The Amazon rainforest and its role in cloud formation through plant emissions and thunderstorms

The Amazon rainforest and its role in cloud formation through plant emissions and thunderstorms
by Robert Schreiber
Berlin, Germany (SPX) Dec 06, 2024

The distinctive scent of forests, often associated with summer walks, originates partly from terpenes - compounds found in tree resins and essential oils. A dominant terpene molecule, isoprene, is released in enormous quantities by plants globally, with estimates of 500 to 600 million tons annually. Atmospheric researcher Professor Joachim Curtius of Goethe University Frankfurt explains, "The Amazon rainforest alone accounts for over a quarter of these emissions."

Previously, scientists believed isoprene in the Amazon basin degraded rapidly due to interactions with hydroxyl radicals formed during daytime sunlight exposure. However, recent findings reveal that significant amounts of isoprene persist through the night and can ascend to higher atmospheric layers.

Thunderstorms as transport mechanisms

Nighttime thunderstorms over the Amazon function as "vacuum cleaners," drawing isoprene to altitudes of 8 to 15 kilometers. There, under extremely low temperatures, the molecules undergo transformations distinct from ground-level reactions. When combined with nitrogen oxides generated by lightning, they form clusters that evolve into aerosol particles. These particles serve as condensation nuclei, fostering water vapor condensation and contributing to tropical cloud formation.

Research led by Professor Jos Lelieveld, director at the Max Planck Institute for Chemistry and head of the CAFE-Brazil project (Chemistry of the Atmosphere: Field Experiment in Brazil), employed pre-dawn research flights to observe these phenomena. "We detected substantial amounts of isoprene at high altitudes in thunderstorm outflows, where they rapidly formed new aerosol particles after several chemical reactions," Lelieveld noted.

Implications for oceanic cloud systems

The researchers' collaboration extends to the CLOUD consortium, involving over 20 research groups studying atmospheric chemical processes at CERN in Geneva. Using the aerosol and cloud experiment chamber, they replicated high-altitude conditions to examine sunlight-triggered reactions. Atmospheric researcher Dr. Xu-Cheng He, who oversees the isoprene experiments, explained, "Even minute amounts of sulfuric acid and iodine oxoacids accelerate aerosol particle formation by a factor of 100, which could influence marine cloud formation - a major uncertainty in climate models."

High-altitude winds can transport these isoprene-derived particles thousands of kilometers from their Amazonian origins, potentially affecting cloud formation in distant regions. Since clouds play a dual role in climate regulation - shielding solar radiation and trapping heat - the findings could enhance climate modeling accuracy.

The dual impact of deforestation

The CAFE-Brazil findings underscore the critical link between Amazon deforestation and climate dynamics. Curtius highlighted two key effects: "Deforestation releases greenhouse gases by eliminating carbon dioxide storage and disrupts water cycles and isoprene emissions, accelerating climate change."

Research Report:Isoprene nitrates drive new particle formation in Amazon's upper troposphere