University of Colorado at Boulder researchers have found, ironically, that two pollutants -- carbon dioxide and hydrocarbons emitted from agricultural forest trees -- offset each other somewhat in mitigating air quality problems. Carbon dioxide, believed by scientists to be a major factor in greenhouse warming, has been shown to reduce "agriforest" emissions of hydrocarbons that contribute to ground-based ozone pollution, according to CU-Boulder doctoral candidate Todd Rosenstiel of the environmental, population and organismic, or EPO, biology department.