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. Current UK targets, as outlined in the 2018 Clean Air Strategy, are to halve the number of people exposed to PM smaller than 2.5 um (PM2.5) concentrations above 10 ug m-3 by 2025. This is going to be a challenge as primary components of PM2.5 have been reduced through emissions controls, meaning secondary PM, produced through atmospheric chemical reactions, now dominate.
Understanding secondary PM production is therefore vital if we are to develop effective policies to tackle both PM air pollution and climate. The oxidation of gas phase sulphur dioxide (SO2) is central to the production of secondary inorganic PM. Significant reductions in SO2 emissions in the developed world over recent years have resulted in background concentrations of SO2 falling drastically. Although this is a major policy success, even at very low concentrations SO2 is still thought to play an important role in PM production, but current models disagree on the impact further SO2 emission reductions will have. The best way to improve our understanding of the chemistry occurring at low SO2 concentrations is to directly measure it. Unfortunately current methods for measuring SO2 are no longer sensitive enough to measure the low background levels, undermining work to better understand the production of secondary PM. Recently a new instrument has been developed at the University of York for the sensitive detection of trace levels of SO2. This PhD project will be the first to use this instrument to make the much needed observations capable of improving our understanding of background SO2 chemistry. This will be achieved through the following objectives:
– Characterise new SO2 instrument performance using lab and field experiments
– Deploy instrument as part of 3 field projects, two in the UK and one aboard a research cruise to the Arctic
– Use the data from these field projects to challenge and improve our understanding of atmospheric SO2 chemistry through comparison with model predictions
This work will address an important knowledge gap in our understanding of atmospheric chemistry and thus directly improve our ability to design effective environmental policies.