Measurements of ozone-depleting substances at the Cape Verde Observatory
Halocarbons – a group of chemicals used widely as refrigerants, foam blowing agents, solvents, and propellants – have had a major influence on the stratospheric ozone layer and climate since the mid-20th century. Since the signing of the Montreal Protocol in 1987, growth rates of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) have declined substantially due to regulation. There remain however substantial scientific challenges that must be addressed to ensure the continued success of the Montreal Protocol. In 2018, emissions of the major ozone depleting substance, CFC-11, were found to have increased despite its global production ban (Montzka et al., 2018). Around half of the new global emissions originated from eastern China and subsequent enforcement action taken in China has avoided a potentially substantial delay in ozone layer recovery and additional climate warming. However, the origin of the remaining half of the new emissions is still unknown due to the sparse observation network. Furthermore, it is not known whether illegal production has occurred for many other ozone depleting substances, some of which are emerging in the atmosphere. An additional challenge is presented by the rapid growth in unregulated anthropogenic emissions of very short-lived substances (VSLS) such as dichloromethane (CH2Cl2) and chloroform (CHCl3). The very uncertain contribution of natural oceanic sources to these VSLS hampers efforts to establish their anthropogenic emission distributions and trends. Even relatively small oceanic emissions of these compounds have the potential to contribute to the lower stratospheric ozone if emissions occur in the tropics.
This project will expand our atmospheric halocarbon automated measurements at the Cape Verde Observatory (CVO) and potentially at the Hateruma (HAT) station in Japan to include a wider range of established and emerging ozone depleting substances. You will also collect new air and seawater VSLS chlorine measurements at Cape Verde to investigate and parametrise in situ ocean production. Thus, you will determine patterns and trends in emerging anthropogenic ozone depleting substances and better constrain natural emissions of short-lived ozone depleting compounds not controlled under the Montreal Protocol.
The current GC-MS system at the CVO, operating since 2014, has very recently been upgraded to trap gases at a much lower temperature than the previous system, enabling the measurement of more volatile halocarbons (CFCs, HCFCs, HFCs). In this project, you will:
-test and harmonise GC column combinations with those used by other groups to allow comparison of relative retention times for new halocarbon species,
-establish calibration scales for compounds not previously measured at the CVO via an intercomparison programme,
-routinely analyse the continuous atmospheric halocarbon data from the CVO and HAT stations,
-establish a program of monthly seawater sampling upwind of the CVO for measurements of CH2Cl2, CHCl3 and other, predominantly natural, VSLS by purge and trap GC-MS, and calculate their oceanic “saturation anomalies”,
-analyses these saturation anomalies for patterns and trends to allow scale-up of these emissions to the tropical ocean.
Why this project?
The project is well aligned with the Department’s vision to conduct interdisciplinary research targeting societally important advances. The project is within one of the Department’s key areas of strength, of atmospheric chemistry and biogeochemical cycling. It will bring innovation to advance the science of halocarbon measurement and emission quantification and will bring new insight into this complex field. Results from this work will be fed into the WMO/UNEP Stratospheric Ozone Assessment (2026), which provides the research community with an up-to-date scientific assessment of ozone depleting substances and their impact on stratospheric ozone.