Laser induced fluorescence instrument for the detection of trace levels of atmospheric sulfur dioxide (SO2)

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.

The impact of this award will be primarily related to pollution reduction and public health, specifically supporting delivery of the 2019 Government Clean Air Strategy. Air pollution is a serious health issue in the UK, linked to an estimated 2.5 - 8 % of deaths, and costs the UK economy around £16 billion per annum (Defra Air Quality Expert Group). Despite significant reductions in the emissions of particulate matter precursors, ambient PM levels in the UK are regulartly above World Health Organization guidelines. Whilst new challenging objectives around reducing the UK population exposure to fine particulate matter (PM2.5) have been set, the best pathway to reach this is not yet clear. Ambient measurements suggest that ammonium sulphate, of which SO2 is a key precursor, remains a major component of urban PM2.5, yet background SO2 levels cannot currently be measured. The instrument obtained through this capital investment will directly support studies to evaluate the effectiveness of further SO2 emission reductions, how they might be best achieved and which sources (energy, fuels, biomass, industry etc.) contribute most to the remaining emissions.
SO2 is also known to be an important ingredient for PM formation in clean background environments and is directly linked to major uncertainties in the radiative forcing of PM in current climate models (Intergovernmental Panel on Climate Change Assessment Report 5). PM formed from SO2 also acts as cloud condensation nuclei, and therefore indirectly impacts radiative forcing through a role in determining cloud droplet number and cloud brightness. The instrument is particularly urgent now since there are major international regulatory changes underway associated with sulfur emissions from maritime shipping that could potentially be quantified directly, allowing the investment to support not only UK policy needs but those at an international level.
The majority of outputs from this asset will be in the form of data and scientific publications. These data will be used to evaluate emissions inventories, and advance our understanding of atmospheric processes important to both air pollution and climate. This in turn will improve our predictive capability of these important issues through active collaborations with the atmospheric chemistry modelling community (e.g. Prof Mathew Evans at the University of York and Prof Mathew Heal at the University of Edinburgh). The atmospheric chemistry group at the University of York has an excellent track record of working with government and international bodies to ensure impact from basic research. The group hosts staff on joint long-term appointments with DEFRA, allowing the science generated from this new asset to feed directly to the Air Quality Expert Group and Government policy.
Equipping the UK community with this novel measurement technology, the first outside of the US and second globally, will establish the UK as a world leader in both the technology and the science it enables. In addition to the current and potential UK collaborations described in Academic Beneficiaries, this asset will also enable new international collaborations with partners keen to use the technology. For example the PI has already been in discussion with the German Aerospace Centre (DLR) about future projects that would involve the asset being installed on the DLR Falcon aircraft measurement platform.
Ultimately this investment will: addresses a key measurement need for the UK atmospheric community; enable fundamental new science that will directly influence UK and global environmental policy; and enhance the UKs position as a leader in the field of atmospheric measurements.