Climate and Air Quality Impact of Airborne Halogens

溴、氯和碘(卤素)是在地球大气中起基本作用的化学元素，与一系列环境问题有关。自20世纪70年代以来，科学家们就已经知道，卤素(主要是氯)破坏了地球平流层(位于地表以上11至50公里)的臭氧层，并导致了臭名昭著的南极臭氧空洞，这是在20世纪80年代首次观察到的。由于臭氧保护地球表面免受有害的太阳辐射，许多卤素化合物的生产是国际法禁止的。然而，现在越来越多的人认识到，卤素对地球大气层的最低层(对流层)也有很大的影响，对气候和空气质量都很重要。直到最近，现场测量才发现，卤素实际上在整个对流层中无处不在，尽管关于它们的来源存在很大争议。与平流层不同，我们认为大多数对流层卤素来自生物圈(例如海洋)和其他自然来源(例如海冰、火山)，尽管这些来源的特征很差。此外，与快速增长的水产养殖部门(例如商业海藻养殖场)和其他行业有关的人类活动正在增加进入对流层的卤素的数量。为什么这很重要？卤素可以做很多事情，但从根本上说，它们改变了对流层的“氧化能力”，也就是说，它的“自我净化”能力和清除各种化合物的能力。从气候的角度来看，这具有重要的影响；这意味着卤素可能(I)改变温室气体(如甲烷)在大气中停留的时间长度，从而影响其全球变暖潜力；(Ii)改变气溶胶(悬浮在大气中的微小颗粒)的产生速度，从而改变云的性质并使地球气候降温。更重要的是，卤素会促进表面臭氧的形成，从而降低空气质量。在地面上，臭氧是一种污染物(和温室气体)，长期暴露在空气中会导致呼吸道疾病，包括哮喘，并对农作物造成损害。在美国沿海和内陆地区，大量检测到含有卤素的氯化物，这是空气质量不良事件的前兆。德国最近也检测到这种化合物水平升高，尽管还没有一项研究全面研究卤素在欧洲空气污染中的作用。作为一个靠近大量海盐(一个主要的卤素来源)的岛国，英国的空气质量可能特别容易受到卤素的影响。最终，尽管卤素具有影响气候和空气质量的杠杆作用，但它们尚未被用于研究和预测这些现象的大多数计算机模型模拟所考虑。我将开发第一个完全集成的生物圈-卤素-气候系统的计算机模型，该模型可以(I)表征和量化对流层卤素来源，(Ii)确定这些气体的大气命运，以及(Iii)在区域到全球尺度上量化它们的影响。一个需要解决的关键问题是：在对流层，卤素的水平、过程和影响随着时间的推移是如何变化的？这一整体建模方法将提供答案，它考虑了由于不断变化的环境因素(例如，海表面温度和海冰覆盖)而引起的生物圈卤素排放的变化。至关重要的是，这将使气候引起的卤素排放反馈能够首次得到评估，这可能会减少或放大未来的气候变化，从而导致更逼真的气候模拟。这项研究提供了强大的新见解，以了解对气候变化和空气质量都很重要的鲜为人知的基本过程，这些过程是当今紧迫的环境问题。

Bromine, chlorine & iodine (halogens) are chemical elements which play a fundamental role in Earth's atmosphere and are implicated in a range of environmental issues. Since the 1970s, scientists have known that halogens (mostly chlorine) damage the ozone layer in Earth's stratosphere (located between 11 & 50 km above the surface) and are responsible for the infamous Antarctic 'Ozone Hole', first observed in the 1980s. As ozone shields Earth's surface from harmful solar radiation, production of many halogen compounds is prohibited under international law. However, it is now increasingly recognised that halogens also exert a large influence on the lowest region of Earth's atmosphere (the troposphere) in ways important for both climate and air quality. Only recently have field measurements revealed that halogens are virtually ubiquitous throughout the troposphere, though there is much debate as to their source. Unlike the stratosphere, we think most tropospheric halogens come from the biosphere (e.g. the ocean) and other natural sources (e.g. sea-ice, volcanoes), though these sources are poorly characterised. In addition, human activities related to the rapidly growing aquaculture sector (e.g. commercial seaweed farms) and other industries are increasing the amount of halogens entering the troposphere.Why is this important? Halogens do a number of things, but fundamentally they alter the troposphere's "oxidising power"; that is, its ability to "self-cleanse" and rid itself of various chemical compounds. From a climate perspective, this has important implications; it means halogens may (i) alter the length of time greenhouse gases, such as methane, remain in the atmosphere and thus influence their global warming potential and (ii) alter the production rate of aerosol (microscopic particles suspended in the atmosphere) which alter cloud properties and cool Earth's climate. What's more, halogens degrade air quality by promoting surface ozone formation. At ground-level, ozone is a pollutant (& greenhouse gas) and prolonged exposure can lead to respiratory ailments, including asthma, and is damaging to crops. Nitryl chloride, a halogen-containing precursor to adverse air quality events, has been detected in large quantities in coastal and inland regions of the USA. Elevated levels of this compound have also recently been detected in Germany, though no study has comprehensively examined the role of halogens in air pollution over Europe. As an island nation in the vicinity to significant quantities of sea salt (a major halogen source), UK air quality could be particularly susceptible to being compromised by halogens. Ultimately, despite the leverage halogens possess to impact both climate & air quality, they have yet to be considered in most computer model simulations used to study and forecast these phenomena. This Fellowship addresses that omission, seeking to unravel the wider impact that airborne halogens have on our environment.I will develop the first fully integrated computer model of the biosphere-halogen-climate system which can (i) characterise and quantify tropospheric halogen sources, (ii) determine the atmospheric fate of these gases and (iii) quantify their impacts, on regional to global scales. A key question to tackle is; in the troposphere, how have halogen levels, processes and impacts changed over time? This holistic modelling approach, which accounts for changes to halogen emissions from the biosphere due to evolving environmental factors (e.g. sea surface temperature & sea-ice cover), will provide the answer. Critically, this will enable climate-induced feedbacks on halogen emissions, which could diminish or amplify future climate change, to be assessed for the first time, leading to climate simulations of greater fidelity. This research provides powerful new insight into poorly understood, yet fundamental processes important for both climate change and air quality - pressing environmental concerns of today.