title: From hygroscopic aerosols to cloud droplets: The HygrA-CD campaign in the Athens basin - An overview.
abstract: The international experimental campaign Hygroscopic Aerosols to Cloud Droplets (HygrA-CD), organized in the Greater Athens Area (GAA), Greece from 15 May to 22 June 2014, aimed to study the physico-chemical properties of aerosols and their impact on the formation of clouds in the convective Planetary Boundary Layer (PBL). We found that under continental (W-NW-N) and Etesian (NE) synoptic wind flow and with a deep moist PBL (~2-2.5km height), mixed hygroscopic (anthropogenic, biomass burning and marine) particles arrive over the GAA, and contribute to the formation of convective non-precipitating PBL clouds (of ~16-20μm mean diameter) with vertical extent up to 500m. Under these conditions, high updraft velocities (1-2ms-1) and cloud condensation nuclei (CCN) concentrations (~2000cm-3at 1% supersaturation), generated clouds with an estimated cloud droplet number of ~600cm-3. Under Saharan wind flow conditions (S-SW) a shallow PBL (<1-1.2km height) develops, leading to much higher CCN concentrations (~3500-5000cm-3at 1% supersaturation) near the ground; updraft velocities, however, were significantly lower, with an estimated maximum cloud droplet number of ~200cm-3and without observed significant PBL cloud formation. The largest contribution to cloud droplet number variance is attributed to the updraft velocity variability, followed by variances in aerosol number concentration.
authors.affiliation: Laser Remote Sensing Unit, Physics Department, School of Applied Mathematics and Physical Sciences, National Technical University of Athens, 15780 Zografou, Greece. Electronic address: apdlidar@central.ntua.gr.
authors.forename: A
authors.initials: A
authors.lastname: Papayannis
authors.affiliation: Laser Remote Sensing Unit, Physics Department, School of Applied Mathematics and Physical Sciences, National Technical University of Athens, 15780 Zografou, Greece.
authors.forename: A
authors.initials: A
authors.lastname: Argyrouli
authors.affiliation: Laser Remote Sensing Unit, Physics Department, School of Applied Mathematics and Physical Sciences, National Technical University of Athens, 15780 Zografou, Greece; School of Earth & Atmospheric Sciences, Georgia Institute of Technology, Atlanta 30332, GA, USA.
authors.forename: A
authors.initials: A
authors.lastname: Bougiatioti
authors.affiliation: Laboratory of Environmental Science and Engineering, School of Mining and Metallurgical Engineering, National Technical University of Athens, 15780 Zografou, Greece.
authors.forename: E
authors.initials: E
authors.lastname: Remoundaki
authors.affiliation: Laser Remote Sensing Unit, Physics Department, School of Applied Mathematics and Physical Sciences, National Technical University of Athens, 15780 Zografou, Greece; ERL, INRSTES, N.C.S.R. Demokritos, 15310 Agia Paraskevi, Attiki, Greece.
authors.forename: S
authors.initials: S
authors.lastname: Vratolis
authors.affiliation: School of Earth & Atmospheric Sciences, Georgia Institute of Technology, Atlanta 30332, GA, USA; ICE-HT, Foundation for Research and Technology, Hellas, 26504 Patras, Greece; Institute of Environmental Research and Sustainable Development, National Observatory of Athens, Athens, Greece; School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta 30332, GA, USA.
authors.forename: A
authors.initials: A
authors.lastname: Nenes
authors.affiliation: Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, Athens, Greece.
authors.forename: S
authors.initials: S
authors.lastname: Solomos
authors.affiliation: Finnish Meteorological Institute, Kuopio, Finland.
authors.forename: M
authors.initials: M
authors.lastname: Komppula
authors.affiliation: Finnish Meteorological Institute, Kuopio, Finland; Department of Environmental Physics and Meteorology, Faculty of Physics, University of Athens, Athens, Greece.
authors.forename: E
authors.initials: E
authors.lastname: Giannakaki
authors.affiliation: Institute of Environmental Research and Sustainable Development, National Observatory of Athens, Athens, Greece.
authors.forename: J
authors.initials: J
authors.lastname: Kalogiros
authors.affiliation: Barcelona Supercomputing Center-Centro Nacional de Supercomputación (BSC-CNS), Earth Sciences Department, Jordi Girona 29, Edificio Nexus II, Barcelona, Spain; Environmental Modelling Laboratory, Polytechnic University of Catalonia, Barcelona, Spain.
authors.forename: R
authors.initials: R
authors.lastname: Banks
authors.affiliation: ERL, INRSTES, N.C.S.R. Demokritos, 15310 Agia Paraskevi, Attiki, Greece.
authors.forename: K
authors.initials: K
authors.lastname: Eleftheriadis
authors.affiliation: Laboratory of Environmental Science and Engineering, School of Mining and Metallurgical Engineering, National Technical University of Athens, 15780 Zografou, Greece.
authors.forename: E
authors.initials: E
authors.lastname: Mantas
authors.affiliation: ERL, INRSTES, N.C.S.R. Demokritos, 15310 Agia Paraskevi, Attiki, Greece.
authors.forename: E
authors.initials: E
authors.lastname: Diapouli
authors.affiliation: Climate Research Group, Division of Environmental Physics and Meteorology, Department of Physics, National and Kapodistrian University of Athens, 15784 Athens, Greece.
authors.forename: C G
authors.initials: CG
authors.lastname: Tzanis
authors.affiliation: Institute of Environmental Research and Sustainable Development, National Observatory of Athens, Athens, Greece; Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, Switzerland.
authors.forename: S
authors.initials: S
authors.lastname: Kazadzis
authors.affiliation: National Institute of Research and Development for Optoelectronics, Magurele, Romania.
authors.forename: I
authors.initials: I
authors.lastname: Binietoglou
authors.affiliation: National Institute of Research and Development for Optoelectronics, Magurele, Romania; Research Center of Ecological Safety, Russian Academy of Sciences, St. Petersburg, Russia.
authors.forename: L
authors.initials: L
authors.lastname: Labzovskii
authors.affiliation: Department of Physics and Astronomy, Earth Observation Science Group, University of Leicester, University Road, Leicester LE1 7RH, UK.
authors.forename: J
authors.initials: J
authors.lastname: Vande Hey
authors.affiliation: Biomedical Research Foundation of the Academy of Athens, Athens, Greece; Navarino Environmental Observatory (N.E.O.), Messinia, Greece.
authors.forename: C S
authors.initials: CS
authors.lastname: Zerefos
keywords: Aerosol Raman lidar; Aerosol chemical properties; Athens; CCN; Cloud development; Cloud droplet number; Doppler lidar; FLEXPART model; Greece; HygrA-CD; Precipitation radar; SMPS; WRF