A refined method for calculating equivalent effective stratospheric chlorine
A refined method for calculating equivalent effective stratospheric chlorine
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DOI：
10.5194/acp-18-601-2018
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发表时间：
2018-01-19
影响因子：
6.3
通讯作者：
Joeckel, Patrick
中科院分区：
文献类型：
--
作者：
Engel, Andreas;Boenisch, Harald;Joeckel, Patrick
氯和溴原子会导致平流层臭氧的催化耗尽。因此，含有氯和溴的消耗臭氧层物质的使用和生产受到《蒙特利尔议定书》的管制，以保护臭氧层。等效平流层氯(EESC)被用来描述卤素释放的氯和溴对平流层臭氧的综合影响。在这里，我们重新讨论计算EESC的概念。我们基于消耗臭氧层物质传播到平流层和反应性卤素释放的先进概念，推导出了EESC的改进公式。引入了一种新的渡越时间分布，其中惰性示踪剂的年龄谱与源气体中无机卤素的释放函数加权。这种分布称为“发布时间分布”。结果表明，与现有公式相比，由化学输运模型TOMCAT得到的无机卤素负荷量更符合实际情况。改进后的公式显示了1980年中纬度平流层低层的EESC水平，明显低于之前计算的水平。1980年通常被用作基准，为了在回收卤素和臭氧方面取得重大进展，平等就业机会委员会必须回到这个基准。假设--在其他条件不变的情况下--EESC值必须回到相同的水平才能使臭氧完全恢复，我们表明，用目前计算EESC的方法估计，平流层这一区域所需的时间将比估计的长10年以上。我们还介绍了一系列敏感性研究，以考察分数释放因子和假设中的变化和不确定性对释放时间分布形状的影响。通过EMAC模式的模拟，我们进一步讨论了EESC作为未来大气动力变化下无机卤素负荷演化的指标的价值。我们发现，虽然平流层输送的预期变化导致EESC和恒定平均年龄的模拟无机卤素负荷之间存在显著差异，但EESC是恒定压力水平上模拟无机卤素的合理替代物。
Chlorine and bromine atoms lead to catalytic depletion of ozone in the stratosphere. Therefore the use and production of ozone-depleting substances (ODSs) containing chlorine and bromine is regulated by the Montreal Protocol to protect the ozone layer. Equivalent effective stratospheric chlorine (EESC) has been adopted as an appropriate metric to describe the combined effects of chlorine and bromine released from halocarbons on stratospheric ozone. Here we revisit the concept of calculating EESC. We derive a refined formulation of EESC based on an advanced concept of ODS propagation into the stratosphere and reactive halogen release. A new transit time distribution is introduced in which the age spectrum for an inert tracer is weighted with the release function for inorganic halogen from the source gases. This distribution is termed the "release time distribution". We show that a much better agreement with inorganic halogen loading from the chemistry transport model TOMCAT is achieved compared with using the current formulation. The refined formulation shows EESC levels in the year 1980 for the mid-latitude lower stratosphere, which are significantly lower than previously calculated. The year 1980 is commonly used as a benchmark to which EESC must return in order to reach significant progress towards halogen and ozone recovery. Assuming that - under otherwise unchanged conditions - the EESC value must return to the same level in order for ozone to fully recover, we show that it will take more than 10 years longer than estimated in this region of the stratosphere with the current method for calculation of EESC. We also present a range of sensitivity studies to investigate the effect of changes and uncertainties in the fractional release factors and in the assumptions on the shape of the release time distributions. We further discuss the value of EESC as a proxy for future evolution of inorganic halogen loading under changing atmospheric dynamics using simulations from the EMAC model. We show that while the expected changes in stratospheric transport lead to significant differences between EESC and modelled inorganic halogen loading at constant mean age, EESC is a reasonable proxy for modelled inorganic halogen on a constant pressure level.