But what is being overlooked in this assessment, scientists say, is the fact that, in the long run, nitrogen oxides break down methane and ozone, and thus help cool the atmosphere. By reducing only nitrogen oxide emissions, and leaving carbon monoxide emissions¿which usually accompany them¿at normal levels, global warming is actually worsened.
Using a tropospheric Chemical Transport Model (CTM), developed at the University of California at Irvine, researchers from UC-Irvine and the Frontier Research System for Global Change in Yokohama, Japan, calculated the short-term regional effects of the emissions. They then combined them with their findings on long-term global trends of greenhouse gases to determine their combined impact on climate change. The findings reinforce the theory that urban pollutants, as indirect greenhouse gases, play an important role in global warming.