- Aarhus University [Aarhus]
- ABB Bomem Inc.
- Abdou Moumouni University of Niamey = Université Abdou Moumouni de Niamey
- Abdus Salam International Centre for Theoretical Physics [Trieste]
- Aberystwyth University
- ABR, Inc. - Environmental Research and Services
- Academy of Athens
- Addis Ababa University
- Aerospatiale Inc.
- Agence Spatiale Européenne = European Space Agency
- Agencia Estatal de Meteorología
- Agenzia Nazionale per le nuove Tecnologie, l’energia e lo sviluppo economico sostenibile = Italian National Agency for New Technologies, Energy and Sustainable Economic Development
- AGROCAMPUS OUEST
- AgroParisTech
- Air Force Geophysics Laboratory
- Air Force Research Laboratory
- AIRMARAIX
- AIRPARIF - Surveillance de la qualité de l'air en Île-de-France
- Air Quality Research Division [Toronto]
- AIT Advanced Information Technologies Corporation
- Aix Marseille Université
- ALCATEL
- ALCATEL SPACE
- Alfred Wegener Institute for Polar and Marine Research
- Alfred Wegener Institute [Potsdam]
- Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung = Alfred Wegener Institute for Polar and Marine Research = Institut Alfred-Wegener pour la recherche polaire et marine
- Allied Signal Corporation
- Alma Mater Studiorum Università di Bologna = University of Bologna
- Ambiances architecturales et urbaines
- A.M.Obukhov Institute of Atmospheric Physics
- AMOS
- Analytical Services and Materials, Inc.
- Analytic and Computational Research, Inc. - Earth Sciences
- Andøya Rocket Range
- Anglo-Australian Observatory
- APC - Cosmologie
- Applied Marine Physics [Miami]
- Arctic Research Centre of Finnish Meteorological Institute
- Argelander-Institut für Astronomie
- Argentière
- Argonne National Laboratory [Lemont]
- Aristotle University of Thessaloniki
- Armagh Observatory [Armagh]
- ARPA Emilia-Romagna, Agenzia Regionale per la Protezione dell’Ambiente
- ARQM Meteorological Service Canada
- Array Systems Computing
- Arrhenius Laboratory
- Association of Universities for Research in Astronomy
- ASTRIUM
- Astrium SAS
- Astrium Satellites
- Astrium [Stevenage]
- Astrium [Toulouse]
- Astronomical Institute Anton Pannekoek
- Astronomical Institute of Kharkiv Karazin National University
- Astronomical observatory of Odessa National University [Odessa]
- Astronomie et systèmes dynamiques
- Astronomisches Institut der Ruhr-Universität Bochum
- Astronomy Unit [London]
- AstroParticule et Cosmologie
- Astrophysics Research Centre [Belfast]
- Astrophysikalisches Institut Potsdam
- Astrophysique Interprétation Modélisation
- Atmospheric and Environmental Research, Inc.
- Atmospheric and Oceanic Sciences Program [Princeton]
- Atmospheric Chemistry and Dynamics Laboratory [ Greenbelt]
- Atmospheric Chemistry Division [Boulder]
- Atmospheric Chemistry Modelling Support Unit [Cambridge]
- Atmospheric Physics Laboratory [UCL London]
- Atmospheric Sciences Division [Hampton]
- Atmospheric Systems and Analysis [Westminster]
- ATMOS Sarl
- Australian Antarctic Division
- Australian Bureau of Meteorology [Melbourne]
- Australian Centre for Astrobiology
- Australian Government
- Australian Government, Department of the Environment and Energy
- Austrian Academy of Sciences
- Avant création Cerema
- Avignon Université