Ingenuity is In the Air

NOAA Generates Innovative Tool to Sample Key Component of Atmosphere

The new ASTER with NOAA researchers Dan Murphy (left) and Todd Sanford (right).

The new ASTER with NOAA researchers Dan Murphy (left) and Todd Sanford (right).

High resolution (Credit: NOAA)

When NOAA scientists needed an extremely precise instrument to measure aerosol in the atmosphere, they couldn’t just order one from a catalogue. They had to design and build it themselves.

Aerosol is made up of tiny particles from both natural and man-made sources, and is known to have an effect on our climate. Generally, atmospheric aerosol cools the atmosphere, partially offsetting warming by greenhouse gases.

However, certain types of aerosol — such as black carbon or soot — can warm the surrounding atmosphere and are of growing interest to climate scientists. A particle’s “radiative effect” on climate depends, in part, on how it scatters (a cooling effect) and absorbs sunlight (a warming effect).

Understanding the behavior of atmospheric aerosol is critical for improving our predictions of how climate change will affect the Earth.

Taking Aim at a Climate Uncertainty

ASTER.

ESRL's ASTER.

High resolution (Credit: NOAA)

Today, scientists use a variety of instruments to measure how aerosol scatters and absorbs light. But each device has its own potential for small errors, and every aerosol sample measured may be slightly different. That means aerosol measurements are often not as accurate as they could be.

To address these problems, researchers and engineers at NOAA’s Earth System Research Laboratory (ESRL) in Boulder, Colo. developed ASTER (Aerosol Scattering To Extinction Ratio) — a test instrument that measures a single aerosol particle’s light scattering and absorption simultaneously.

“In climate models, the uncertainty around aerosol effects is usually very large,” said scientist Todd Sanford, who, with his colleague Daniel Murphy, is leading ASTER’s development. “The idea of this instrument is to help reduce that uncertainty.”

A Successful Trial Run

Construction next to the ESRL in Boulder, Colo.

Construction next to the ESRL in Boulder, Colo.

High resolution (Credit: NOAA)

In a test of air pulled from outside ESRL, where a nearby construction project produces dust and engine exhaust, Sanford found that most of the sampled particles were purely scattering (cooling), but a small fraction were dark and more heat absorbing.

The more traditional “bulk” measurement, which measures the combined effect of all particles in a sample, could have concluded only that the aerosols from the construction site were primarily scattering and, therefore, cooling.
“The bulk measurements are very useful, but important information is lost in the averaging process,” Sanford said. “We would have missed these highly absorbing particles, which are very important to the warming effects of the aerosol.”

Foothills behind the ESRL, where ASTER may be initially field-deployed.

Foothills behind the ESRL, where ASTER may be initially field-deployed.

High resolution (Credit: NOAA)

Field Tests Later This Year

Sanford hopes to test ASTER in the field sometime this year, in the foothills behind the Boulder lab. He also wants to compare the instrument’s measurements with existing aerosol instruments. With luck, ASTER could be used to take measurements from the ground during CalNex, a 2009–2010 mission to study climate change and air quality in California. Ultimately, ASTER could flown on research aircraft missions.

You can learn more about the research at NOAA’s Earth System Research Laboratory. To learn more about planned measurements in 2010 in California, visit the ESRL’s CalNex 2010 Web site. NOAA logo.