1. Department of Geology and Geoenvironment, National and Kapodistrian University of Athens, GR-15784 Athens, Greece
2. Biomedical Research Foundation of the Academy of Athens, GR-11527 Athens, Greece
3. Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, 7260 Davos Dorf, Switzerland
4. Research Centre for Atmospheric Physics and Climatology, Academy of Athens, GR-11521 Athens, Greece
5. Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, Penteli, GR-15236 Athens, Greece
6. Institute for Environmental Research & Sustainable Development, National Observatory of Athens, Penteli, GR-15236 Athens, Greece
7. Laboratory of Atmospheric Physics, Department of Physics, University of Patras, GR-26500 Patras, Greece
8. Institute of Environmental Physics, Universität Bremen, D-28359 Bremen, Germany