Tiny particles known as black carbon can pack a heavy punch when it comes to climate change. Gasoline-burning engines, once thought to be minor players in black carbon production, could put out twice as much as was previously measured, according to new field methods (Environ. Sci. Technol., DOI: 10.1021/es2033845). John Liggio and colleagues from Environment Canada and the National Research Council Canada developed a method with a pulsed laser beam that heats black carbon particles to thousands of degrees Celsius. A photometer measures the incandescence of the particles to estimate their mass in real time. Along Toronto highways, the researchers followed 30 heavy-duty, diesel-burning vehicles and collected samples of their exhaust. They found that the trucks belched levels of black carbon similar to those documented by prior studies. Stationary monitors measured particles downwind of the same highways. The scientists ruled out black carbon sources other than gasoline-burning vehicles and proposed that, to explain their high total measurements, the gasoline-burners would have to emit about 75 mg of black carbon per kilogram of fuel, or twice the amount that other scientists have reported.