Improving our understanding of the atmospheric sulfur cycle and its impact on air pollution and climate

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Particulate matter (PM) is a major air quality challenge, estimated to be responsible for >29,000 equivalent deaths a year in the UK alone, and also represents a major uncertainty in current climate model predictions due to both the direct and indirect effects on the earths radiative budget. The oxidation of gas phase sulfur dioxide (SO2) is central to the production of PM, and as such the sulfur cycle plays a key role in the climate system. It is understood that anthropogenic sulfur emissions currently offset a significant fraction of the heating from greenhouse gases, but are declining rapidly through emission controls (e.g., regulation of shipping and phasing out of coal). As these anthropogenic emissions decline natural sources of sulfur, in particular biologically derived sulfur compounds emitted from the world's oceans, will increase in their fractional contribution. However, recent work has shown that we have an incomplete understanding of the sulfur cycle, particularly in remote environments, impacting our ability to predict future climate and air pollution scenarios. Until recently, a major challenge has been that the instrumentation available to measure SO2 has not been sensitive enough to detect the low background levels in remote locations, undermining work to better understand the sulfur cycle in these environments. Over the last 3 years a new instrument has been developed at the University of York for the highly sensitive detection of trace levels of SO2, opening up exciting opportunities to increase our understanding of this key atmospheric gas.This project will use newly developed instrumentation to make measurements that will be used to advance our understanding of the natural sulfur cycle. This will be achieved through the following objectives:- Modify the York SO2 instrument for the measurement of SO2 deposition fluxes- Deploy the instrument as part of several field projects, both on the ground and aboard the UK FAAM research aircraft- Use the data from these field projects to challenge and improve our understanding of atmospheric SO2 chemistry through comparison with model predictionsThis work will address important knowledge gaps in our understanding of atmospheric chemistry and thus directly improve our ability to design effective environmental policies.