Digitization and use of historical spectra from 1950/51 for the retrieval of various trace gases from the Jungfraujoch site (46.55N, 7.98E, 3580m)

The Sphinx Observatory at Jungfraujoch (46.55N, 7.98E, 3580m) has been pivotal in atmospheric research, particularly atmospheric sounding, since its inception. This study revisits the observatory's pioneering work in the 1950s when a Pfund-type, dispersive spectrometer was utilized to capture infrared solar spectra, initially recorded on paper rolls. While the initial focus was on solar spectrum analysis, these historical spectra now offer a unique window into the atmospheric composition of the 1950s. The solar absorption spectroscopy at Jungfraujoch allows the retrieval of the atmospheric composition. Our research is twofold. First, we developed a specialized software for digitizing and calibrating these historical spectra, and making the spectra available for the scientific community. Second, using these digitized spectra, we determined the atmospheric concentrations of carbon monoxide (CO) and dichlorodifluoromethane (CFC12) from that era, comparing our findings with current model projections. The results show an intriguing disparity. For CO, the observed concentrations in 1950/51 were lower than those predicted by models. As expected, CFC12 levels were significantly lower than current levels, averaging at 0.75E15 molecules per square centimeter. This predates James Lovelock's first detection of CFCs in the 1970s and suggests a minor but detectable presence of CFC12 in the 1950s atmosphere. Ongoing efforts focus on extending this analysis to other trace gases, aiming to enrich our understanding of the atmospheric composition in 1950/51.