Isoprene nitrates drive aerosol formation in the upper atmosphere in the tropics
In a major scientific breakthrough, researchers from the Department of Environmental Science at Stockholm University have been at the forefront of uncovering the critical role of isoprene nitrates in forming new particles in the upper troposphere over the Amazon rainforest.
This discovery was published recently across three interconnected studies, two in Nature and one in Geophysical Research Letters. The Stockholm University researchers were co-authors in the Nature papers and lead authors of the Geophysical Research Letters study.
Clouds play a pivotal role in Earth's climate system, reflecting sunlight and influencing global weather patterns. The formation of these clouds relies on tiny particles known as cloud condensation nuclei, which can originate from both human activities, like pollution, and natural processes, such as emissions from plants. As cleaner air policies are implemented worldwide, the significance of these natural processes is expected to grow.
The research emphasizes how naturally occurring chemicals released by plants, particularly isoprene nitrates, play a crucial role in cloud formation—an impact that will become increasingly significant as manmade aerosols decline. The team at Stockholm University led the theoretical work that connected laboratory findings to atmospheric observations, offering key insights into these complex atmospheric phenomena.
The role of isoprene in cloud formation
Isoprene, a volatile organic compound (VOC) released in vast quantities by trees and plants, especially in the Amazon, rises into the atmosphere and reacts with nitrogen oxides (NOx) produced by lightning. This reaction forms isoprene nitrates, compounds now understood to be critical in particle formation at high altitudes (8-12 km above sea level). Previously, it was thought that other VOCs like monoterpenes were the dominant contributors to new particle formation in the Amazon. However, the new findings have shifted this perspective.
"Our simulations reveal that when isoprene-derived compounds, including isoprene nitrates, are factored into the process, particle formation rates soar by six orders of magnitude, matching observed concentrations over the Amazon. This shows that isoprene nitrates possess the properties necessary to form cloud-seeding nanoparticles," explains Roman Bardakov, postdoctoral researcher at the Department of Environmental Science and lead author of the Geophysical Research Letters study.
Collaborative research effort
These findings are part of a larger collaborative effort to unravel the process of cloud formation and its impact on climate. The two additional studies, published in Nature this week, also feature the Stockholm University researchers and further support the groundbreaking conclusions. These studies include:
• The CAFE-Brazil aircraft campaign, where researchers identified isoprene nitrates as the trigger for particle bursts in the upper atmosphere, caused by lightning-generated nitrogen oxides.
• The CERN CLOUD chamber experiments, where scientists recreated atmospheric conditions to demonstrate that isoprene oxidation products can initiate new particle formation.
Together, these three studies underscore the vital role that natural compounds like isoprene nitrates play in shaping weather patterns and cloud formation, with implications for global climate models.
“These exciting findings open new avenues for exploring how tropical ecosystems influence global climate,” adds Ilona Riipinen, Professor at the Department of Environmental Science and Director of the Bolin Centre for Climate Research, who led the Stockholm University efforts. “As we continue to tackle climate change and reduce pollution, understanding these natural processes becomes ever more critical.”
Read the scientific articles:
Shen, J., et al., (2024). New particle formation from isoprene in the upper troposphere. Nature
Last updated: December 5, 2024
Source: Department of Environmental Science