Air pollutants mainly from cars, trucks and industrial activity are contributing significantly more to the formation of urban haze than previously thought, according to a new study. Jose-Luis Jimenez, an assistant professor of chemistry and biochemistry at the University of Colorado at Boulder and a fellow of the Cooperative Institute for Research in Environmental Sciences, and Rainer Volkamer, a Feodor Lynen Fellow at the University of California-San Diego, were the lead authors of the study published last month in Geophysical Research Letters.