Supporting the Montreal Protocol: monitoring long-lived halogenated species with atmospheric nadir sounders

氯氟烃（CFCs）最初是在20世纪30年代开发的，作为安全，可靠和无毒的家用制冷剂。这种爆炸性的使用导致了它们在大气中丰度的稳步增加。然而，虽然它们在对流层中是惰性的，但正是这种稳定性使它们能够到达平流层，在那里，紫外线辐射分解释放出氯原子，催化平流层臭氧层的破坏，保护我们免受有害的紫外线辐射，平流层臭氧水平要恢复到1980年前的水平还需要很多年，因为这些物种及其替代物，其中大多数受《蒙特利尔议定书》管制，通常在大气中存在很长时间。继续监测这些物种对于确保丰度按预期下降至关重要。例如，大气监测能够量化中国东部最近非法排放的CFC-11 [Rigby等人，2019].近几十年来，从轨道监测这些也是非常强烈的温室气体的物质一直是红外线临边探测器的领域。目前定期测量这些物种的唯一主动肢体探测器是ACE-FTS（大气化学实验-傅里叶变换光谱仪），自2004年以来一直在运行[Bernath，2017]。随着临边探测的黄金时代即将结束，高光谱红外探测器能否填补卫星监测的空白成为一个问题，一些低辐射噪声、高光谱分辨率的大气最低点探测器测量大气顶部的热红外辐射，包括IASI（红外大气探测干涉仪）和CrIS（跨轨红外探测器）。根据这些仪器记录的大气光谱，我们可以确定一系列痕量气体的浓度，如甲烷、水和二氧化碳。这些仪器有可能提供卤化物质的监测，早期的工作已经显示出使用IASI监测八种此类物质的前景[De隆盖维尔等人，2021年]。使用CrIS的优点是它具有上级信噪比，从而提供了更强有力的趋势和监测IASI无法观察到的其他物种的前景。

Chlorofluorocarbons (CFCs) were first developed in the 1930s as safe, reliable, and non-toxic refrigerants for domestic use. This explosion in use led to a steady increase in their atmospheric abundances. However, while inert in the troposphere, it was this stability which enabled them to reach the stratosphere, where dissociation by ultraviolet (UV) radiation released chlorine atoms catalysing the destruction of the stratospheric ozone layer which protects us from harmful UV radiation.It will be many years before stratospheric ozone levels return to pre-1980 levels because these species and their replacements, the majority of which are regulated by the Montreal Protocol, are generally very long-lived in the atmosphere. Continued monitoring of these species is crucial to ensure abundances are decreasing as expected. For example, atmospheric monitoring was able to quantify recent illegal emissions of CFC-11 from eastern China [Rigby et al., 2019].Over recent decades, monitoring these species, which are also very strong greenhouse gases, from orbit has been the domain of infrared (IR) limb sounders. The only active limb sounder now measuring these species regularly is the ACE-FTS (Atmospheric Chemistry Experiment - Fourier Transform Spectrometer) which has been operating since 2004 [Bernath, 2017]. With the golden age of limb sounding coming to an end, one question is whether hyperspectral nadir IR sounders can fill the satellite monitoring gap.A number of atmospheric nadir sounders, with low radiometric noise and high spectral resolution, measure top-of-atmosphere radiances in the thermal IR; these include IASI (Infrared Atmospheric Sounding Interferometer) and CrIS (Cross-track Infrared Sounder). From the atmospheric spectra recorded by these instruments we can determine the concentrations of a range of trace gases, such as methane, water, and carbon dioxide. These instruments have the potential to provide monitoring of halogenated species, and early work has shown the promise of using IASI for monitoring eight such species [De Longueville et al., 2021]. The advantage of using CrIS is that it possesses superior signal-to-noise, thus providing the prospect of more robust trends and the monitoring of additional species that IASI cannot observe.