Middle Atmosphere Processes and Lifetime Evaluation for ODSs and GHGs (MAPLE)

排放到大气中的气体可能会持续数年甚至数百年。气体的去除速度由其所谓的寿命决定。因此，要了解例如人类活动排放的污染物气体的影响，就必须对其大气寿命有一个准确的了解。然而，目前许多关键污染物气体的已知寿命存在很大的不确定性。消耗臭氧物质(Ods)，如氯氟烃(CFCs)，是在平流层分解释放氯和溴的长寿源气体。根据《蒙特利尔议定书》，这些物种的排放已被逐步淘汰，预计臭氧层将在未来50-100年内恢复。然而，这种恢复的速度将取决于这些气体及其替代品的大气寿命，这些气体仍在排放。事实上，这些大气寿命目前存在很大的不确定性，用于未来卤素负荷的所有模型预测(通过预测的表面混合比模型边界条件)。例如，在世界气象组织和政府间气候变化专门委员会的评估中，一种主要的氯氟烃CFC-11的大气寿命为45年，尽管其他研究表明其寿命长达60年。最近建立的世界气候研究计划(WCRP)平流层过程及其在气候中的作用(SPARC)项目认识到了这一关键不确定性，该项目使用最先进的3-D化学-气候模型(CCM)中的最新实验室数据重新评估这些消耗臭氧层物质及其替代品(如氢氟碳化合物)的寿命。这些物种也是有效的温室气体(GHGs)，它们已知大气寿命的变化将改变它们将如何影响气候变化的估计(以它们的全球变暖/温度潜力(GWP/GTP)衡量)。该项目将确保英国的化学-气候模型(UKCA)充分参与WCRP/SPARC的重新评估。寿命估计直接影响对未来臭氧恢复的模型预测。以前CCM关于臭氧层恢复的研究使用了基于旧的寿命估计和一个简单的盒子模型的未来地表消耗臭氧层物质浓度预测。因此，未来臭氧变化的主要驱动力，平流层氯和溴的负荷，一直受到粗略的与时间相关的边界条件的约束。通过消除这一限制，使用主要消耗臭氧层物质的排放通量表面边界条件运行CCM，并允许模型本身预测未来十年氯和溴的清除，可以获得更真实的臭氧回收率表示。我们将在这个项目中进行这些模拟。源气体具有很长的寿命(数百到数千年)，太稳定了，不会通过分解影响平流层臭氧，但它们总是强有力的温室气体。对于这些气体，上层大气(中间层)的损失过程通常被忽视或被非常粗暴地对待，可能会大大缩短其大气寿命，从而降低其估计的气候影响。这类气体的三个例子是NF3、CFC-115和SF6。我们已经确定，这些气体与存在于中间层上层的金属原子(Fe、Na和Mg)的反应可能是一个重要的附加汇，并与Lyman-α光解和其他反应竞争。我们将在实验室中评估这些汇的速率。对于所有研究的气体，我们将通过重新计算它们的GWP/GTP值来得出新的、改进的对气候影响的估计。这个项目将使用英国核心对流层-平流层化学-气候模型(UKCA)。所执行的测试和开发工作将为英国研究人员社区带来一个改进的、更彻底测试的模型

Gases emitted into the atmosphere can persist for many years or even centuries. The rate at which a gas is removed is determined by its so-called lifetime. Therefore, to understand the impact of, for example, pollutant gases emitted by human activity, it is essential to have an accurate knowledge of their atmospheric lifetimes. However, there is currently large uncertainty in the known lifetime of many key pollutant gases.Ozone-depleting substances (ODS), such as chlorofluorocarbons (CFCs), are long-lived source gases which decompose in the stratosphere to release chlorine and bromine. Under the Montreal Protocol the emissions of these species have been phased out and the ozone layer is expected to recover over the next 50-100 years. However, the rate of this recovery will depend on the atmospheric lifetime of the these gases and their replacements which are still being emitted. In fact, there is currently significant uncertainty in these atmospheric lifetimes, which are used in all model predictions of future halogen loadings (via predicted surface mixing ratio model boundary conditions). For example, a major chlorofluorocarbon CFC-11 has a quoted atmospheric lifetime of 45 years in WMO and IPCC assessments, although other studies suggest a lifetime of up to 60 years.This key uncertainty has been recognised by the recent establishment of a World Climate Research Program (WCRP) Stratospheric Processes and their Role in Climate (SPARC) project to re-evaluate the lifetimes of these ODS and their replacements (such as hydrofluorocarbons, HFCs) using up-to-date laboratory data in state-of-the-art 3-D chemistry-climate models (CCMs). These species are also efficient greenhouse gases (GHGs) and changes to their known atmospheric lifetime will change estimates of how they will affect climate change (as measured by their global warming/temperature potential (GWP/GTP)). This project will ensure full participation of the UK's chemistry-climate model (UKCA) in the WCRP/SPARC re-evaluation.Lifetime estimates directly affect model predictions of future ozone recovery. Previous CCM studies of the recovery of the ozone layer have used projected future surface ODS concentrations based on old lifetime estimates and a simple box model. Therefore, the major driver of future ozone change, the stratospheric chlorine and bromine loading, has been constrained with crude time-dependent boundary conditions. A more realistic representation of the rate of ozone recovery can be obtained by removing this constraint and running the CCMs with emission flux surface boundary conditions for major ODSs, and allow the model itself to predict the future decadal removal of chlorine and bromine. We will perform these simulations within this project.Source gases with very long lifetimes (many hundreds to thousands of years) are too stable to affect stratospheric ozone by decomposition but they are invariably potent GHGs. For these gases loss processes in the upper atmosphere (mesosphere), which are usually ignored or treated very crudely, could significantly reduce their atmospheric lifetime, thereby decreasing their estimated climate impact. Three examples of such gases are NF3, CFC-115, and SF6. We have identified that the reactions of these gases with metallic atoms (Fe, Na and Mg) which are present in the upper mesosphere could be an important additional sink and compete with Lyman-alpha photolysis and other reactions. We will evaluate the rates of these sinks in the laboratory.For all of the gases studied, we will produce new, improved estimates of their climate impact by recalculating their GWP/GTP values.This project will use the UK's core tropospheric-stratospheric chemistry-climate model (UKCA). The testing and development work performed will lead to an improved, and more thoroughly tested, model for the UK community of researchers