PNNL

Catching Cape Cod Aerosols Scientists led by PNNL are gaining insight into aerosol properties along the east coast of the U.S., showing that the tiny particles are present in the atmosphere even on cloud-free days near Cape Cod. Enlarge Image.

Results: The 40 miles of pristine beaches, ponds, and uplands of the Cape Cod National Seashore attract thousands of visitors a year. Few realize that aerosols—tiny airborne particles—lurk just overhead in the misty clouds for which Cape Cod is famous. Now a group of scientists led by Pacific Northwest National Laboratory has discovered elevated levels of aerosols even on cloud-free days. And these aerosols have a large impact on the amount of sunlight reaching the surface.

"Models that are key to understanding climate on a regional and global level struggle to correctly calculate the effects of aerosols along the east coast of America, Asia, and Africa," said Dr. Larry Berg, PNNL atmospheric scientist who led the team. "Our Two-Column Aerosol Project was designed to provide detailed measurements that can be used to evaluate and fine-tune these models."

The year-long study included measurements to examine the chemical composition of the particles, the way they reflect or scatter light, and their ability to act as seeds for cloud drops.

Why It Matters: Anyone who has had their sunny day interrupted by haze has been affected by aerosols. But blocking sunlight is only one of their many traits, and the particles can be surprising complex. They range in size from almost invisible to extremely tiny. They can come from sea spray, dust, and car exhaust, among other sources. They can join up in the air, change their chemical composition, and mix with other particles. All of these changes can affect how they interact with the atmosphere.

"Many climate processes such as heating and cloud formation depend on these continuously changing particles," said Berg. "Modeling has faced the challenge of their complexity by simplifying calculations, but that leads to a broader range of modeling results. The broader the range, the more difficult it is to predict climate."

The data gathered during the Two-Column Aerosol Project will go a long ways toward narrowing that range of possible answers.

Methods: The scientific team from national laboratories and universities sampled a column of air in two locations, one fixed over the Cape Cod National Seashore and the other over the Atlantic Ocean more than a hundred miles from the coast. Two aircraft (including the G-1) equipped with scientific instruments flew through the columns on simple, repeatable flight patterns, with close coordination, so data could be effectively compared over time and space. Additional instruments, deployed at the Highlands Center at the Cape Cod National Seashore, took measurements at the base of the column on Cape Cod.

Scientists also made use of new instruments, which were deployed for the first time during the project:

miniSPLAT, a single particle mass spectrometer developed at PNNL, which can measure the size and chemical composition of individual aerosol particles from inside the plane NASA's Spectrometer for Sky-scanning Sun-Tracking Atmospheric Research (4STAR) mounted on the roof of an aircraft to measure small changes in the amount of sunlight associated with particles in the atmosphere NASA's second-generation High Spectral Resolution Lidar (HSRL-2) to characterize clouds and measure aerosol distribution and movement from a high-altitude aircraft.

The new instruments and data obtained from the in-air sampling gave scientists an unprecedented look at aerosol chemical and other properties off the east coast of the United States.

What's Next? Scientists are currently analyzing the differences among summertime and wintertime conditions. This comparison, as well as all the data collected during the project, will be used to refine regional and global climate models and remove at least some of the uncertainties associated with the complex aerosols. Improving climate models makes spending the summer on Cape Cod all the more worthwhile.

Acknowledgments

Sponsors: The research was supported by the U.S. Department of Energy's Office of Science, Office of Biological and Environmental Research for the Atmospheric System Research program. The Cape Cod National Seashore allowed deployment of ground-based instruments.

Research Team: Carl Berkowitz, Larry Berg, Jerome Fast, Duli Chand, Jennifer Comstock, Connor Flynn, John Hubbe, Evgueni Kassianov, Celine Kluzek, Fan Mei, Mikhail Pekour, Beat Schmid, John Shilling, Jason Tomlinson, Jacqueline Wilson and Alla Zelenyuk-Imre, PNNL; James Barnard, University of Nevada at Reno; Sharon Burton, Richard Ferrare, Johnathan Hair, Chris Hostetler, and Ray Rogers, NASA Langley Research Center; Brian Cairns, NASA Goddard Institute for Space Studies; Stephen Dunagan, Roy Johnson, Jens Redemann, Philip Russell, Michal Segal-Rosenheimer, and Yohei Shinozuka, NASA Ames Research Center; Anne Jefferson and Joseph Michalsky, NOAA Earth Research Systems Laboratory; Kathleen Lantz, Ivan Ortega, and Rainer Volkamer, University of Colorado; Pavlos Kollias and Katia Lamer, McGill University; Arthur Sedlacek III and Stephen R. Springston, Brookhaven National Laboratory; Mark Miller, Rutgers; and Megan Tyrrell, National Park Service

User Facility: ARM Climate Research Facility Mobile Facility and ARM Aerial Facility; EMSL

Reference: Berg L, J Fast, J Barnard, S Burton, B Cairns, D Chand, J Comstock, S Dunagan, R Ferrare, C Flynn, J Hair, C Hostetler, J Hubbe, A Jefferson, R Johnson, E Kassianov, C Kluzek, P Kollias, K Lamer, K Lantz, F Mei, M Miller, J Michalsky, I Ortega, M Pekour, R Rogers, P Russell, J Redemann, A Sedlacek, M Segal-Rosenheimer, B Schmid, J Shilling, Y Shinozuka, S Springston, J Tomlinson, M Tyrell, J Wilson, R Volkamer, A Zelenyuk, and C Berkowitz. 2015. "The Two-Column Aerosol Project: Phase I overview and impact of elevated aerosol layers on aerosol optical depth." Journal of Geophysical Research 121(1): 336-361. DOI 10.1002/2015JD023848

March 5, 2016