Chemical composition of atmospheric clusters

New Particle Formation (NPF) in the atmosphere is an emergent research field in environmental sciences. In recent years, the measurement techniques have improved to analyse charged and neutral molecular clusters at ambient conditions to monitor the first steps of NPF and nanoparticle growth in the atmosphere. From studies carried out over the past years, it is evident that sulfuric acid and ammonia are important precursor gases that contribute to an acid-base stabilized nucleation mechanism. Recently, also amines and highly oxidized organic compounds have emerged as potentially significant contributors to NPF and particle growth. The studies carried out so far have substantially increased understanding of atmospheric NPF. However, it remains unclear if the currently used instrumentation detects the complete core of the nucleated clusters with all bonded ligands. So far no water ligands were found in the detected clusters. The question arises if only the more loosely bonded water ligands are lost in the inlet and ion transfer unit of current instruments or if also more strongly bonded compounds lost? This is of special importance in systems involving oxidized organic compounds since it is assumed that these compounds are less strongly bond to the acid-base stabilized core but stronger than for example water molecules. Ultimately, this means that the chemical composition of all clusters that actually take part in the atmospheric nucleation process is only partially resolved and we still lack understanding the basic building blocks of the clusters. Here we suggest detailed investigations of the clusters taking part in atmospheric NPF to identify the basic building blocks (equivalent to the strongly bonded core with ligands) of the still unknown clusters. So far, the currently used high resolution time-of-flight (TOF) mass spectrometers offer too low mass resolution for the unambiguous identification of the clusters involved in atmospheric NPF. We will use a prototype instrument that was recently developed at the University of Innsbruck. The nanoTOF features an implemented Collision Induced Dissociation cell (CID-cell) and an integrated Axial ion Mobility Classification (AMC). The combination of these two features with a state-of-the art high resolution TOF mass spectrometer allows for a stepwise release / dissociation of the weakest bonded shell of ligands (such as water molecules) and will allow the identification of the building blocks of the clusters participating in NPF. The nanoTOF will be characterized and improved during laboratory test measurements and used in several field measurement campaigns, especially in the framework of the CLOUD (Cosmics Leaving OUtdoor Droplets) collaboration at CERN and in cooperation with the University of Helsinki at the Hyytiälä forestry station. The proposed project would allow, for the first time, a detailed step-by-step analysis of the clusters participating in NPF and will enable understanding the basic mechanisms of cluster formation in atmospheric NPF. Accordingly, the expected results of the proposed project will provide new knowledge to provide model studies with new data to establish a better, in-depth understanding of the nucleation process and particle growth and its further impact on global climate.

The research project "Chemical composition of atmospheric clusters" targeted questions related to the basic mechanisms contributing to atmospheric new particle formation (nucleation) by using a novel, prototype mass spectrometer. The ultimate goal of the project was to solve the ambiguity whether the so far used instrumentation could fully depict the processes of atmospheric new particle formation on the molecular level. The collaboration with the University spin-off IONICON Analytik GmbH, lead to the development of a new instrument, the so-called ioniAPiTOF. The novel ion transfer unit used in this instrument allows for a much wider accessible mass window compared to other established instruments. Also, we were able to show that it is possible to transfer cluster ions with much lower binding energies without significant fragmentation than that is estimated for other instruments (Leiminger et al., 2019). Another important outcome of this project is related to an interdisciplinary collaboration with the department of zoology of the University of Innsbruck: our analytical instrument originally developed for the analysis of atmospheric and environmental relevant nano-particles, now offered a solution for an analytical challenge in zoology (Dvorak et al., 2019). Leiminger, M., Feil, S., Mutschlechner, P., Ylisirniö, A., Gunsch, D., Fischer, L., Jordan, A., Schobesberger, S., Hansel, A., Steiner, G. (2019) Characterisation of the transfer of cluster ions through an atmospheric pressure interface time-of-flight mass spectrometer with hexapole ion guides. Atmos. Meas. Tech., 12, 5231-5246, 2019; https://doi.org/10.5194/amt-12-5231-2019 Dvorak, M., Schnegg, R., Salvenmoser, W., Palacios, Ò., Lindner, H., Zerbe, O., Hansel, A., Leiminger, M., Steiner, G., Dallinger, R., Lackner, R. (2019) Distinct pathways for zinc metabolism in the terrestrial slug Arion vulgaris. Sci Rep 9, :20089 (2019); doi:10.1038/s41598-019-56577-7