Arnoud Apituley¹, Karin Kreher², Michael Van Roozendael³, John Sullivan⁴, Thomas J McGee⁴, Marc Allaart¹, Ankie Piters¹, Deborah C Stein¹, Henk Eskes¹, J. S. Henzing⁵, Tim Vlemmix¹, Bryan de Goeij⁶, Herman W.J. Russchenberg⁷, Ronald W A Hutjes⁸, Joris P Veefkind¹, Larry Twigg⁴, Grant K. Sumnicht⁴, Arnoud Frumau⁹, Jan Vonk¹⁰, Mirjam den Hoed¹ and Christine Unal⁷, (1)Royal Netherlands Meteorological Institute, De Bilt, Netherlands, (2)BK Scientific, Mainz, Germany, (3)Royal Belgian Institute for Space Aeronomy, Brussels, Belgium, (4)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (5)Netherlands Organization for Applied Scientific Research, Utrecht, Netherlands, (6)Netherlands Organization for Applied Scientific Research, The Hague, Netherlands, (7)Delft University of Technology, Delft, Netherlands, (8)Wageningen University, Wageningen, Netherlands, (9)TNO, Utrecht, Netherlands, (10)National Institute for Public Health and the Environment, Bilthoven, Netherlands