An international group of researchers, with emphasis on the participation of Brazilians, managed to unveil the physical-chemical mechanism that explains the complex rain formation system in the Amazon with influence on the global climate.
The system involves the production of aerosol nanoparticles, electrical discharges and chemical reactions at high altitudes, occurring between night and day, resulting in a kind of aerosol machine that will produce clouds.
The research, published this Wednesday (4) on the cover of Nature magazinedescribes the mechanisms of how isoprene — a gas released by vegetation through its metabolism — is transported to the layer of the atmosphere above the Earth’s surface near the tropopause during nighttime storms.
A series of chemical reactions triggered by solar radiation gives rise to a large amount of aerosols that form clouds.
This particle production is accelerated by reactions with nitrogen oxides produced by electrical discharges in the upper atmosphere, in clouds dominated by ice crystals.
Until then, scientists had already identified the particles in another expedition, but not the complete physical-chemical mechanism.
It was believed that isoprene would not reach the upper layers of the atmosphere because it would react along the way, as it is quite reactive, and would degrade quickly in sunlight.
With the discovery of these new mechanisms, it will be possible to improve models of the Earth system, fundamental tools for simulating the climate and understanding the present and future functioning of the planet.
To reach the result, the group used material obtained during the scientific experiment Cafe-Brazil, an acronym in English for Chemistry of the Atmosphere: Field Experiment in Brazil.
The only one of its kind, the experiment carried out several flights over the Amazon basin between December 2022 and January 2023, at an altitude of 14 kilometers, which corresponds to twice the height of Aconcagua, the highest point in South America.
It totaled 136 hours of flight, covering 89,000 km — more than two complete trips around the Earth around the Equator.
“One of the highlights of this work is seeing how the Amazon has a symbiosis of complex mechanisms and important phenomena that act within a sensitive ecosystem balance. Preserving this balance allows us to maintain climate conditions as we know them today. Changes such as those caused by climate change or deforestation can generate unexpected effects that have not yet been studied”, explains to Agência Fapesp one of the Brazilian authors of the research, professor Luiz Augusto Toledo Machado.
Researcher at the Physics Institute of the University of São Paulo (IF-USP) and collaborator in the Chemistry Department of the Max Planck Institute, in Germany, Machado says that the result opens a broad horizon to analyze the impact of global warming on the climate, in the environment environment and ecosystem.
For Paulo Artaxo, coordinator of the Center for Sustainable Amazon Studies (Ceas) at USP, professor at IF-USP and co-author of the article, the results allow modeling to be carried out more reliably, and may include mechanisms from a physical-chemical and biological point of view.
“Isoprene emissions depend on the standing forest. They do not occur if native vegetation is replaced by pasture or soybean crops. With deforestation, this particle production mechanism is destroyed, reducing the formation of clouds and precipitation. This is what we call negative feedback in the total climate system, as deforestation significantly reduces precipitation by reducing evapotranspiration and particle production, which depend on isoprene emissions”, says Artaxo.
A survey released by MapBiomas in October, based on satellite images, showed that pasture was the main purpose of deforestation in the Amazon between 1985 and 2023.
During the period, this area grew by more than 363%, going from around 12.7 million to 59 million hectares. As a result, 14% of the Amazon had become pasture area by 2023.
The mechanism
The forest exudes very characteristic aromas.
These are gases known as volatile organic compounds (VOCs), including terpenes — a group of substances found in tree resins and essential oils — and isoprene.
It is estimated that forests around the world release more than 500 million tons of isoprene into the atmosphere annually, with a quarter of this emission coming from the Amazon.
In the Amazon rainforest, isoprene is emitted during the day as it depends on sunlight.
It was believed that the gas did not reach the highest layers of the atmosphere because it would be destroyed within a few hours by highly reactive hydroxyl radicals.
“Now we have established that this is partially true. There is still a considerable amount of isoprene at night. A significant part of these molecules can be transported to higher layers of the atmosphere”, states in a note the corresponding author of the article, Joachim Curtius, professor at Goethe University in Frankfurt, Germany.
During the night, tropical storms over the forest help transport gases, such as isoprene, to higher layers through intense convection.
Similar to a vacuum cleaner, this process is driven by upward air currents, especially in regions with high humidity and accumulated heat.
The gases combine with nitrogen compounds from lightning in the upper atmosphere.
In the highest areas, between 8 km and 15 km above sea level, temperatures reach minus 60°C.
About two hours after sunrise, the hydroxyl radicals that also form at these altitudes react with isoprene, giving rise to organic nitrates, compounds different from those found near the ground.
They therefore produce high concentrations of aerosol nanoparticles, with more than 50 thousand of them per cubic centimeter.
These particles grow over time and are transported over long distances, and can act as cloud condensation nuclei. They influence the global hydrological cycle, the radiation balance and the climate.
The formation mechanisms of these organic nitrogen compounds will now be incorporated into climate models, improving rainfall forecasts, especially in tropical regions.
Fapesp supports the study through a Thematic Project linked to the Research Program on Global Climate Change (PFPMCG) and led by Machado and another by Artaxo, in addition to four other projects.
In addition to this research, the journal Nature brings in the same edition another study developed by the team of researchers that deals with the new formation of particles from isoprene in the upper troposphere.
They reproduce the conditions present at these altitudes in experimental chambers, analyzing in detail the reactions triggered by sunlight.
The expedition
Several research flights carried out in the Cafe-Brazil experiment contributed to the generation of altitude profiles for different gases.
It was possible to measure air masses transported to the upper troposphere and the differences between daytime and nighttime situations.
Professor Machado, who participated in collecting information in the Amazon, says that flights could last up to 12 hours.
“We stayed all night. We noticed that the particles formed in the morning. That’s why we left early in the morning. The teams went to the airport to fly, while I and other researchers stayed in the operations room monitoring and giving guidance on the forecasts and where the rain was. I also did flights that went into the clouds to measure isoprene. It was very exciting”, he says.
The work base was set up in Manaus (AM). The flights were carried out with the HALO plane (acronym in English for High Altitude and Long range research aircraft), a research aircraft for long distances (more than 8,000 km), high altitudes (up to 15.5 km) and large loads (up to three tons).
The experiment was a partnership between the Goethe University of Frankfurt, the Max Planck Institute of Chemistry (Germany), the National Institute for Space Research (Inpe) — which was responsible for licensing the scientific expedition coordinated by researcher Dirceu Herdies, also author of article –, the National Institute for Amazonian Research (Inpa) and USP.
This content was originally published in Complex Amazon rain system is revealed on the CNN Brasil website.
Source: CNN Brasil
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