Understanding the impact of trace level sulphur dioxide on air pollution and climate

颗粒物（PM）是一个主要的空气质量挑战，据估计，仅在英国，每年就有超过29，000人死亡，并且也是当前气候模型预测的一个主要不确定性。根据2018年清洁空气战略，英国目前的目标是到2025年将暴露于小于2.5微米（PM2.5）浓度高于10微克m-3的PM的人数减半。这将是一个挑战，因为PM2.5的主要成分已经通过排放控制减少，这意味着通过大气化学反应产生的二次PM现在占主导地位。因此，如果我们要制定有效的政策来解决PM空气污染和气候问题，了解二次PM的产生是至关重要的。气相二氧化硫（SO2）的氧化是二次无机PM产生的核心。近年来，发达国家二氧化硫排放量的大幅减少导致二氧化硫的背景浓度急剧下降。虽然这是一项重大的政策成功，但即使在非常低的浓度下，SO2仍被认为在PM产生中发挥重要作用，但目前的模型对进一步减少SO2排放的影响存在分歧。提高我们对低SO2浓度下发生的化学反应的理解的最好方法是直接测量它。不幸的是，目前测量SO2的方法不再足够灵敏，无法测量低背景水平，从而破坏了更好地了解二次PM产生的工作。最近，约克大学开发了一种新仪器，用于灵敏地检测痕量二氧化硫。这个博士项目将是第一个使用这种仪器进行急需的观测，能够提高我们对背景SO2化学的理解。这将通过以下目标实现：-使用实验室和现场实验表征新的SO2仪器性能-部署仪器作为3个现场项目的一部分，两个在英国，一个在北极研究巡航-使用这些现场项目的数据，通过与模型预测的比较，挑战和提高我们对大气SO2化学的理解这项工作将解决我们对大气化学理解的重要知识差距，从而直接提高我们设计有效环境政策的能力。

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 predictionsThis work will address an important knowledge gap in our understanding of atmospheric chemistry and thus directly improve our ability to design effective environmental policies.