A large source of uncertainty in current climate models arises from the poor understanding of how aerosols and cloud condensates form in the Earth atmosphere by nucleation and growth of gas phase molecular clusters (smaller than nanometers) into liquid and solid phase droplets and particles (up to many microns). The biggest issue is the nucleation step itself, which involves molecular aggregates from subnanometers to several nanometers in size. The general idea is that droplet/particle formation is initiated in a supersaturated gas by the formation of a critical cluster in that size range. The formation of the critical cluster is considered to be the rate determining step. Once formed it eventually grows into a large aerosol droplet/particle.In this talk, we present a new experiment design to study gas phase nucleation on a truly molecular level. The experimental setup combines Laval nozzle expansions to initiate vapour condensation in a controlled way with an ultrasoft aerosol sizing method that is based on mass spectrometric detection [1-3]. The unique feature of the sizing method is its ability to determine the mass and thus the size of weakly-bound clusters and ultrafine aerosols nearly destruction-free. The new experimental approach provides molecular-level information on the size and on the chemical composition of the clusters that are involved in the nucleation step. Such experimental data has the potential to improve our understanding of the molecular mechanisms of gas phase nucleation.[1] B. Schl�ppi, J. H. Litman, and R. Signorell, manuscript in preparation (2014)[2] J. H. Litman, B. L. Yoder, B. Schl�ppi, and R. Signorell, Phys. Chem. Chem. Phys., 15(3), 940-9 (2013)[3] B. L. Yoder, J. H. Litman, P. F. Forysinski, J. L. Corbett, and R. Signorell, J. Phys. Chem. Lett., 2, 2623-2628 (2011)

Gas phase nucleation on a molecular level: A new experimental approach

248th National Meeting (2014)

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