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年代以来被认为是平流层臭氧层消耗的主要驱动因素。虽然卤素对平流层的影响已被充分了解，但现在越来越多的人认识到，卤素发挥着更广泛的作用，可能对对流层（地球大气的最低区域）的化学成分产生深远但被忽视的影响[1,2]。首先，卤素改变了对流层的氧化能力（或“自净”能力），从而改变了对流层自身清除污染物的能力[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（如甲烷）在大气中停留的时间，从而影响其变暖潜势，以及（ii）改变气溶胶（悬浮在大气中的微观颗粒）的产生，从而影响云并使气候降温。因此，对流层的生成物具有间接影响气候的杠杆作用，尽管由于大多数气候模式尚未考虑到这些影响，因此对这些影响的限制很差。与英国气象局和利兹大学的科学家合作，该学生将开发并应用最先进的地球系统模型来量化卤素对地球对流层组成的影响。由于对对流层卤素的了解很少（例如，对天然卤素来源如何随时间变化知之甚少），因此在这一迅速发展的领域进行高影响研究的潜力很大。该项目将解决以下关键研究问题：对流层中活性卤素的丰度/分布是什么？在人类世期间，这种丰度/分布是如何变化的？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？对气候相关气体（如甲烷、挥发性有机化合物、对流层臭氧）和气溶胶有何影响？对流层卤素是否影响对工业化前到现在和未来气候强迫的估计？

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?