Airborne Observations of Halogenated Trace Gases in the Upper Troposphere and Lowermost Stratosphere

大气中的氯化和溴化示踪剂对臭氧层有害，许多是具有高辐射效率的气候活性气体。《蒙特利尔议定书》及其修正案对氯氟烃、长效氯化溶剂和哈龙等物质的生产和使用进行了管制，最近一次延长是在2016年10月的《基加利修正案》中。监管的成功体现在降低了许多物质的大气混合比例。由于几种物质的逐步淘汰，它们的替代品，如长寿命氢氟碳化合物(HFC)的大气负荷正在增加，导致未来的全球变暖。现在，新的短寿命HFC(所谓的HFO，氢氟烯烃)正在投入使用，它们在大气中的混合比例已经达到了可检测到的量。拟议项目的重点是在CARIBIC项目范围内利用一架客机进行大气测量，对对流层上层和平流层最低层的卤化气体进行新的观测。将讨论的研究主题是(1)UT/LS中的HFO，(2)对流层上部卤化气体的半球间梯度，以及(3)南亚夏季风的影响。该平台允许评估对流层上部卤化示踪剂的混合比率，作为准等熵输送到最低平流层的入口点。由于大气平均寿命在几天到几周的数量级，新使用的HFO的寿命足够长，可以被输送到对流层上层。对流层顶周围的测量将提供数据，以评估卤素进一步输送到平流层最低层的可能性。夏季，南亚夏季风为污染物向平流层最低层输送提供了另一条途径，并对大气的化学成分产生强烈影响，使来自人口稠密地区和卤化物排放量不断增加的发展中经济体的污染物上升。报告的碳氢化合物排放量和根据观测到的大气趋势得出的排放量估计值并不总是一致的。例如，从其寿命和报告排放量来看，CCl4在大气中的混合比率下降的速度比预期的要慢，最近报告的CFC-11也有类似的结果。大多数卤化碳是工业过程排放的，主要是在北半球，造成明显的半球间差异。半球间梯度的变化可能与大气输送或排放预算的变化有关。除了空间站网络提供的数据库之外，空中测量有可能对目前用于推导自上而下排放的模型框架施加进一步的观测限制。这个问题将使用飞往南半球的航班数据和现有的12箱机型来解决。

Chlorinated and brominated tracers in the atmosphere are harmful to the ozone layer and many are climate active gases with high radiative efficiencies. Production and use of substances such as chlorofluorocarbons, long-lived chlorinated solvents and halons are regulated in the Montreal Protocol and its amendments, most recently extended in the Kigali amendment in October 2016. The success of regulation is reflected in decreasing atmospheric mixing ratios of many substances. As a consequence of the phase-out of several substances, the atmospheric load of their replacements such as long-lived hydrofluorocarbons (HFC) is increasing, resulting in future global warming. Now, new short-lived HFC (so-called HFO, hydrofluoroolefins) are coming into use, with their mixing ratios in the atmosphere already having reached detectable amounts. The proposed project focuses on new observations of halogenated gases in the upper troposphere and lowermost stratosphere within the CARIBIC project employing a passenger aircraft for atmospheric measurements. Research topics to be addressed are (1) HFOs in the UT/LS, (2) interhemispheric gradients of halogenated gases in the upper troposphere and (3) the impact of the South Asian summer monsoon.With a flight altitude of 10-12 km the platform allows to assess mixing ratios of halogenated tracers in the upper troposphere as an entry point for quasi isentropic transport into the lowermost stratosphere. With atmospheric mean lifetimes of the order of days to weeks, the newly used HFOs live sufficiently long to be transported to the upper troposphere. The measurements around the tropopause will provide data to assess the potential of further transport of halogens into the lowermost stratosphere. In summer, the South Asian summer monsoon provides another pathway for the transport of pollutants to the lowermost stratosphere, and it has a strong impact on the chemical composition of the atmosphere uplifting pollutants from densely populated regions and developing economies with increasing emissions of halogenated substances. Reported halocarbon emissions and emission estimates derived from observed trends in the atmosphere do not always match. For example, atmospheric mixing ratios of CCl4 decrease at a slower rate than would be expected from its lifetime and reported emissions, and similar findings were recently reported for CFC-11. Most halocarbons are emitted from industrial processes predominantly in the northern hemisphere resulting in pronounced interhemispheric differences. Variations in the interhemispheric gradient may be related to changes either in atmospheric transport or in emission budgets. Adding to the database provided by station networks, airborne measurements have the potential to put further observational constraint to the current model framework for deriving top-down emissions. This question will be addressed using data from flights into the southern hemisphere and an existing 12-box model.