November 29, 2023

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Study finds Amazon rainforest gas affects Earth’s atmosphere

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Study finds Amazon rainforest gas affects Earth’s atmosphere


Study finds Amazon rainforest gas affects Earth’s atmosphere

Gases from plant leaves create a previously unknown atmospheric phenomenon over the Amazon rainforest, according to a new study by scientists at Pacific Northwest National Laboratory (PNNL).

The discovery has major implications for atmospheric science and climate change modeling.


“The tropical Amazon rainforest forms the lungs of the planet, and this study links natural processes in the forest to aerosols, clouds and the Earth’s radiation balance,” said Manish Shrivastava, PNNL geoscientist and principal investigator of the study. I didn’t realize it before.”

The research was recently published in ACS Earth and Space Chemistry A.


Study finds Amazon rainforest gas affects Earth's atmosphere




Fill in missing data gaps

Shrivastava and his colleagues observed large discrepancies between their results and what would be expected based on estimates from existing atmospheric models when studying fine particles in the upper atmosphere.

Further investigation revealed that the key forest-atmosphere interaction that limits the amount of fine particles in the upper atmosphere is missing from current atmospheric models.


Researchers have discovered a previously unrecognized process that involves semivolatile gases produced by plants in the Amazon rainforest and carried into the upper atmosphere by clouds.

These gases are natural carbon-based compounds that condense easily into fine particles in the upper atmosphere.

Shrivastava noted that this method is particularly efficient at producing fine particles at high altitudes and low temperatures.

These fine particles cool the earth by reducing the amount of sunlight reaching the earth.

They also create clouds, which in turn affect precipitation and the water cycle.


“Without a good understanding of the semivolatile sources of organic gases, we simply cannot explain the presence and role of key particulate components at high altitudes,” Shrivastava said.



Key findings in atmospheric processes

Shrivastava’s research project, funded by a U.S. Department of Energy (DOE) Early Career Research Award, involved investigating the formation of aerosol particles called isoprene-epoxydiol secondary organic aerosols (EPOX-SOAs), which Measured by aircraft flying at different altitudes.


IEPOX-SOAs are the building blocks of fine particles found at all heights in the troposphere, the region of the atmosphere that extends from the Earth’s surface to an altitude of about 20 kilometers above the tropics.

However, atmospheric models do not adequately account for these particles and their effect on the clouds above Earth.


Shrivastava noted: “Because the model does not predict the observed IEPOX-SOA loads at altitudes of 10 to 14 km in the Amazon, we got results that I believe are either a model failure or a lack of understanding of the measurements. I can explain what’s going on at the surface, but The conditions at high altitudes cannot be explained.”


Shrivastava and his team searched data collected by the Grumman Gulfstream-159 (G-1) aircraft, a DOE flying laboratory operated by the Atmospheric Radiation Measurement (ARM) Aviation Facility, which was flown to an altitude of 5 kilometers .

The team also compared data collected by a German aircraft known as the High Altitude and Long Range Research Aircraft (HALO), which flew as high as 14 kilometers.

According to Shrivastava, their IEPOX-SOAs should be loaded at least an order of magnitude lower than the measured results, as predicted by the model. Neither he nor his colleagues outside PNNL could explain the discrepancy between the measurements and the model’s predictions.


Before the team’s study, scientists believed that IEPOX-SOAs were formed primarily by a multiphase atmospheric chemical pathway.

However, the atmospheric chemical pathways required to generate IEPOX-SOAs do not occur in the upper troposphere because of extremely low temperatures and dry conditions.

At that altitude, particles and clouds are frozen and starved of liquid water.

As a result, the researchers were unable to explain their formation observed at altitudes of 10 to 14 kilometers with existing models.


To unravel the mystery, the researchers combined specialized high-altitude aircraft measurements with detailed area model simulations, which were then simulated using the supercomputing resources of PNNL’s Laboratory for Environmental Molecular Sciences.

Their research revealed undiscovered parts of atmospheric processes.

A semivolatile gas called 2-methyltetraol is carried by cloud updrafts into the cold upper troposphere.

The gas then condenses into particles that are detected by the aircraft as IEPOX-SOAs.


Shrivastava noted: “This is certainly an important discovery, as it helps us understand how these tiny particles form, and thus provides a new understanding of how natural processes in forests cool the planet and contribute to clouds and precipitation. Accompanied by 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 regulate global warming.”




Opening doors for further atmospheric research

Shrivastava says the team’s findings are only scratching the surface when it comes to understanding this newly discovered atmospheric process and how it affects the formation of fine particles in the atmosphere.

The newly discovered process from plants could explain a wide range of atmospheric particle phenomena over other forested regions around the world, he said.


“In the grand scheme of things, this is just the beginning of what we know and will open up new areas of research for land-atmosphere-aerosol-cloud interactions.

Understanding how forests produce these particles can help us understand deforestation and changing How climate will affect global warming and the water cycle,” Shrivastava said.


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