012

Electric cars have been heralded as environmentally friendly, but new findings from an international research team suggest that electric cars in China have an overall impact on pollution that could be more harmful to health than gasoline vehicles.

University of Minnesota civil engineering assistant professor Julian Marshall and researcher Matthew Bechle are part of an international team studying the issue. The team is led by University of Tennessee, Knoxville assistant professor Chris Cherry and graduate student Shuguang Ji, and includes Ye Wu from Tsinghua University in Beijing. The study was published in the journal Environmental Science and Technology.

The researchers analyzed the emissions and environmental health impacts of five vehicle technologies in 34 major Chinese cities, focusing on dangerous fine particles. What the researchers found defies conventional logic: electric cars cause much more overall harmful particulate matter pollution than gasoline cars.

"An implicit assumption has been that air quality and health impacts are lower for electric vehicles than for conventional vehicles," Cherry said. "Our findings challenge that by comparing what is emitted by vehicle use to what people are actually exposed to. Prior studies have only examined environmental impacts by comparing emission factors or greenhouse gas emissions."

For electric vehicles, combustion emissions occur where electricity is generated rather than where the vehicle is used. In China, 85 percent of electricity production is from fossil fuels, about 90 percent of that is from coal. The authors discovered that the power generated in China to operate electric vehicles emit fine particles at a much higher rate than gasoline vehicles. However, because the emissions related to the electric vehicles often come from power plants located away from population centers, people breathe in the emissions at a lower rate than they do emissions from conventional vehicles.

Still, the rate isn't low enough to level the playing field between the vehicles. In terms of air pollution impacts, the study found that in China electric cars are more harmful to public health per kilometer traveled than conventional vehicles.

“Our findings are specific to China, which has electrical power plants that emit high amounts of particulate matter pollution and a population that has high numbers of people living in rural areas where power plants are located,” Marshall said. “We’re curious to take this research to the next step to see if we find similar results in other countries.”

The researchers estimated health impacts in China using overall emission data and emission rates from literature for five vehicle types—gasoline and diesel cars, diesel buses, e-bikes and e-cars—and then calculated the proportion of emissions inhaled by the population.

E-cars' impact was lower than diesel cars but equal to diesel buses. E-bikes yielded the lowest environmental health impacts per passenger per kilometer.

"Our calculations show that an increase in electric bike usage improves air quality and environmental health by displacing the use of other more polluting modes of transportation," Cherry said. "E-bikes, which are battery-powered, continue to be an environmentally friendly and efficient mode of transportation."

The findings also highlight the importance of considering exposures and the proximity of emissions to people when evaluating environmental health impacts for electric vehicles. They also illuminate the distributional impact of moving pollution out of cities. For electric vehicles, about half of the urban emissions are inhaled by rural populations, who generally have lower incomes.

"The study emphasizes that electric vehicles are attractive if they are powered by a clean energy source," Cherry said. "In China and elsewhere, it is important to focus on deploying electric vehicles in cities with cleaner electricity generation and focusing on improving emissions controls in higher polluting power sectors." The scientists conducted their study in China because of the popularity of e-bikes and e-cars and the country's rapid growth. Electric vehicles in China outnumber conventional vehicles 2:1. E-bikes in China are the single largest adoption of alternative fuel vehicles in history, with over 100 million vehicles purchased in the past decade, more than all other countries combined.

To read the full research paper, visit the Environmental Science and Technology website.

e-car pollution

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