The 2014 Nissan Leaf has been named the cleanest car in the country by the Automotive Science Group.

The zero-emissions vehicle was selected as the cleanest production vehicle in the United States after being analyzed in nine categories by the research firm, Autoblog.com reported.

In a "wildly complex" process, ASG inspected more than 1,300 vehicles and measured factors such as how much fuel is needed to keep each car running and what natural resources had to be extracted to build it.

Of the 2014 model year, the Nissan Leaf had the "smallest life-cycle environmental footprint," ASG said in a press release. The plug-in, which runs on an 84-mile battery range, is American-assembled and stands as the best-selling all-electric car in the world.

Other cars that took honors in the ASG study are the Mitsubishi Mirage and the Chevrolet Spark. The Mirage, which weighs less than 2,000 pounds and gets 40 miles per gallon, was the cleanest among gas-powered vehicles, while the Chevrolet Spark had the lowest cost of ownership over five years.

The Leaf was also in the top three greenest cars last month when the American Council for an Energy-Efficient Economy (ACEEE) compiled a list.

According to ASG, the study's intricate system offers solid facts for car shoppers to use when looking for a greener vehicle.

"We believe our Index is the market differentiator for today's hyper-competitive automotive marketplace," Colby Self, ASG managing director, said in the press release.

"Based on the principles of ecological economics, we have developed a comparative automotive assessment that recognizes corporate social responsibility efforts that ultimately lead to the best end-products for the market while remaining financially relevant to mainstream consumers."

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