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CCN Activity, Variability and Influence on Droplet Formation during the HygrA-Cd Campaign in Athens

School of Earth & Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA
Laser Remote Sensing Laboratory, National Technical University of Athens, Athens 15780, Greece
Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing (IAASARS), National Observatory of Athens, Athens 15236, Greece
Environmental Radioactivity Laboratory, Institute of Nuclear & Radiological Sciences & Technology, Energy & Safety, National Centre For Scientific Research Demokritos, Ag. Paraskevi, Athens 15310, Greece
School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
Institute for Environmental Research and Sustainable Development, National Observatory of Athens, P. Penteli, Athens 15236, Greece
Institute for Chemical Engineering Sciences, Foundation of Research and Technology Hellas, Patras 26504, Greece
Authors to whom correspondence should be addressed.
Academic Editor: Jessie M. Creamean
Atmosphere 2017, 8(6), 108;
Received: 9 April 2017 / Revised: 23 May 2017 / Accepted: 14 June 2017 / Published: 19 June 2017
(This article belongs to the Special Issue Atmospheric Aerosol Composition and its Impact on Clouds)
PDF [1785 KB, uploaded 19 June 2017]


Measurements of cloud condensation nuclei (CCN) concentrations (cm−3) at five levels of supersaturation between 0.2–1%, together with remote sensing profiling and aerosol size distributions, were performed at an urban background site of Athens during the Hygroscopic Aerosols to Cloud Droplets (HygrA-CD) campaign. The site is affected by local emissions and long-range transport, as portrayed by the aerosol size, hygroscopicity and mixing state. Application of a state-of-the-art droplet parameterization is used to link the observed size distribution measurements, bulk composition, and modeled boundary layer dynamics with potential supersaturation, droplet number, and sensitivity of these parameters for clouds forming above the site. The sensitivity is then used to understand the source of potential droplet number variability. We find that the importance of aerosol particle concentration levels associated with the background increases as vertical velocities increase. The updraft velocity variability was found to contribute 58–90% (68.6% on average) to the variance of the cloud droplet number, followed by the variance in aerosol number (6–32%, average 23.2%). Therefore, although local sources may strongly modulate CCN concentrations, their impact on droplet number is limited by the atmospheric dynamics expressed by the updraft velocity regime. View Full-Text
Keywords: CCN activity; droplet formation; cloud maximum supersaturation; relative contribution of updraft velocity CCN activity; droplet formation; cloud maximum supersaturation; relative contribution of updraft velocity

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Bougiatioti, A.; Argyrouli, A.; Solomos, S.; Vratolis, S.; Eleftheriadis, K.; Papayannis, A.; Nenes, A. CCN Activity, Variability and Influence on Droplet Formation during the HygrA-Cd Campaign in Athens. Atmosphere 2017, 8, 108.

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