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》及其修正案对氟氯化碳、长寿命氯化溶剂和哈龙等物质的生产和使用进行了管制，最近在2016年10月的基加利修正案中进行了扩展。调控的成功反映在许多物质的大气混合比的降低上。由于一些物质的逐步淘汰，其替代品（如长寿命氢氟碳化合物）的大气负荷正在增加，导致未来全球变暖。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可检测的水平。拟议项目的重点是在加勒比项目内利用一架客机进行大气测量，对对流层上层和平流层最下层的卤化气体进行新的观测。研究课题包括：(1)UT/LS中的HFOs；(2)对流层上层卤化气体的半球间梯度；(3)南亚夏季风的影响。在飞行高度为10-12公里的情况下，该平台可以评估对流层上层卤化示踪剂的混合比率，作为进入最下层平流层的准等熵输送的入口点。由于大气的平均寿命为几天到几周，新使用的氢氟烃类的寿命足够长，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底层的可能性。在夏季，南亚夏季风为污染物输送到平流层最底层提供了另一条途径，它对大气的化学成分有强烈影响，使污染物从人口稠密地区和发展中经济体中上升，卤化物质的排放增加。报告的卤代烃排放量与根据观测到的大气趋势得出的排放估计值并不总是相符。例如，CCl4的大气混合率下降的速度低于其寿命和报告排放量的预期速度，最近报告的CFC-11也有类似的发现。大多数卤代烃主要由北半球的工业过程排放，造成半球间明显的差异。半球间梯度的变化可能与大气输送或排放收支的变化有关。除了站网提供的数据库之外，机载测量有可能对目前用于推导自上而下排放的模式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箱模型来解决。

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.