Formation Process of Particles and Cloud Condensation Nuclei Over the Amazon Rainforest: The Role of Local and Remote New-Particle Formation

Understanding the formation processes of particles and cloud condensation nuclei (CCN) in pristine environments is a major challenge in assessing the anthropogenic impacts on climate change. Using a state-of-the-art model that systematically simulates the new-particle formation (NPF) from condensable vapors and multi-scale transport of chemical species, we find that NPF contributes similar to 90% of the particle number and similar to 80% of the CCN at 0.5% supersaturation (CCN0.5%) in the pristine Amazon boundary layer during the wet season. The corresponding contributions are only similar to 30% and similar to 20% during the dry season because of prevalent biomass burning. In both seasons, similar to 50% of the NPF-induced particles and similar to 85% of the NPF-induced CCN0.5% in the boundary layer originate from the long-range transport of new particles formed hundreds to thousands of kilometers away. Moreover, about 50%-65% of the NPF-induced particles and 35%-50% of the NPF-induced CCN0.5% originate from the downward transport of new particles formed aloft.

Automated summary

Understanding the formation processes of particles and cloud condensation nuclei (CCN) in pristine environments is crucial for assessing anthropogenic impacts on climate change. This study used a sophisticated model to simulate the formation of new particles from condensable vapors and the transport of chemical species. The results showed that the new particle formation plays a significant role in the particle and CCN concentrations in the pristine Amazon boundary layer. These new particles mainly originate from long-range transport and downward transport from the upper atmosphere.