Electric cars, heralded as environmentally friendly, may cause more harm to the environment than their gasoline-burning counterparts, a new study found.

The study examined 34 major Chinese cities and found that electric cars caused 19 times more particulate matter pollution, which consists of acids, organic chemicals, metals, and dust, than gasoline cars.

An implicit assumption has been that air quality and health impacts are lower for electric vehicles than for conventional vehicles, Chris Cherry, assistant professor in civil and environmental engineering at the University of Tennessee, Knoxville, and one of the study's co-authors, told Eurekalert. Our findings challenge that by comparing what is emitted by vehicle use to what people are actually exposed to.

Electric vehicles in China outnumber conventional vehicles 2:1 and cause indirect pollution from the way the electricity that powers the cars is made. Eighty-five percent of electricity production in China comes from the burning of fossil fuels, and approximately 90 percent of that production is from coal, according to the study. The burning of coal causes a variety of heavy metals such as lead and mercury to be released into the environment as well as large amounts of carbon dioxide and toxins such as hydrogen cyanide.

The study emphasizes that electric vehicles are attractive if they are powered by a clean energy source, Cherry told Eurekalert.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 findings were published in the journal Environmental Science and Technology,

This study raises the question of whether the increase in electric vehicles in the United States could lead to similar problems. The United States produced 3,884 terawatt hours of electricity in 2010, the latest year numbers are available for, according to the U.S. Energy Information Administration. Of that, approximately 3,223 TWh, 83 percent, was produced using fossil fuels. Despite the country's reliance on fossil fuels, however, Cherry said he does not believe the United States needs to worry about the same kind of pollution.

Even though we still generate a lot of energy from coal in the U.S., we have a lot of pollution control, Cherry said. He added that the United States has anti-pollution laws that China does not, which help moderate emissions here. Our environmental protection laws have set thresholds [for pollution emissions], so what that did was force the power sector to adopt technologies to reduce emissions, such as scrubbers on smokestacks.

The researchers found that pollution from electric vehicles affected more people than conventional vehicles. Using pollution models, the researchers estimated that half of the pollution generated from power plants was breathed in by rural dwellers.

Cherry stressed that not all of China relies on fossil fuels for electricity. All China is not the same, he said. Some parts have about 50 percent of the power generated from clean electric sources, generally in the southwest. The northeast has 100 percent coal power. He added that he foresees China fixing the emission rates throughout the country.

The silver lining of this is China has a lot of improvement that can happen, and when it does, electric vehicles will look a lot better, he said.