First field study finds soot particles absorb significantly less sunlight than predicted by models
Viewed as a potential target in the global effort to reduce climate change, atmospheric black carbon particles absorb significantly less sunlight than scientists predicted, raising new questions about the impact of black carbon on atmospheric warming, an international team of researchers, including climate chemists from Boston College, report today in the latest edition of the journal Science.
Mathematical models and laboratory experiments used to study airborne soot particles led to projections that the absorption-boosting chemicals that coat black carbon could yield an increase in absorption by as much as a factor of two. But field studies in smoggy California cities found black carbon absorption enhancements of just 6 percent, suggesting that climate models may be overestimating warming by black carbon, the researchers report.
The surprising results highlight the early challenges in a nascent sector of climate science and could have implications for regulatory efforts to reduce the production of black carbon, or soot, by curbing the burning of fossil fuels. Still, scientists agree that black carbon in the atmosphere has a significant effect on global and regional climate, with earlier studies ranking the warming effects of black carbon particles second only to carbon dioxide gas.
“The team’s field measurements in California showed the enhancement of absorption was very small – approximately six percent instead of by a factor of two,” said Boston College Professor of Chemistry Paul Davidovits, an authority on airborne particles, known as aerosols. “In one respect, it shows that nature is much more complicated than our initial laboratory experiments and modeling indicated. Now we will try to unravel and understand that complexity.”
The historic role of black carbon soot in climate change has been well documented by scientists, most notably in the study of ice samples taken from deep within glaciers. For the past several years, Davidovits has collaborated with Aerodyne Research Inc., and colleagues from universities and government labs in the U.S., Canada and Finland. Their research has focused on the chemical and optical properties of sub-micron airborne particles of black carbon produced by commercial and industrial activity.