Friday, August 8, 2008

Better atmospheric modeling of brown carbons -- influential nanoscale atmosphere aerosols

Arizona State University News: Arizona State University researchers have made a breakthrough in understanding the effect on climate change of a key component of urban pollution. The discovery could lead to more accurate forecasting of possible global-warming activity, say Peter Crozier and James Anderson.….As a result of their studies of aerosols in the atmosphere, they assert that some measures used in atmospheric science are oversimplified and overlook important factors that relate to climatic warming and cooling.

The research findings are detailed in the Aug. 8 issue of Science magazine, in the article “Brown Carbon Spheres in East Asian Outflow and Their Optical Properties,” co-authored by Crozier, Anderson and Duncan Alexander, a former postdoctoral fellow at ASU in the area of electron microscopy, and the paper’s lead author. So-called brown carbons – a nanoscale atmospheric aerosol species – are largely being ignored in broad-ranging climate computer models, Crozier and Anderson say.

Studies of the greenhouse effect that contribute directly to climate change have focused on carbon dioxide and other greenhouse gases. But there are other components in the atmosphere that can contribute to warming – or cooling – including carbonaceous and sulfate particles from combustion of fossil fuels and biomass, salts from oceans and dust from deserts. Brown carbons from combustion processes are the least understood of these aerosol components.

…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.

….It’s typical for climate modelers to approximate atmospheric carbon aerosols as either non-absorbing or strongly absorbing. “Our measurements show this approximation is too simple,” Crozier says. “We show that many of the carbons in our sample have optical properties that are different from those usually assumed in climate models.”....

Misleading photo alert! The aerosols in this article do not come from a can. Photo by PiccoloNamek, Wikimedia Commons, under the terms of the GNU Free Documentation License, Version 1.2

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