Collaborative Research: Cosmics Leaving OUtdoor Droplets (CLOUD) Consortium Membership

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This project supports the continued membership in the CLOUD consortium at CERN, by Carnegie-Mellon University and the California Institute of Technology, and provides new membership for the University of Colorado at Boulder. The CLOUD (Cosmics Leaving OUtdoor Droplets) experimental facility is likely the world's most sophisticated experiment addressing atmospheric new-particle formation. It was constructed to measure new particle formation under highly controlled, ultra-clean conditions.CLOUD is an international member-funded consortium supporting the maintenance and operation of the experiment. Members raise research funding from their national agencies to participate. Experiments are conducted at CERN during 1-2 carefully planned campaigns per year, each lasting 8-10 weeks. These campaigns are planned, and data are assessed, during two major week-long consortium meetings each year, while more focused, intensive data analysis is carried out at all times by individuals, but also in several focused team meetings scheduled and hosted on an ad-hoc basis during the course of each year as analysis and interpretation require. Virtual team meetings via skype and other media are ongoing and continuous.In addition to providing the required consortium fee, this project will support shipping and travel to CLOUD experimental campaigns and associated consortium meetings and data workshops. The doctoral and postdoctoral students associated with the project will be integrated into an international collaborative network of students and senior researchers who are among the most highly regarded in aerosol science and atmospheric chemistry. They will receive invaluable training in the conduct of international collaborative research.The subject of the CLOUD experiments is of high national and international interest. Aerosol-cloud interactions are among the largest sources of uncertainty in the understanding of climate forcing and climate sensitivity. CLOUD experiments confirm that ions can stabilize nucleating clusters, and that, for otherwise weakly bound clusters (such as ammonia sulfuric acid, organics with sulfuric acid, and pure organics), ions can enhance nucleation rates by factors of 3-100 depending on conditions. During the period of this project, three campaigns, CLOUD-13, CLOUD-14, and CLOUD-15, are planned. The campaigns will focus on the following broad topics: the role of organic oxidation chemistry in new-particle formation and growth; new-particle formation in urban areas; new-particle formation in the marine atmosphere; and the role, if any, of charge in cloud-droplet formation and ice-crystal nucleation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.