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. 2010 Feb 25;118(6):783–789. doi: 10.1289/ehp.0901622

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PNCs. (A) Bus sampling day, 22 January 2008. Black, diesel bus; gray, electric bus; dotted line, urban background. The diesel bus left and arrived about 15 min later than the electric bus. To facilitate geographical comparison, the time of the diesel bus is shifted 15 min earlier. (B) Car sampling day, 18 March 2008. Black, diesel car; gray, gasoline-fueled car; dotted line, urban background. (C) Bicycle sampling day, 10 June 2008. Black, high-traffic route; gray, low-traffic route; dotted line, urban background. Res., residential.