Homogeneous Nucleation of Water Anomalies Explained by Recognition and Elimination of Heterogeneous Species

A piston-type expansion cloud chamber, capable of producing short pulses of nucleation, was used to study the homogeneous nucleation of water over a wide range of temperature and supersaturation. A large effort was made to remove impurities capable of acting as heterogeneous nuclei from the system. The chamber was found to be capable of performing experiments that were relatively free of interfering impurities, and the results resolved several anomalous nucleation phenomena appearing in the literature: the knee in drop concentration vs. supersaturation data, the temperature dependence of the critical supersaturation, and the decay of the nucleation rate with time. The anomalies were found to be caused by impurities active at different temperature and supersaturation regimes.