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Atmospheric Sciences & Global Change
Research Highlights

September 2015

Good Is Not Enough:
Improving Measurements of Atmospheric Particles

PNNL finds new approach that extends existing methods to challenging-conditions

DOE's G-1 aircraft ready for take-off
The U.S. Department of Energy’s Gulfstream-1 aircraft collects data that a team of experts led by PNNL used to develop an approach estimating the properties of tiny airborne particles that can affect climate. Photo courtesy of the ARM Climate Research Facility. zoom Enlarge Image.
TCAP aerosol plume off NE US coast
A large aerosol particle plume moves eastward in this "True-color Sea-viewing Wide Field-of-view Sensor (SeaWiFS)" image over the North Atlantic Ocean near Cape Cod. These aerosols are part of the particles suspended in the atmosphere that affect the amount of sunlight reaching the Earth, or scattered in the atmosphere. Image courtesy of the NASA EOS Project Science Office. zoom Enlarge Image

Results: When it comes to understanding how atmospheric particles affect climate, one measurement can't tell the whole story, especially in areas that haven't been studied. A research team led by Pacific Northwest National Laboratory developed an approach that links the scattering coefficient, a measure of how much tiny particles suspended in the atmosphere scatter sunlight, with other particle properties. These properties include particle size, chemical composition, and ability to soak up atmospheric water. By linking these measurements, scientists can better understand the effects of a wide range of particles, including those that scatter sunlight (non-absorbing particles) and those that both scatter and absorb sunlight (absorbing particles).

"We found that one property influenced the others," said Dr. Evgueni Kassianov, PNNL atmospheric scientist and lead author of the article published in Atmosphere. "Using improved airborne measurements of particle scattering and absorbing properties and chemical composition, we can better measure their size distribution as well."

Why It Matters: Aerosols, tiny airborne particles of dust and pollution suspended in the atmosphere, affect the atmosphere and the surface of Earth by scattering and absorbing light. The sun's light scatters when it is reflected off the particles and redistributed. The particles' absorption of sunlight heats up the atmosphere while at the same time reducing the amount of sunlight reaching Earth. The combined effects of scattering and absorption can either cool or warm Earth's surface and the atmosphere itself. Understanding the properties associated with these particles gives scientists an edge in estimating the particles' impact on our climate.

Methods: The PNNL scientists collaborated with colleagues at the University of Nevada and Brookhaven National Laboratory to develop a mathematical framework for calculating the total scattering of both non-absorbing and absorbing particles at ambient conditions based on data collected from aircraft. They then tested the approach using data collected by the U.S. Department of Energy's Gulfstream-1 aircraft during the recent Atmospheric Radiation Measurement (ARM) Climate Research Facility's Two-Column Aerosol Project, led by Dr. Larry K. Berg, a PNNL researcher and co-author of the research.

Measurements included optical, microphysical, and chemical properties of weakly absorbing particles. The team compared the scattering coefficient obtained by their approach with the scattering coefficient measured on board the aircraft and found good agreement between the estimated and measured scattering coefficients for a wide range of observational conditions. The new approach will enable scientists to accurately estimate these particle properties, even in areas previously unstudied.

What's Next? The research team plans to apply their approach to strongly absorbing particles. Given the increasing availability of aerosol composition data collected from aircraft, the team expects that their approach can be successfully applied to improve understanding of a wide range of sophisticated processes and phenomena related to aerosols, including how properties evolve with time and the dynamic interactions between aerosols and clouds. 

Acknowledgments

Sponsors: The U.S. Department of Energy's Office of Science, ARM Climate Research Facility and Atmospheric System Research Program funded this effort.

Research Team: Evgueni Kassianov, Larry K. Berg, Mikhail Pekour, Duli Chand, Connor Flynn, Mikhail Ovchinnikov, Beat Schmid, John Shilling, Jason Tomlinson, and Jerome Fast, PNNL; James Barnard, University of Nevada at Reno; and Arthur Sedlacek, Brookhaven National Laboratory.

Research Area: Climate & Earth Systems Science

User Facility: ARM Climate Research Facility data

Reference: Kassianov E, LK Berg, M Pekour, J Barnard, D Chand, C Flynn, M Ovchinnikov, A Sedlacek, B Schmid, J Schilling, J Tomlinson, and J Fast. 2015. "Airborne Aerosol In Situ Measurements during TCAP: A Closure Study of Total Scattering." Atmosphere 6(8). DOI: 10.3390/atmos6081069

Related Highlights: Double Bonus: Win-Win for Atmospheric Particle Properties; Fast and Rigorous: Finding Surface Reflectivity by Looking Up at Clouds; Lord of the Wings: Elevated Particles a Rising Star.


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