University of Tennessee researchers say electric cars in China could be more harmful to health than gasoline-powered vehicles because of the way electricity is generated in the country.

Chris Cherry, an assistant  professor of civil and environmental engineering, and graduate student Shuguang Ji analyzed the emissions and environmental-health impacts of five vehicle technologies in 34 major Chinese cities, focusing on dangerous fine particles.

The researchers evaluated health impacts in China using overall emissions data and emission rates from literature about gasoline and diesel cars, diesel buses, electric bikes and electric cars. They then calculated the proportion of emissions inhaled by the population.

What they found defies conventional logic: Electric cars cause more overall harmful particulate-matter pollution than gasoline cars.

Particulate matter includes acids, organic chemicals, metals and soil or dust particles. It also is generated through the combustion of fossil fuels.

The electric cars' impact was lower than that of diesel cars but equal to that of diesel buses. Electric bikes yielded the lowest environmental-health impact per passenger per kilometer (0.6 miles).

Combustion emissions occur in electric vehicles where electricity is generated, rather than where the vehicle is used. In China, 85% of electricity production is from fossil fuels and about 90% of that is from coal.

The researchers discovered that the power generated in China to operate EVs emit fine particles at a much higher rate than gasoline vehicles.

However, because the EV-related emissions often come from power plants located away from population centers, people breathe in the emissions at a lower rate than from conventional vehicles.

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

“The study emphasizes that electric vehicles are attractive if they are powered by a clean energy source,” Cherry says in a statement.

“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.”

Cherry says the findings also highlight the importance of considering exposures and the proximity of emissions to people when evaluating EVs’ environmental-health impacts.

The results also illuminate the distributional impact of moving pollution out of cities. About half of the EV-generated urban emissions are inhaled by rural populations, which generally have lower incomes.

“An implicit assumption has been that air quality and health impacts are lower for electric vehicles than for conventional vehicles,” Cherry says.

“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.”

The researchers conducted their study in China because of the popularity of electric bikes and electric cars and the country's rapid growth. Electric vehicles, including electric bikes, in China outnumber conventional vehicles 2:1.

They say electric bikes in China involve the single largest adoption of alternative-fuel vehicles in history, with more than 100 million units purchased in the past decade.

This, they say, is more than all other countries combined.