Mechanism of ozone loss under enhanced water vapour conditions in the mid-latitude lower stratosphere in summer
Mechanism of ozone loss under enhanced water vapour conditions in the mid-latitude lower stratosphere in summer
复制标题
DOI：
10.5194/acp-19-5805-2019
复制
发表时间：
2018-12
影响因子：
6.3
通讯作者：
Sabine Robrecht;B. Vogel;J. Grooß;K. Rosenlof;T. Thornberry;A. Rollins;M. Krämer;L. Christensen;R. Müller
中科院分区：
文献类型：
--
作者：
Sabine Robrecht;B. Vogel;J. Grooß;K. Rosenlof;T. Thornberry;A. Rollins;M. Krämer;L. Christensen;R. Müller
摘要。水蒸气对流注入到中纬度最低的平流层会影响平流层臭氧。相关的潜在臭氧损失过程需要低温和较高的水蒸气混合比。由于这种臭氧损失是由液体气溶胶上的非均相氯活化引起的，由于火山喷发或地球工程导致的硫酸盐气溶胶表面积的增加可能会增加其发生的可能性。然而，这一臭氧损失过程的化学机制尚未得到足够详细的分析，其对各种条件的敏感性也尚不清楚。在与温室气体增加有关的气候变化条件下，预计平流层冷却和对流注入平流层的水蒸气都会增加。了解低温、水蒸气升高和硫酸盐颗粒增强对这种臭氧损失机制的影响是估计气候变化和潜在硫酸盐地球工程对中纬度臭氧影响的关键步骤。本文详细分析了臭氧损耗机理及其对各种平流层条件的敏感性。通过使用平流层化学拉格朗日模型（CLaMS）进行盒子模型研究，沿着7 d的反向轨迹模拟了化学过程。该轨迹的计算忽略了相邻气团的混合。化学模拟初始化使用区域调查排放与大气成分、云和气候耦合研究（SEAC4RS）飞机活动（2013年，德克萨斯州）期间的测量数据，该活动在100 hPa左右的压力水平下遇到了水汽混合比升高10.6 ppmv的情况。本文详细分析了臭氧损失机理，包括氯活化、氯催化臭氧损失循环、活性氯的维持和活性氮氧化物自由基（NOx）的作用。以197至202k温度范围内的实际轨迹为重点，必须超过并维持10.6 ppmv的水蒸气阈值，才能发生平流层臭氧损失。我们研究了水蒸气阈值对温度、硫酸盐含量、无机氯（Cly）、无机氮（NOy）和无机溴（Bry）的敏感性。水蒸气阈值主要由温度和硫酸盐含量决定。然而，臭氧损失的数量取决于氯气、溴和氯活化可以维持的时间长度。NOy既影响臭氧形成的潜力，也影响产生氯活化和失活的反应之间的平衡，这决定了水蒸气的阈值。我们的研究结果表明，为了消耗臭氧，在低温的水蒸气阈值条件下，必须保持24至36小时的氯活化时间。在北美季风对流层顶标准条件下，采用化学箱模式沿真实轨迹模拟，发现水汽混合比为20 ppmv时臭氧最大损失为9%。对于相同的轨迹，使用观测条件（10.6 ppmv H2O），模拟臭氧损失的发生取决于假设的硫酸盐量。需要对当前和未来的可能性进行详细分析，以评估夏季中纬度平流层下层水汽条件的增强是否会导致显著的臭氧损失。
Abstract. Water vapour convectively injected into the mid-latitude lowermost stratosphere could affect stratospheric ozone. The associated potential ozone loss process requires low temperatures together with elevated water vapour mixing ratios. Since this ozone loss is initiated by heterogeneous chlorine activation on liquid aerosols, an increase in sulfate aerosol surface area due to a volcanic eruption or geoengineering could increase the likelihood of its occurrence. However, the chemical mechanism of this ozone loss process has not yet been analysed in sufficient detail and its sensitivity to various conditions is not yet clear. Under conditions of climate change associated with an increase in greenhouse gases, both a stratospheric cooling and an increase in water vapour convectively injected into the stratosphere are expected. Understanding the influence of low temperatures, elevated water vapour and enhanced sulfate particles on this ozone loss mechanism is a key step in estimating the impact of climate change and potential sulfate geoengineering on mid-latitude ozone. Here, we analyse the ozone loss mechanism and its sensitivity to various stratospheric conditions in detail. By conducting a box-model study with the Chemical Lagrangian Model of the Stratosphere (CLaMS), chemistry was simulated along a 7 d backward trajectory. This trajectory was calculated neglecting mixing of neighbouring air masses. Chemical simulations were initialized using measurements taken during the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) aircraft campaign (2013, Texas), which encountered an elevated water vapour mixing ratio of 10.6 ppmv at a pressure level around 100 hPa. We present a detailed analysis of the ozone loss mechanism, including the chlorine activation, chlorine-catalysed ozone loss cycles, maintenance of activated chlorine and the role of active nitrogen oxide radicals (NOx). Focussing on a realistic trajectory in a temperature range from 197 to 202 K, a threshold in water vapour of 10.6 ppmv has to be exceeded and maintained for stratospheric ozone loss to occur. We investigated the sensitivity of the water vapour threshold to temperature, sulfate content, inorganic chlorine (Cly), inorganic nitrogen (NOy) and inorganic bromine (Bry). The water vapour threshold is mainly determined by the temperature and sulfate content. However, the amount of ozone loss depends on Cly, Bry and the duration of the time period over which chlorine activation can be maintained. NOy affects both the potential of ozone formation and the balance between reactions yielding chlorine activation and deactivation, which determines the water vapour threshold. Our results show that in order to deplete ozone, a chlorine activation time of 24 to 36 h for conditions of the water vapour threshold with low temperatures must be maintained. A maximum ozone loss of 9 % was found for a 20 ppmv water vapour mixing ratio using North American Monsoon (NAM) tropopause standard conditions with a chemical box-model simulation along a realistic trajectory. For the same trajectory, using observed conditions (of 10.6 ppmv H2O), the occurrence of simulated ozone loss was dependent on the sulfate amount assumed. Detailed analysis of current and future possibilities is needed to assess whether enhanced water vapour conditions in the summertime mid-latitude lower stratosphere lead to significant ozone loss.