Los Angeles Times
Two years ago researchers outfitted an electric Toyota RAV4 with a set of test instruments and drove back and forth near four Los Angeles County freeways between 4:30 a.m. and 6:30 a.m., sampling the air.
http://www.latimes.com/news/science/sciencenow/la-sci-sn-freeway-air-pollution-20130417,0,536917.story
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