Abstract: Accurate measurements of ice nucleation rates, and the phase or structure of the particles formed, are critical for developing reliable models of climate and atmospheric chemistry, as well as testing our understanding of the behavior of water under extreme conditions. Experiments using micron-size droplets cannot, generally, measure ice nucleation rates below ~235 K, and thus, this temperature often defines one edge of no-man’s land for supercooled water. Extensive ice nucleation rate measurements made slightly above 235 K agree quite well with each other in spite of their extreme temperature sensitivity. At much lower temperatures (180–212 K), well within no-man’s land, rate measurements can be made in nanodroplets, and in this regime, rates also agree well and are extremely insensitive to temperature. Nucleation rates measured at intermediate temperatures, ~212 K ≤ Td ≤ ~235 K, are more controversial with rates reported near 228 K differing by ~6 orders of magnitude.

This talk will summarize our recent work  that focuses on further exploring ice nucleation in this intermediate temperature regime in order to fill in the rate gap between nano- and micro-droplets. Particles are formed via condensation in supersonic nozzles and the system is characterized using a range of in situ techniques, including small-angle X-ray scattering, wide-angle X-ray scattering, infrared spectroscopy, and pressure measurements. We attempt to correct classical nucleation theory by adjusting the physical properties of water for the increasing internal pressure as the droplets decrease in size.