The tropics are a hugely important region for the earth's atmosphere, especially through the exchanges of heat, moisture, and chemistry that take place across the tropics' vast oceans and lush vegetation. Huge stretches of savanna in Africa are burned each fall and winter for agricultural and other purposes. The fires produce large amounts of hydrocarbons and oxides of nitrogen, which interact with sunlight to produce ozone and other smoglike products--often levels approaching those of a high-pollution day in a major city. The plumes of ozone stretch, at times, as far as South America. In 1996, scientists from the National Center for Atmospheric Research and colleagues took part in the Experiment for Regional Sources and Sinks of Oxidants, which documented biosphere-atmosphere interactions taking place in and near the African tropics.
