Investigating the atmospheric composition from the 1950s on using historical solar absorption infrared spectra

研究气候变化需要长期的观察。被动遥感已成为研究高达约60公里高度的大气组成的有力工具。这种观测可以从微波光谱区域通过红外到UV/Vis进行。红外光谱区的测量具有很高的相关性，因为可以探测到平流层和对流层中的许多微量气体。大约三十年来，人们一直使用FTIR光谱仪进行红外观测。瑞士少夫劳约克的高山遗址于1984年开始定期进行FTIR观测。然而，在地球物理年1950/1951年，已经记录了使用光栅光谱仪进行的开创性观测，以调查地球和太阳大气。1950/1951年的相应光谱可在约80个纸卷上获得，总共覆盖2.8-23.7微米的光谱范围(对应于422-3571厘米-1)。更多的光栅谱以电子文档的形式提供了1976-1989年的时间段，但它们只覆盖了选定的包括HCl、HF、N2O、CH4特征的狭窄光谱范围。由于该仪器的工作方式与目前的FTIR光谱仪相同，从地面朝太阳看，并在红外光谱区测量，因此光谱也包含了痕量气体的大气吸收特征，与当前的FTIR光谱一样。我们项目的目的是数字化、保存和分析1950年和1951年记录的历史光谱，以及对1976-1989年间大气成分的光谱分析。这使得我们能够在人类开始显著改变大气组成之前，研究其背景水平上的少数物种的大气组成，并研究它们直到现在的长期演化。我们建议分析几个物种的历史光谱。即使对于那些已经分析了历史光谱子集的痕量气体，由于两个原因，新的恢复也是极其重要的。(1)由于新的实验室测量和分子光谱学的新发展，光谱数据发生了变化；(2)由于有了快速计算机和检索代码的改进，检索过程得到了进一步的发展。待回收的痕量气体包括CH4、N2O、CO、HCN、HNO3、C2H6、OCS和HCl。对于像HCl这样的少数痕量气体，由于历史光谱的信噪比较小，光谱分辨率较低，可能很难进行反演。但对于这些痕量气体，在研究大气成分的长期变化时，给出上限是有价值的信息。

Studying climate change requires long-term observations. Passive remote sensing has been established as a powerful tool for studying the composition of the atmosphere up to about 60 km altitude. Such observations can be performed from the microwave spectral region through the infrared and into the UV/Vis. Measurements in the infrared spectral region are of high relevance, because many trace gases in the stratosphere and troposphere can be detected. For about three decades infrared observations have been performed using FTIR-spectrometers. The high-alpine site at Jungfraujoch/Switzerland started regular FTIR-observations in 1984. However, pioneering observations using a grating spectrometer were already recorded in the geophysical year 1950/1951 to investigate the Earth’s and solar atmosphere. The corresponding spectra for 1950/1951 are available on ~80 paper rolls, covering altogether the 2.8 – 23.7 micro meter spectral range (corresponding to 422 – 3571 cm-1). More grating spectra are available as electronic files for the 1976-1989 time period, but they cover only narrow spectral ranges selected to include HCl, HF, N2O, CH4 features. Since the instrument works in the same way as current FTIR-spectrometers, looking from the ground towards the sun and measuring in the infrared spectral region, the spectra also contain the atmospheric absorption features of the trace gases, as the current FTIR spectra. The aim of our project is to digitize, conserve, and analyze the historical spectra recorded in 1950 and 1951, together with an analysis of spectra for the 1976-1989 time period with regard to atmospheric composition. This allows allow us to study atmospheric composition, for a few species at their background levels, before mankind began to significantly change it, and study their long-term evolution until the present time. We propose to analyze the historical spectra for several species. Even for those trace gases where a subset of the historical spectra have been analyzed, a new retrieval is extremely important due to two reasons. (i) the spectral data have changed because of new laboratory measurements and new developments in molecular spectroscopy and (ii) the retrieval processes have been further developed significantly due to the availability of fast computers and improvements in the retrieval codes. Trace gases of interest to be retrieved include CH4, N2O, CO, HCN, HNO3, C2H6, OCS and HCl. For a few trace gases, like HCl, the retrieval might be difficult, due to the small signal-to-noise ratio and the lower spectral resolution of the historical spectra. But for these trace gases giving an upper limit is valuable information when studying the long-term change in the atmospheric composition.