Vilma Kangasaho¹, Aki Tsuruta¹, Tuula Aalto¹, Leif Bjarne Backman¹, Sander Houweling², Maarten C Krol^3,4, Wouter Peters^5,6, Ingrid Theodora van der Laan-Luijkx⁴, Sebastian Lienert⁷, Fortunat Joos⁸, Edward J Dlugokencky⁹, Sylvia Michel¹⁰, James W C White¹¹ and Rebecca Fisher¹², (1)Finnish Meteorological Institute, Helsinki, Finland, (2)SRON, Netherlands Institute for Space Research, Utrecht, Netherlands, (3)Netherlands Institute for Space Research, Utrecht, Netherlands, (4)Wageningen University and Research, Wageningen, Netherlands, (5)Wageningen University, Wageningen, Netherlands, (6)University of Groningen, Groningen, Netherlands, (7)University of Bern, Climate and Environmental Physics, Bern, Switzerland, (8)Univ Bern, Climate and Environmental Physics, Bern, Switzerland, (9)NOAA/ESRL Global Monitoring Division, Boulder, CO, United States, (10)Institute of Arctic and Alpine Research, Geological Sciences, Boulder, CO, United States, (11)Univ Colorado, Institute of Arctic and Alpine Research, Boulder, CO, United States, (12)Royal Holloway, University of London, Egham, United Kingdom