Amazon Rainforest Gases Affect Earth’s Atmosphere

The findings could fill a gap for climate change, atmospheric research outside the tropics.

According to a new study by scientists at the Pacific Northwest National Laboratory (PNNL), gasses of plant origin are producing a previously unknown atmospheric phenomenon over the Amazon rainforest. This discovery has significant implications for atmospheric science and climate change modeling.

“The Amazon rainforest is the lungs of the Earth, and this study links natural processes in the forest to aerosols, clouds and Earth’s radiation balance in a way that has never been known before,” said Manish Shrivastava, PNNL Earth scientist and primary investigator for the study.

This research was recently published in the journal Earth and Space Chemistry ACS.

Amazon Rainforest PNNL Chart

PNNL Earth scientist Manish Shrivastava and his team identified atmospheric processes that create a type of fine particle above the Amazon rainforest. Through this process, semi-volatile gases, which are naturally occurring carbon-based chemical compounds that can easily condense to form fine particles in the upper atmosphere, are emitted throughout the Amazon rainforest by chemical processes within factories and previously unrecognized surfaces. Credit: Illustration by Nathan Johnson | Pacific Northwest National Laboratory

Fill in the missing data gap

Shrivastava and his colleagues were studying fine particles in the upper atmosphere when they observed a significant difference between their results and what would be expected based on estimates from existing atmospheric models. Further investigation revealed that key forest-atmosphere interactions were missing from current atmospheric models governing the number of fine particles in the upper atmosphere.

The researchers discovered a previously unknown process involving a semi-volatile gas produced by plants in the Amazon rainforest and carried into the upper atmosphere by clouds. These gases are naturally occurring carbon-based chemical compounds that readily condense in the high atmosphere to create fine particles. Shrivastava stated that this method is very efficient in producing fine particles at high altitudes and low temperatures. These fine particles cool the earth by decreasing the amount of sunlight reaching it. They also produce clouds, which affect rainfall and the water cycle.

“Without a full understanding of the semi-volatile sources of organic gases, we cannot explain the presence and role of key particle components at high altitudes,” said Shrivastava.

Important discoveries in atmospheric processes

The Shrivastava research project, funded through the Department of Energy’s (DOE) Early Career Research Award, involves investigating the formation of aerosol particles known as isoprene epoxydiol secondary organic aerosols (IEPOX-SOA), as measured by airplanes at different altitudes.

IEPOX-SOA is an important building block for fine particles found at all altitudes of the troposphere—the region of the atmosphere that extends from the Earth’s surface to about 20 kilometers in elevation above the tropics. However, atmospheric models do not adequately explain these particles and their effect on clouds high above Earth.

“Because the model would not predict the observed IEPOX-SOA loading at altitudes of 10 to 14 kilometers in the Amazon, we got what I believe to be a model failure or a lack of understanding of the measurements,” said Shrivastava. “I can explain it on the surface but can’t explain it at higher altitudes.”

PNNL Aircraft Flying Laboratory

Earth scientists used data collected by flying laboratory planes in the discovery of atmospheric processes that create a type of fine particle over the Amazon rainforest. Credit: Photo by Jason Tomlinson | US Department of Energy Atmospheric Radiation Measurement [ARM] user facilities

Shrivastava and his team explored data collected by the Grumman Gulfstream-159 (G-1), a DOE flying laboratory operated by the Atmospheric Radiation Measurement (ARM) Aerial Facility, which was flown to an altitude of 5 kilometers. The team also compared data collected by a German plane known as the High Altitude and Long Range Research Aircraft, or HALO, which was flown at an altitude of up to 14 kilometers. Based on the modeled projections, their IEPOX-SOA loading should be at least an order of magnitude lower than measured, Shrivastava said. Neither he, nor his colleagues outside of PNNL, were able to explain the difference in measurements and what the model projected.

Prior to the team’s research, it was believed that IEPOX-SOA was formed mainly by a multiphase atmospheric chemical pathway involving the reaction of isoprene in the gas phase and liquid water-containing particles. However, the atmospheric chemical pathways required to make IEPOX-SOA do not occur in the upper troposphere because of the extremely cold temperatures and dry conditions. At that altitude, particles and clouds freeze and water shortages. Therefore, the researchers were unable to explain their observed formation at an altitude of 10 to 14 kilometers using the available models.

To unravel the mystery, the researchers combined high-altitude aircraft-specific measurements and detailed regional model simulations performed using supercomputer resources at the Environmental Molecular Sciences Laboratory at PNNL. Their studies reveal yet-to-be-discovered components of atmospheric processes. A semi-volatile gas known as 2-methyltetrol is transported by cloud streams upward into the cold upper troposphere. The gas then condenses to form particles which are detected as IEPOX-SOA by the aircraft.

“This is certainly an important discovery because it helps our understanding of how these fine particles form, and therefore shines new light on how natural processes in forests cool the planet and contribute to clouds and precipitation,” said Shrivastava. “Along with global climate change and rapid deforestation in many parts of the Amazon, humans are disrupting key natural processes that create fine particles in the atmosphere and modulate global warming.”

Opening the door for further atmospheric research

The team’s findings are only scratching the surface, Shrivastava said, in studying this newly discovered atmospheric process and how it affects the formation of fine particles in the atmosphere. He said the newly identified processes from plants could explain a variety of atmospheric particle phenomena in other forest locations around the world.

“In the grand scheme of things, this is just the beginning of what we know and will open up new frontiers of research in land-atmosphere-aerosol-cloud interactions,” he said. “Understanding how forests produce these particles can help us understand how deforestation and climate change will affect global warming and the water cycle.”

Reference: “Strict Incorporation of Biochemistry and Surface and Inner Plant Convection Regulates Major Fine Particulate Components in the Amazon Rainforest” by Manish Shrivastava, Quazi Z. Rasool, Bin Zhao, Mega Octaviani, Rahul A. Zaveri, Alla Zelenyuk, Brian Gaudet, Ying Liu , John E. Shilling, Johannes Schneider, Christiane Schulz, Martin Zöger, Scot T. Martin, Jianhuai Ye, Alex Guenther, Rodrigo F. Souza, Manfred Wendisch and Ulrich Pöschl, 12 January 2022, Earth and Space Chemistry ACS.
DOI: 10.1021/acsearthspacechem.1c00356

This research was supported by the DOE Early Career award from Shrivastava and the DOE Atmospheric Systems Research, both from the Office of Science Biology and Environmental Research programs. Support for data collection onboard the G-1 aircraft is provided by ARM, the DOE Office of Science user facility. Computational resources for simulations are provided by EMSL, also a user facility of the DOE Office of Science.

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