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Abstract:
This work intends to contribute to a better understanding of atmospheric ice formation by providing chemical analyses on the composition of ice nucleating particles (INPs) and the residuals contained in ice particles (IPRs). In the temperature range from 0°C to -38°C, INPs are the prerequisite for ice particle formation, and only a small fraction of aerosol particles function as INPs. To find out which aerosol particles these are, INPs and IPRs were analyzed for their chemical components using the single particle mass spectrometer ALABAMA. For this purpose, ground-based aerosol and cloud measurements were carried out at the high altitude research station Jungfraujoch (JFJ). From the analyses, increased correlations with the INP number concentration were found in particular for ions containing sodium, calcium, silicon, chlorine and carbon. These potentially INP-relevant substances were attributed to mineral dust, sea salt particles, and elemental carbon (EC), thus potentially influencing ice particle formation at the JFJ. Particle transport simulations were used to locate the mineral dust and EC type sources in Africa. The analysis of the IPRs revealed that mineral dust and sea salt particles also dominated the composition of the IPR population at JFJ, which is consistent with the conclusions from the INP analyses. Another finding from the IPR analyses arises from the evidence of secondary ice formation, with the sea salt type phasically dominating the IPR population during such cloud periods. In addition, because the ALABAMA did not originally achieve the high measurement efficiency needed for INP measurements, the instrument design was modified as part of this work. With the development of a new aerodynamic lens system (ALS), the implementation of a delayed ion extraction (DIE), and an additional electric shielding (ES), the detection efficiency, the detectable particle size range, and the hit rate of the ALABAMA were significantly improved. The new ALS extends the detectable particle size range, especially in the supermicrometer range (50 %: 230 nm - 3240 nm). By using the DIE and the ES, the hit rate for charged small particles could be significantly improved. In addition, the DIE leads to an increased ion yield of the ion extraction process, which in turn results in a larger effective width of the ablation laser beam and thus hit rates of nearly 100 % are achievable for PSL particles in the size range from 350 nm to 2000 nm.
