Opportunity Understanding the indirect climate impacts of halogens in the troposphere

卤素(即氯、溴和碘)气体在地球大气中无处不在，自20世纪70年代以来一直被认为是平流层臭氧层耗尽的主要驱动因素。虽然人们很好地了解了平流层中卤素的影响，但现在越来越多的人认识到，卤素发挥着更广泛的作用，可能会对对流层的化学成分产生深远但被忽视的影响，对流层是地球大气中最低的区域[1，2]。最重要的是，卤素改变了对流层的氧化能力(或“自净”能力)，因此它能够清除污染物[3-5]。从气候角度来看，这具有重要意义，因为卤素可能(I)改变温室气体(例如甲烷)在大气中的停留时间，从而影响其升温潜力，以及(Ii)改变气溶胶(悬浮在大气中的微小颗粒)的产生，从而影响云和冷却气候。因此，对流层卤素拥有间接影响气候的杠杆作用，尽管这些影响受到的限制很少，因为大多数气候模型还没有考虑到它们。这个学生将与英国气象局和利兹大学的科学家合作，开发并应用一种最先进的地球系统模型，以量化卤素对地球高层大气组成的影响。由于对对流层卤素的了解很差(例如，对自然卤素资源如何随时间变化知之甚少)，在这一快速演变的领域开展高影响研究的潜力很大。该项目将解决以下关键研究问题：对流层活性卤素的丰度/分布是什么，以及在人类世期间这种丰度/分布发生了怎样的变化？它们的主要自然/人为来源是什么？卤素如何影响对流层的区域/全球氧化能力？对与气候有关的气体(例如甲烷、挥发性有机化合物、对流层臭氧)和气溶胶有什么影响？对流层卤素是否影响对工业化前到现在和未来气候辐射强迫的估计？

Halogen (i.e. chlorine, bromine & iodine) gases are ubiquitous in Earth's atmosphere and since the 1970sare recognised as the principal driver of stratospheric ozone layer depletion. While the impact of halogensin the stratosphere is well understood, it is now increasingly recognised that halogens play a far wider roleand may have profound, but overlooked, impacts on the chemical composition of the troposphere - thelowest region of Earth's atmosphere[1,2]. At the forefront, halogens alter the troposphere's oxidising power(or "self-cleansing" capacity) and therefore its ability rid itself of pollutants[3-5]. From a climate perspective,this has important implications as halogens may (i) alter the time greenhouse gases (e.g. methane) remainin the atmosphere, thereby influencing their warming potential, and (ii) modify the production of aerosol(microscopic particles suspended in the atmosphere) which effect clouds and cool the climate. Tropospherichalogens thus possess leverage to influence climate indirectly, though these effects are poorly constrainedas most climate models have yet to consider them.Working with scientists at the Met Office and University of Leeds, the student will develop and apply a state-of-the-art Earth System Model to quantify the impacts of halogens on the composition of Earth'stroposphere. As understanding of tropospheric halogens is poor (e.g. little is known of how natural halogensources have changed over time) there is strong potential for high impact research in this rapidly evolvingfield. The project will tackle the following key research questions: What is the tropospheric abundance/distribution of reactive halogens and how has this changedduring the Anthropocene? What are their key natural/anthropogenic sources?How do halogens affect the troposphere's regional/global oxidising power and what are theimplications for climate-relevant gases (e.g. methane, volatile organic compounds, troposphericozone) and aerosol?Do tropospheric halogens affect estimates of pre-industrial to present-day and future climateradiative forcing?