Milena Horvat¹, Igor Zivkovic¹, Jan Gacnik¹, Joze Kotnik¹, Sergio Ribeiro Guevara², Ina Fettig³, Timo Rajamaki⁴, Panayot Petrov⁵, Iris de Krom⁶, David P Amouroux⁷, Emmanuel Tessier⁷, Olivier Donard⁷, Maria del Rocio Arvizu⁸, Jarkko Makkonen⁹, Warren Corns¹⁰, Ian M Hedgecock¹¹, Attilio Naccarato¹², Nicola Pirrone¹², Francesca Sprovieri¹¹, Reinhold Moeseler¹³ and Suleyman Can¹⁴, (1)Jozef Stefan Institute, Ljubljana, Slovenia, (2)Centro Atomico Bariloche, Bariloche, Argentina, (3)UBA German Federal Environment Agency, Berlin, Germany, (4)VTT Tech Research Centre, Espoo, Finland, (5)LGC, Teddington, United Kingdom, (6)Dutch Metrology Institute, Delft, Netherlands, (7)IPREM / CNRS, Pau, France, (8)Centro Nacional de Metrología, Municipio El Marqués, Mexico, (9)Optoseven, Espoo, Finland, (10)P S Analytical, Orpington, United Kingdom, (11)CNR Institute of Atmospheric Pollution Research, Rende, Italy, (12)CNR Institute of Atmospheric Pollution Research, Prato, Italy, (13)Lumex Analytics, Wakendorf, Germany, (14)TÜBİTAK National Metrology Institute, Gebze, Turkey