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

氯氟烃(CFCs)最早是在20世纪30年代作为安全、可靠和无毒的家用制冷剂开发出来的。这种使用的爆炸性增长导致它们在大气中的丰度稳步增加。然而，尽管对流层中存在惰性，但正是这种稳定性使它们能够到达平流层，在那里，紫外线(UV)辐射的解离释放出氯原子，催化破坏平流层臭氧层，从而保护我们免受有害的紫外线辐射。平流层臭氧水平需要多年才能恢复到1980年前的水平，因为这些物种及其替代品通常在大气中生存很长时间，其中大部分受到《蒙特利尔议定书》的管制。对这些物种的持续监测对于确保物种丰度按预期减少至关重要。例如，大气监测能够量化最近从中国东部非法排放的氟氯化碳-11[Rigby等人，2019年]。近几十年来，从轨道上监测这些物种一直是红外肢体探测仪的领域，这些物种也是非常强烈的温室气体。目前唯一定期测量这些物种的活跃肢体探测仪是自2004年以来一直运行的ACE-FTS(大气化学实验-傅立叶变换光谱仪)[Bernath，2017]。随着肢体探测黄金时代的结束，一个问题是高光谱探测仪能否填补卫星监测的空白。一些低辐射噪声和高光谱分辨率的大气探测仪测量热红外中的大气顶部辐射，其中包括IASI(红外大气探测干涉仪)和CRIS(交叉跟踪红外探测仪)。从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对卤化物种的监测，早期工作显示了利用国际生物多样性倡议监测8种此类物种的前景[De Longueville等人，2021年]。使用CRIS的优点是它具有优越的信噪比，从而提供了更强劲的趋势和对IASI无法观察到的更多物种的监测的前景。

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.