It's a line the American public has been hearing for a while—switch to an electric car and save the environment. But in China, where there are more than 100 million electrically-powered scooters and cars, alternatively-powered vehicles may be worse for the environment than gasoline-powered vehicles, according to a report released Monday by a team from the University of Tennessee.

The problem in China comes from the way most electricity is generated—more than 75 percent of power in China is generated by coal. So, rather than look at vehicle-emissions alone, where electric cars easily beat gas- and diesel-powered cars, the researchers studied the environmental impact of the whole power chain.

"An implicit assumption has been that air quality and health impacts are lower for electric vehicles than for conventional vehicles," Chris Cherry, one of the University of Tennessee researchers, explains. "Our findings challenge that by comparing what is emitted by vehicle use to what people are actually exposed to."

Essentially, the human health risk with electric vehicles is moved from the exhaust pipe to the areas surrounding coal power plants.

"Electric vehicles are much cleaner when you consider carbon emissions," Cherry says. "But coal power plants emit a number of different pollutions that have very clear health impacts."

Those emissions include fine particles—metals, acids, allergens, and dust that the Environmental Protection Agency says "have shown a significant association … with premature death from heart or lung disease."

About 10 years ago, China set out to revolutionize its streets with electric cars, something that Cherry calls "perhaps the single largest adoption of an alternative fuel in the history of mobility." But because China has a large population that lives near these coal power plants, the emissions from the plants affect nearby humans almost four times as much as gas-operated cars. America has been slower on the uptake. Last year, the Department of Energy estimated that America will have about 1 million electric cars on the road by 2015.

The good news is that America relies less heavily on fossil fuels that emit fine particles, American coal plants are cleaner than Chinese ones, and America has relatively few people who live near power plants.

"The U.S. power sector is much cleaner than China's, even the coal plants are cleaner," Cherry says. "The EPA has enacted some pretty advanced pollution control measures."

Coal accounts for only about half of American electric power, while cleaner natural gas and nuclear energy accounts for about 20 percent each. Because America depends less on coal for its electricity, electric cars a more appealing option here, says Justin Kitsch, vice president of communications at The Electrification Coalition, which advocates a switch to electric vehicles.

"The advantage of the U.S. power sector is the diversity of our energy resources, many of which are domestically produced," he says.

But Cherry says his study clearly shows that electric vehicles aren't the zero-emission savior many expect them to be.

"I think electric vehicles have a lot of promise, but I'm not an evangelist," he says. "There are these electric cars out there touting themselves as being emission free, but you and I both know that's not true."

Kitsch's group says that America should switch to electric cars primarily for the energy independence aspect, not necessarily for any environmental gains.

"If we can break oil's stranglehold on the transportation sector, it'll help reduce the strains on America's national security apparatus," he says. America, he says, has been hamstrung by being forced to buy oil that is produced in "volatile regions" as America relies on its military to protect oil supply lines.

"Our dependence on oil has really limited our foreign policy options," he says.