(1) Royal Netherlands Meteorological Institute, De Bilt, The Netherlands (veefkind@knmi.nl), (2) Delft University of Technology, Geosciences and Remote Sensing, Delft, The Netherlands, (3) Netherlands Institute for Space Research, Utrecht, The Netherlands, (4) European Space Research Institute, Frascati, Italy, (5) German Aerospace Center, Wessling, Germany, (6) European Space Research and Technology Centre, Noordwijk, The Netherlands, (7) University of Bremen, Bremen, Germany, (8) Belgian Institute for Space Aeronomy, Brussels, Belgium, (9) Rutherford Appleton Laboratory, Didcot, United Kingdom, (10) Max Planck Institute for Chemistry, Mainz, Germany