How CO2 gas accelerates water nucleation at low temperature.

We conducted homogeneous nucleation experiments for dilute binary H2O-CO2 mixtures in Ar-N2 carrier gas with different CO2/H2O ratios at temperatures of 57 and 75 K and total pressures of ∼40 and 70 Pa, respectively. Direct experimental information on the number and type of molecules in the clusters and on the cluster number concentration is obtained by mass spectrometric detection of nucleating clusters that form in the uniform region of Laval expansions. Only homo-molecular water clusters are observed in the mass spectra.