Contact freezing: a review of experimental studies

Abstract

Abstract. This manuscript compiles both theoretical and experimental information on contact freezing with the aim to better understand this potentially important but still not well quantified heterogeneous freezing mode. There is no complete theory that describes contact freezing and how the energy barrier has to be overcome to nucleate an ice crystal by contact freezing. Experiments on contact freezing conducted using the cold plate technique indicate that it can initiate ice formation at warmer temperatures than immersion freezing. Additionally, a qualitative difference in the freezing temperatures between contact and immersion freezing has been found using different instrumentation and different ice nuclei. There is a lack of data on collision rates in most of the reported data, which inhibits a quantitative calculation of the freezing efficiencies. Thus, new or modified instrumentation to study contact nucleation in the laboratory and in the field are needed to identify the conditions at which contact nucleation could occur in the atmosphere. Important questions concerning contact freezing and its potential role for ice cloud formation and climate are also summarized.

Ice nucleation efficiency of AgI: review and new insights

“…Originally, contact freezing referred to freezing initiated by the collision of an aerosol particle with a supercooled droplet (Ladino Moreno et al, 2013). This view of collisional contact freezing has been complemented by Durant and Shaw (2005), who found higher ice nucleation temperatures compared with the immersion mode when an ice nucleus was in contact with the water-air interface of a droplet, from either the inside or the outside Gurganus et al, 2014;Fornea et al, 2009;Murray et al, 2012;Shaw et al, 2005).…”

Comparing contact and immersion freezing from continuous flow diffusion chambers

“…In contact freezing the INP collides with the droplet followed by freezing. Contact freezing (CF) in the original sense is understood as the process in which freezing of a supercooled droplet results from the collision with an aerosol particle (Ladino Moreno et al, 2013;Vali, 1985). This view of collisional contact freezing has been complemented by Durant and Shaw (2005), who found a higher ice nucleation temperature compared with the immersion mode, when an INP was in contact with the waterair interface of a droplet, from either the inside or the outside Gurganus et al, 2014;Fornea et al, 2009;Murray et al, 2012;Shaw et al, 2005).…”

“…Ladino Moreno et al (2013) reviewed experimental studies on contact freezing and also pointed out large discrepancies in the available experimental data. Quantification of the number of INPs required for contact freezing, the time dependence of contact freezing, and dependence on particle type and size were listed amongst the most uncertain parameters.…”

“…The too large values of the freezing efficiency were attributed to the overestimation of droplet size in calculating collision efficiency. They also mistook liquid droplets for frozen droplets because multiple droplets were simultaneously present in the laser beam of the detector (Ladino Moreno et al, 2013).…”

A new electrodynamic balance (EDB) design for low-temperature studies: application to immersion freezing of pollen extract bioaerosols

“…Murray et al, 2010;Knopf et al, 2011;Kanji et al, 2013;Hoffmann et al, 2013a;Atkinson et al, 2013.) Summaries of previous results, obtained by both laboratory work and fieldwork, and the atmospheric implications of these studies are provided by several recent review articles, and no further detail is given here (Laaksonen et al, 1995;Pöschl, 2005;Hoose and Möhler, 2012;Murray et al, 2012;Ladino Moreno et al, 2013). It is noted that several studies suggest that IN processes are still not sufficiently Published by Copernicus Publications on behalf of the European Geosciences Union.…”