With support from the Environmental Protection Agency (EPA), John E. Mak and his team of scientists are taking atmospheric research to new heights — literally. Piloting a specialized plane as part of a six- week research campaign, Mak took air samples for a study that has never been done before: examining emissions from trees from above the canopy to see how they impact aerosol formation.
Organic compounds emitted from trees into the atmosphere as gases react with other compounds to form particles of organic aerosol. The aerosols impact air quality and contribute to global warming, so it is vital that scientists understand the chemistry behind their creation.
Earlier this spring, Mak, Associate Professor, School of Marine and Atmospheric Sciences/Institute for Terrestrial and Planetary Atmospheres, and his colleagues (Allen H. Goldstein, University of California at Berkeley, and Alex Guenther, National Center for Atmospheric Research) were awarded $399,964 by the EPA to research reactive trace gas emissions. Their project — Emission, Fate, and Contribution of Biogenic Volatile Organic Compounds to Organic Aerosol Formation in the Presence of Anthropogenic Pollution: Measurements and Modeling during SOAS — was part of the Southern Oxidant and Aerosol Study (SOAS), a six-week field campaign that took place this past June and July in Alabama. The goal of SOAS: to better understand biosphere-atmosphere interactions and communicate their findings to the public.
More than 15 teams of researchers and filmmakers — including groups from Colorado State University, MIT, UCLA and University of North Carolina — worked side by side in a forested area in Talladega National Forest near Brent, Alabama. In addition to support from the EPA, The National Science Foundation, the National Oceanic and Atmospheric Administration and the Electric Power Research Institute have invested more than $20 million to cover costs associated with SOAS, including the use of two other research aircraft.
The overall goals of Mak’s project are to quantify Volatile Organic Compound (VOC) emissions from trees, or biogenic emissions, and VOC deposition to terrestrial ecosystems and understand the impact of pollution from people, or anthropogenic emissions, on secondary organic aerosol formation.
For the project, Mak enlisted senior Atmospheric Science doctoral student Luping Su to analyze samples from the flight segment and to take readings on the ground for the entire six weeks. Also on the team for the flight portion of the study were Kim Lamont, Lani Ritter, Alicia Mulalley and Fred Wimberley.
Mak’s team was based at a smaller site within the supersite in the forest. “We were in an oak tree-dominated area in an old growth forest where we were studying trace gas emissions from the oaks using specialized equipment to measure and qualify the emissions,” Mak explained. “The Southeast US is a big source of biogenic hydrocarbons, which are very reactive and of a pure natural origin. We wanted to examine the chemistry of the emissions from the forest. We need to understand it to see how the emissions contribute to aerosol formation.”
The team took a two-pronged approach to their research: examining samples from ground level to the top of the tree canopy and then, using the aircraft to take samples during the climb to 3,000 to 4,000 feet above the canopy. “Canopy readings are what has been done historically but we used the specialized aircraft to sample the air above the canopy. These samples how much of the emissions go above the trees, once released from the trees. This is the first time this has been done,” Mak added. By examining both sets of readings — from below the canopy and above — the team hopes to paint a fuller picture of how aerosols are forming and what this may mean to global warming.
For three weeks, Mak flew the Long-EZ aircraft (owned and operated by UltraPure Air, LLC) and using a system he and his team created, the WASP (Whole Air Sample Profiler), obtained a vertical profile of the distribution of the aerosol particles. With the WASP system the team can collect a continuous ‘core’ of air in the vertical (or horizontal) direction, of about 1000 meter’s length. Mak piloted the plane and could operate the sampling system with the touch of a button.
Back on the ground, these samples were then analyzed by Su using the proton transfer reaction time-of-flight mass spectrometers (PTR-TOFMS). This sensitive time-of-flight machine is one of only five in the United States used for atmospheric research and required someone experienced to run it. Su has been using it for three years in Mak’s lab.
In addition to the flight samples, Su took daily samples from a 44-meter high research tower on site, from the ground up through the canopy of the trees. He worked on calculating the flux of emissions from the forest and qualifying the VOCs on top of the tower from early June to mid July.
The team also collected date from when the other planes in SOAS — the NSF/NCAR C-130 and NOAA P3 used in the supersite — were flying over their area.
Now that the team is back at Stony Brook, they will spend the next few months analyzing the more than 400 GB of data they accumulated, excluding shared data from the other teams. All the SOAS research teams will be sharing data on a collective site so they can compare their observations. In Mak’s lab, Su will be analyzing the data using algorithms he specifically modified for studying emissions.
While it’s too early to report any results from the project, Mak said the “data looks promising but as no one has made such comprehensive measurements like these before, we have little to compare them to.”
“We hope to answer the major question of what role these emissions have in creating gases,” he continues. “Understanding atmospheric process is important. We need to understand the process because there will be changes to Earth in the future and how will those changes impact the atmosphere? If global warming means more forest growth, how will the forest emissions impact the atmosphere? What is the impact on air quality in the region and climate through aerosol production?”
By Shelley Catalano
