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Why is Lower Stratospheric Ozone Not Recovering?

为什么平流层低层臭氧没有恢复？

基本信息

批准号：
NE/V011863/1
负责人：
Martyn Chipperfield
金额：
$ 82.73万
依托单位：
University of Leeds
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2022
资助国家：
英国
起止时间：
2022 至无数据
项目状态：
未结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FV011863%2F1
关键词：
Why Lower Stratospheric Ozone Recovering

项目摘要

Depletion of stratospheric ozone allows larger doses of harmful solar ultraviolet (UV) radiation to reach the surface leading to increases in skin cancer and cataracts in humans and other impacts, such as crop damage. Ozone also affects the Earth's radiation balance and, in particular, ozone depletion in the lower stratosphere (LS) exerts an important climate forcing. While most long-lived ozone-depleting substances (ODSs, e.g. chlorofluorocarbons, CFCs) are now controlled by the United Nations Montreal Protocol and their abundances are slowly declining, there remains significant uncertainty surrounding the rate of ozone layer recovery. Although signs of recovery have been detected in the upper stratosphere and the Antarctic, this is not the case for the lower stratosphere at middle and low latitudes. In fact, contrary to expectations, ozone in this extrapolar lower stratosphere has continued to decrease (by up to 5% since 1998). The reason(s) for this are not known, but suggested causes include changes in atmospheric dynamics or the increasing abundance of short-lived reactive iodine and chlorine species. We will investigate the causes of this ongoing depletion using comprehensive modelling studies and new targeted observations of the short-lived chlorine substances in the lower stratosphere.While the Montreal Protocol has controlled the production of long-lived ODSs, this is not the case for halogenated very short-lived substances (VSLS, lifetimes <6 months), based on the belief that they would not be abundant or persistent enough to have an impact. Recent observations suggest otherwise, with notable increases in the atmospheric abundance of several gases (CH2Cl2, CHCl3), due largely to growth in emissions from Asia. A major US aircraft campaign based in Japan in summer 2021 will provide important new information on how these emissions of short-lived species reach the stratosphere via the Asian Summer Monsoon (ASM). UEA will supplement the ACCLIP campaign by making targeted surface observations in Taiwan and Malaysia which will help to constrain chlorine emissions.The observations will be combined with detailed and comprehensive 3-D modelling studies at Leeds and Lancaster, who have world-leading expertise and tools for the study of atmospheric chlorine and iodine. The modelling will use an off-line chemical transport model (CTM), ideal for interpreting observations, and a coupled chemistry-climate model (CCM) which is needed to study chemical-dynamical feedbacks and for future projections. Novel observations on how gases are affected by gravitational separation will be used to test the modelled descriptions of variations in atmospheric circulation. The CTM will also be used in an 'inverse' mode to trace back the observations of anthropogenic VSLS to their geographical source regions. The models will be used to quantify the flux of short-lived chlorine and iodine species to the stratosphere and to determine their impact on lower stratospheric ozone trends. The impact of dynamical variability will be quantified using the CTM and the drivers of this determined using the CCM. The model results will be analysed using the same statistical models used to derive the decreasing trend in ozone from observations, including the Dynamical Linear Model (DLM). Overall, the results of the model experiments will be synthesised into an understanding of the ongoing decrease in lower stratospheric ozone. This information will then be used to make improved future projections of how ozone will evolve, which will feed through to the policy-making process (Montreal Protocol) with the collaboration of expert partners. The results of the project will provide important information for future international assessments e.g. WMO/UNEP and IPCC reports.

平流层臭氧的消耗使更大剂量的有害太阳紫外线辐射到达地表，导致人类皮肤癌和白内障的增加以及其他影响，如农作物受损。臭氧还影响到地球的辐射平衡，特别是平流层下部的臭氧消耗产生了重要的气候强迫。虽然大多数寿命较长的消耗臭氧层物质（臭氧消耗物质，如氯氟化碳、氟氯化碳）现在都受到《联合国蒙特利尔议定书》的控制，而且其丰度正在缓慢下降，但臭氧层恢复的速度仍然存在很大的不确定性。虽然在平流层上部和南极已发现复苏迹象，但在中低纬度的平流层下部情况并非如此。事实上，与预期相反，极外平流层下部的臭氧持续减少（自1998年以来减少了5%）。其原因尚不清楚，但建议的原因包括大气动力学的变化或短寿命活性碘和氯物种的增加。我们将通过全面的模拟研究和对平流层下部短寿命氯物质的新的有针对性的观测，调查这种持续消耗的原因。虽然《蒙特利尔议定书》控制了长寿命臭氧消耗物质的生产，但对于寿命非常短的卤化物质，情况并非如此（VSLS，寿命<6个月），基于这样的信念，即它们不会足够丰富或持久，从而产生影响。最近的观测表明情况并非如此，大气中几种气体（CH 2Cl 2、CHCl 3）的丰度显著增加，这主要是由于亚洲排放量的增加。2021年夏天，美国在日本进行的一项大型飞机活动将提供重要的新信息，说明这些短寿命物种的排放如何通过亚洲夏季风（ASM）到达平流层。UEA将通过在台湾和马来西亚进行有针对性的地面观测来补充ACCLIP活动，这将有助于限制氯的排放。这些观测将与利兹和兰开斯特的详细和全面的三维建模研究相结合，这两个城市在大气氯和碘的研究方面拥有世界领先的专业知识和工具。建模将使用离线化学传输模型（CTM），这是解释观测结果的理想选择，以及研究化学动力反馈和未来预测所需的化学-气候耦合模型（CCM）。关于气体如何受到重力分离影响的新观测将用于测试大气环流变化的模拟描述。CTM还将以“反向”模式用于将人为VSLS的观测结果追溯到其地理来源区域。这些模型将用于量化进入平流层的短寿命氯和碘物质的通量，并确定其对平流层下部臭氧趋势的影响。将使用CTM量化动态可变性的影响，并使用CCM确定其驱动因素。将使用用于从观测中得出臭氧减少趋势的相同统计模型，包括动态线性模型，对模型结果进行分析。总体而言，模型实验的结果将被综合用于理解平流层下部臭氧的持续减少。然后，将利用这些信息对臭氧今后的演变情况作出更好的预测，并在专家伙伴的协作下，将这些信息反馈给决策进程（《蒙特利尔议定书》）。该项目的结果将为今后的国际评估，例如气象组织/环境规划署和气候小组的报告提供重要信息。