In response to environmental challenges such as acid rain and air pollution, UK emissions of sulfur dioxide (SO2) have been reduced by over 90% since the 1970s. This trend has been replicated across much of the developed world, where SO2 concentrations are now well below the levels where they pose a direct health risk, and this is celebrated as an environmental success story. Background SO2 concentrations (rural, oceanic, etc.) are now below the detection limit of current commercial instrumentation, meaning the UK can no longer accurately quantify ambient SO2 concentrations or evaluate emissions inventories.
However, even at low background levels, SO2 continues plays a major role in the formation of particulate matter (PM), which poses a significant public health risk in the UK and globally. The development of solutions further reduce PM is hindered by the current lack of sensitive SO2 measurements, as this undermines our ability to accurately represent key sulfur chemistry in models used to inform policy on air pollution and climate. This capital investment will provide the UK atmospheric science community with a new, state-of-the-art instrument for the detection of SO2. Sensitive measurements for SO2 have been feasible over the last decade via chemical ionisation mass spectrometry (CIMS), but this is an impractical method that is rarely used due to its high cost and bulky, complicated operation. Recently a more simple optical method that takes advantage of telecommunications industry laser technology has been developed. In addition to being more sensitive than CIMS, it is less expensive to build and maintain, uses robust technology with high longevity, is easier to operate, and is more portable. This compact instrument was developed by project partners at the National Oceanic Atmospheric Administration (NOAA) in the USA, who have successfully demonstrated its performance on both ground and aircraft platforms, where it has proved to be robust, reliable and extremely sensitive. As this instrument is not commercially available, this investment will provide funding for the necessary components and for technical training with the developers at NOAA in order to transfer this exciting new technology to the UK. The new capability will be demonstrated alongside existing SO2 instruments at the Plymouth Marine Laboratories Penlee Point observatory as part of the NERC funded ACRUISE project. The focus of ACRUISE is to investigate the impact on regional air quality of global legislation to reduce shipping fuel sulfur content that comes into force in early 2020. As shipping is a major source of SO2 emissions, particularly in coastal regions, this change in legislation is expected to have a significant effect on global SO2 and associated PM concentrations. This projected reduction in emissions means SO2 levels in coastal areas will likely drop even further below the detection limits of currently available instruments, and so this investment will make a time-critical contribution to UK atmospheric science within the first few months of operation. The instrument will then contribute to two other existing projects in 2020 – 2021, addressing important uncertainties in our understanding of both UK air pollution and the climate impacts of Arctic PM. In both these studies, the new instrument will provide vital information that would not be available otherwise, contributing directly to UK and global environmental policy development. In addition to the above studies, this instrument will be made available to the UK atmospheric science research community and also form the basis of future science proposals. In particular it will enable a targeted study to address the large uncertainties in sulfur’s role in controlling particulate air pollution in the UK, and thus help the UK find effective solutions to achieve its ambitions for PM reduction set out in the 2019 Clean Air Strategy.