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

研究气候变化需要长期观察。被动遥感已经成为研究60千米高空大气成分的有力工具。这种观测可以从微波光谱区到红外光谱区，再到紫外/可见光谱区。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。近三十年来，人们一直使用红外光谱仪进行红外观测。瑞士少女峰（Jungfraujoch）的高高山观测点于1984年开始定期进行红外光谱观测。然而，在1950/1951年地球物理学年，使用光栅光谱仪研究地球和太阳大气的开创性观测已经被记录下来。相应的1950/1951年光谱可在约80卷纸上获得，共覆盖2.8 - 23.7微米的光谱范围（对应于422 - 3571 cm-1）。更多的1976-1989年期间的光栅光谱以电子文件的形式存在，但它们只覆盖了狭窄的光谱范围，包括HCl， HF, N2O， CH4特征。由于该仪器的工作方式与目前的FTIR光谱仪相同，从地面朝向太阳，在红外光谱区域进行测量，因此光谱也包含了痕量气体的大气吸收特征，与目前的FTIR光谱相同。我们项目的目的是对1950年和1951年记录的历史光谱进行数字化、保存和分析，同时对1976年至1989年期间的大气成分光谱进行分析。这使我们能够在人类开始显著改变大气成分之前，在其背景水平上研究一些物种的大气成分，并研究它们直到现在的长期演变。我们建议对几个物种的历史光谱进行分析。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，新的检索也是极其重要的。(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)由于快速计算机的可用性和检索代码的改进，检索过程得到了进一步的显著发展。需要回收的微量气体包括CH4、N2O、CO、HCN、HNO3、C2H6、OCS和HCl。对于一些微量气体，如HCl，由于历史光谱的信噪比小，光谱分辨率较低，检索可能会很困难。但是对于这些微量气体，在研究大气成分的长期变化时，给出一个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.