The ASU researchers say the effect of brown carbon is complex because it both cools the Earth's surface and warms the atmosphere.
"Because of the large uncertainty we have in the radiative forcing of aerosols, there is a corresponding large uncertainty in the degree of radiative forcing overall," Crozier says. "This introduces a large uncertainty in the degree of warming predicted by climate change models."
A key to understanding the situation is the light-scattering and light-absorbing properties called optical properties of aerosols.
Crozier and Anderson are trying to directly measure the light-absorbing properties of carbonaceous aerosols, which are abundant in the atmosphere.
"If we know the optical properties and distribution of all the aerosols over the entire atmosphere, then we can produce climate change models that provide more accurate prediction," Anderson says.
Most of the techniques used to measure optical properties of aerosols involve shining a laser through columns of air.
"The problem with this approach is that it gives the average properties of all aerosol components, and at only a few wavelengths of light," Anderson says.
He and Crozier have instead used a novel technique based on a specialized type of electron microscope. This technique monochromated electron energy-loss spectroscopy can be used to directly determine the optical properties of individual brown carbon nanoparticles over the entire visible light spectrum as well as over the ultraviolet and infrared areas of the spectrum.
"We have used this approach to determine the complete optical properties of individual brown carbon nanoparticles sampled from above the Yellow Sea during a large international climate change e
|Contact: Joe Kullman|
Arizona State University