According to a new study by scientists at the Pacific Northwest National Laboratory (PNNL), plant emissions produced a previously unknown phenomenon in the Amazon rain forest. Discovery has important implications for climate science and climate change modeling.
“The Amazon rain forest forms Earth’s lungs, and this study links forest ecosystems with aerosols, clouds, and the Earth’s luminous luminosity in ways that have never been seen before,” said Mansh Shrivastava, a PNNL Earth scientist and principal research investigator.
Filling in the missing data gap
Shrivastava and colleagues studied the fine particles in the atmosphere when they observed a significant difference between their results and what could be expected based on the estimates of existing aerial models. Further research revealed that the vital interactions between the forest and the atmosphere were not present in current space models that regulate the number of fine particles in the upper atmosphere.
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Researchers are discovering an unknown process that involves the inconsistent gases produced by plants in the Amazon rain forest and that are carried by clouds to outer space. These gases are compounds that are made from carbon-based chemicals that easily decompose in the atmosphere to form fine particles. Shrivastava says that this method is very effective in producing fine particles at high temperatures and at low temperatures. These fine particles are enriching the earth by reducing the amount of sunlight that reaches it. They also produce clouds, influencing rainfall and the water cycle.
“Without a full understanding of the dynamic source of living gases, we cannot simply explain the existence and role of vital particles at high altitudes,” Shrivastava said.
Important discoveries in space processes
The Shrivastava research project, funded by the Department of Energy (DOE) Early Career Research Award, is involved in investigating the formation of aerosol particles known as isoprene epoxydiol secondary organic aerosols (IEPOX-SOAs), which are measured by flying at different altitudes.
IEPOX-SOAs are the key building blocks of the fine-grained particles found in all of the troposphere — a spacecraft that stretches from about 20 miles [20 km] above the tropical regions. However, space models did not adequately respond to these particles and their impact on clouds high above the Earth.
“Since the models would not predict the loading of the IEPOX-SOA loads seen at 10-to-14-kilometer altitudes in the Amazon, we were getting what I believed to be model failures or misunderstandings,” Shrivastava said. “I could describe it at the top but I couldn’t explain it at high altitudes.”
Shrivastava and his team reviewed data collected by Grumman Gulfstream-159 (G-1), a DOE flying laboratory using the Atmospheric Radiation Measurement (ARM) Aerial Facility, which flew up to 5 km in height. The team also compared data collected by a German aircraft known as the High Altitude and Long Range Research Aircraft, or HALO, which flies at an altitude of up to 14 miles. Based on the modeling assumptions, their IEPOX-SOA uploads should be at least a minimum order size than measured, Shrivastava said. No one, or her colleagues outside the PNNL, can explain the differences in estimates and what the models produced.
Prior to the group study, it was believed that IEPOX-SOAs were composed primarily of multiphase atmospheric chemistry pathways that combined the reaction of isoprene into a gas phase with particles containing liquid water. However, the chemical mechanisms needed to create IEPOX-SOAs do not occur in the upper troposphere due to extremely cold temperatures and dry conditions. At that altitude, particles and clouds form ice and there is no liquid. Researchers were therefore unable to define their apparent shape at 10 to 14 kilometers in height using available models.
To solve the mystery, the researchers combined high-level aircraft measurements and detailed regional model simulations performed using supercomputing resources at the PNNL Environmental Scientific Laboratory. Their research revealed an unexplored part of space systems. The semi-volatile gas known as 2-methyltetrol is transported by cloud development in the cold upper troposphere. The gas then thickens to form particles found in the aircraft such as IEPOX-SOAs.
“This is certainly an important discovery because it helps us to understand how these beautiful particles are formed, and as a result sheds new light on how natural processes in the forest cool the planet and contribute to clouds and rain,” says Shrivastava. “Along with global climate change and rapid deforestation in many parts of the Amazon, humans are disrupting vital ecosystems that produce beautiful particles in the atmosphere and measure global warming.”
Opening the doors to further space research
The group’s discovery is only scratches on the surface, says Shrivastava, as he learns about this newly discovered air process and how it affects the formation of fine particles in the atmosphere. He said the newly identified process from plants could explain a wider range of space particles than other forested areas around the world.
“In a larger program, this is just the beginning of what we know and will open new barriers to research on earth-space-aerosol-cloud interactions,” he said. “Understanding the forest’s production of these particles can help us understand how deforestation and climate change will affect global warming and the water cycle.”
Source Journal Reference: 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, Tight Coupling of Surface and In-Plant Biochemistry and Convection Governs Key Fine Particulate Components over the Amazon Rainforest” January 2022, ACS Earth and Space Chemistry. DOI: 10.1021/acsearthspacechem.1c00356
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