We are indebted to the site operators who oversee the day-to-day running of the AGAGE, NIES and NOAA stations. We particularly thank the NASA Upper Atmosphere Research Program for its continuing support of AGAGE, including providing modelling, field station and instrumentation support though grant NNX16AC98G to MIT, and supporting the overall experimental programme through grants NNX16AC96G and NNX16AC97G to SIO. Observations at Cape Grim are supported largely by the Australian Bureau of Meteorology, CSIRO, the Australian Department of the Environment and Energy (DoEE) and Refrigerant Reclaim Australia (RRA). Mace Head, Ireland, is supported by the Department for Business, Energy & Industrial Strategy (BEIS, UK, formerly the Department of Energy and Climate Change (DECC)) contract 1028/06/2015 to the University of Bristol and the UK Meteorological Office. Ragged Point, Barbados is supported by the National Oceanic and Atmospheric Administration (NOAA, USA), contract RA-133-R15-CN-0008 to the University of Bristol. M.R., L.M.W., M.F.L. and R.L.T. were supported by Natural Environment Research Council grants NE/I021365/1, NE/I027282/1, NE/M014851/1, NE/L013088/1 and NE/N016548/1. A.L.G. is supported by NERC Independent Research Fellowship NE/L010992/1. S.P., T.L., S.L., M.-K.P. and K.-R.K. were supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (no. NRF-2016R1A2B2010663). Observations at Hateruma were partly supported by the Ministry of the Environment of Japan. S.A.M., B.D.H. and G.S.D. are indebted to C. Siso, D. Mondeel, J. D. Nance, F. Moore, J.W. Elkins, B. Vasel, C. Schultz, R. Schnell and J. H. Butler for discussions and assistance with the NOAA measurements considered here, which were made possible in part with support from the NOAA Climate Program Office’s AC4 program.

Reviewer information

Nature thanks Andreas Stohl, Guus Velders and the other anonymous reviewer(s) for their contribution to the peer review of this work.