A Large Source of Cloud Condensation Nuclei from New Particle Formation in the Tropics

• Published in: Nature (London) Vol. 574; no. 7778; pp. 399 - 403
• Main Authors: Williamson, Christina J, Kupc, Agnieszka, Axisa, Duncan, Bilsback, Kelsey R, Bui, ThaoPaul, Campuzano-Jost, Pedro, Dollner, Maximilian, Froyd, Karl D, Hodshire, Anna L, Jimenez, Jose L, Kodros, John K, Luo, Gan, Murphy, Daniel M, Nault, Benjamin A, Ray, Eric A, Weinzierl, Bernadett, Wilson, James C, Yu, Fangqun, Yu, Pengfei, Brock, Charles A
• Format: Journal Article
• Language: English
• Published: 2230 Support Nature Research 01.10.2019; Nature Publishing Group UK; Nature Publishing Group
• Subjects: 704/106/35/824; 704/106/694/1108; 704/172/169/824; Aerosols; Aircraft; Atlantic Ocean; Atmosphere; Atmospheric models; Cloud condensation nuclei; Cloud formation; Cloud properties; Clouds; Condensates; Condensation; Condensation nuclei; Earth surface; High-altitude environments; Humanities and Social Sciences; Letter; Lower troposphere; Meteorology and Climatology; Models, Chemical; multidisciplinary; Natural history; Ocean models; Oceans; Organic chemistry; Pacific Ocean; Particle formation; Particle size; Particulate Matter; Science; Science & Technology - Other Topics; Science (multidisciplinary); Tropical Climate; Tropical environments; Tropics; Troposphere; Upper troposphere; Atlantic Ocean; Pacific Ocean; United States; United States > US; Atmospheric Chemistry; Climate And Earth System Modelling
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/s41586-019-1638-9

Cloud condensation nuclei (CCN) can affect cloud properties and therefore the Earth’s radiative balance. New particle formation (NPF) from condensable vapours in the free troposphere has been suggested to contribute to CCN, especially in remote, pristine atmospheric regions, but direct evidence is sparse, and the magnitude of this contribution is uncertain. Here we use in-situ aircraft measurements of vertical profiles of aerosol size distributions to present a global-scale survey of NPF occurrence. We observed intense NPF occurring at high altitude in tropical convective regions over both the Pacific and Atlantic Oceans. Together with the results of chemical-transport models, our findings indicate that NPF persists at all longitudes as a global-scale band in the tropical upper troposphere, covering about 40% of the Earth’s surface. Furthermore, we find that this NPF in the tropical upper troposphere is a globally important source of CCN in the lower troposphere, where they can affect cloud properties. Our findings suggest that the production of CCN, as these new particles descend towards the surface, is currently not adequately captured in global models, because they tend to underestimate both the magnitude of tropical upper tropospheric NPF and the subsequent growth to CCN sizes. This has potential implications for cloud albedo and the global radiative balance.