How are Spanish researchers measuring roadway air pollution?

About five percent of the vehicles on the road are responsible for about 90 percent of vehicle emissions, according to researchers at Spain's Universidad Carlos III de Madrid (UC3M). By using a modified infrared multispectral image camera equipped with a wheel of lens filters, researchers can watch slow-moving traffic and identify which vehicles are emitting which gases. The spinning wheel of filters allows multiple images to be taken of each vehicle, as each filter detects a different gas. The information could be used by lawmakers to limit the vehicles that emit the most harmful gases.