Discoveries can fill the gap for climate change, atmospheric research beyond the tropics.
According to a new study by scientists at the Pacific Northwest National Laboratory (PNNL), the gases derived from plant leaves generate a previously unknown atmospheric phenomenon over the Amazon rainforest. The discovery has significant implications for atmospheric science and climate change modeling.
“The Amazon rainforest is the lungs of the Earth, and this study connects natural forest processes to aerosols, clouds and the Earth’s radiative balance in ways not previously recognized,” said Manish Shrivastava, a PNNL Earth scientist and mayor. the investigator of the study.
The research was recently published in the journal ACS Earth and Space Chemistry.
Missing data gap
Shrivastava and colleagues were looking for fine particles in the upper atmosphere when they noticed a significant difference between their results and what would have been expected based on estimates from existing atmospheric models. Subsequent investigations have shown that key forest-atmosphere interactions are missing from current atmospheric patterns that govern the number of fine particles in the upper atmosphere.
Researchers have discovered a previously unrecognized process involving semi-volatile gases produced by plants in the Amazon rainforest and transported into the upper atmosphere by clouds. These gases are natural carbon-based chemical compounds that condense easily in the upper atmosphere to create fine particles. Shrivastava states that this method is particularly effective in producing fine particles at high altitudes and low temperatures. These fine particles cool the earth by reducing the amount of sunlight that reaches it. They also produce clouds, which affect rainfall and the water cycle.
“Without a full understanding of the semi-volatile source of organic gas, we simply cannot explain the presence and role of key particles at high altitudes,” Shrivastava said.
Crucial discovery in atmospheric processes
Shrivastava’s research project, funded by the Department of Energy’s (DOE) Early Career Research Award, involved investigating the formation of aerosol particles known as IOSPOX-SOA epoxidiol isoprene secondary organic aerosols, which are measured by airplanes flying at different altitudes.
IEPOX-SOA are essential blocks 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 altitude above the tropics. However, atmospheric patterns did not take sufficient account of these particles and their influence on clouds above the Earth.
“Because the models would not predict the IEPOX-SOA loads observed at altitudes of 10 to 14 kilometers in the Amazon, I received what I thought was either a malfunction of the model or a lack of understanding of the measurements,” said Shrivastava. “I could explain that on the surface, but I couldn’t explain it at higher altitudes.”
Shrivastava and his team investigated data collected by the Grumman Gulfstream-159 (G-1) aircraft, a DOE flight laboratory operated by the Airborne Atmospheric Radiation (ARM) facility, which flew at an altitude of up to 5 kilometers. The team also compared data collected by a German aircraft known as High Altitude and Long Range Research Aircraft, or HALO, which flies at altitudes of up to 14 kilometers. Based on the modeled projections, their IEPOX-SOA loads should have been at least an order of magnitude smaller than what was measured, Shrivastava said. Neither he nor his colleagues outside the PNNL could explain the difference in measurements and what the models designed.
Prior to the team’s research, it was believed that IEPOX-SOAs were formed primarily through multiphase atmospheric chemistry involving isoprene reactions in the gas phase and particles containing liquid water. However, the atmospheric chemical pathways required to create IEPOX-SOA do not occur in the upper troposphere due to its extremely cold temperatures and dry conditions. At that altitude, the particles and clouds are frozen and lack liquid water. Therefore, the researchers could not explain their observed formation at 10 to 14 kilometers altitude using the available models.
To unravel the mystery, the researchers combined specialized measurements of high-altitude airplanes and detailed simulations of regional models performed using supercomputing resources at the PNNL’s Laboratory of Molecular Environmental Sciences. Their study of r