Something in the air

UI researcher finds black carbon implicated in global warming

Increasing the ratio of black carbon to sulfate in the atmosphere increases climate warming, suggests a study conducted by a University of Iowa professor and his colleagues and published in the journal Nature Geoscience.

Black carbons—arising from such sources as diesel engine exhaust and cooking fires —are widely considered a factor in global warming and are an important component of air pollution around the world, according to Greg Carmichael, Karl Kammermeyer Professor of Chemical and Biochemical Engineering in the UI College of Engineering and co-director of the UI Center for Global and Regional Environmental Research. Sulfates occur in the atmosphere largely as a result of various industrial processes.

In order to conduct the National Science Foundation-funded study, Carmichael and his research colleagues made ground-level studies of air samples at Cheju Island, South Korea, and then sampled the air at altitudes between 100 and 15,000 feet above the ground using unmanned aircrafts (UAVs).

They found that the amount of solar radiation absorbed increased as the black carbon-to-sulphate ratio rose. Also, black carbon plumes derived from fossil fuels were 100 percent more efficient at warming than were plumes arising from biomass burning.

"These results had been indicated by theory but not verified by observations before this work," Carmichael says. "There is currently great interest in developing strategies to reduce black carbon as it offers the opportunity to reduce air pollution and global warming at the same time."

The authors suggest that climate mitigation policies should aim to reduce the ratio of black carbon to sulphate in emissions, as well as the total amount of black carbon released.

Carmichael is chair of the scientific advisory group for the World Meteorological Organization's GURME (Global atmospheric watch Urban Research Meteorology and Environment) project and chair of the scientific advisory group for the Shanghai Expo pilot project on air quality forecasting. He has worked with Shanghai authorities for three years to help develop an early warning system for air quality problems and heat waves.