Ice nucleus measurements: effect of site location and weather

Abstract

Filter samples of atmospheric aerosol were collected daily at a city and a rural site over an extended period. The filters were processed in an environment supersaturated with respect to ice in order to activate ice nuclei. The concentration of nuclei detected at the two sites was compared with reference to the local weather and air‐mass trajectories. The city environment generally has a larger ice nucleus concentration than the rural site. However, fluctuations in the concentrations at the two sites are usually in phase, indicating a pre‐dominantly common origin. With air‐mass trajectories over industrial regions, the nucleus concentration is increased. Local weather has a profound effect; in particular, rain and snow cause substantial reductions in ice nucleus concentration.

Natural Ice Nucleus Measurement under High Supersaturation

“…It was shown in Section 3.1 that the number concentration of ice nuclei under supersaturation and the mass concentration of particulate matter in the air tended to be higher at or just before the passage of a cold front and to fall behind it. This tendency towards ice nucleus concentration and particulate matter during the frontal passage is in agreement with the results obtained with the filter method (Al-Naimi and Saunders, 1985a;Bowdle et al, 1985). Al-Naimi and Saunders (1985a) attribute this decrease after the cold frontal passage to the precipitation scavenging and the replacement of the polluted air by the cleaner air behind the fronts.…”

“…This tendency towards ice nucleus concentration and particulate matter during the frontal passage is in agreement with the results obtained with the filter method (Al-Naimi and Saunders, 1985a;Bowdle et al, 1985). Al-Naimi and Saunders (1985a) attribute this decrease after the cold frontal passage to the precipitation scavenging and the replacement of the polluted air by the cleaner air behind the fronts. The present measurement of ice nuclei clearly shows the influence of meteorological conditions on ice nucleus concentration in the air.…”

Manchester Ice Nucleus Counter (MINC) measurements from the 2007 International workshop on Comparing Ice nucleation Measuring Systems (ICIS-2007)

“…This annular arrangement avoids the edge effects present in chambers of the flat-plate design (e.g. Al-Naimi and Saunders, 1985), and the vertical arrangement avoids gravitational loss of particles. The chamber walls are iced by pumping water into the outlet of the CFDC chamber, with the chamber having been pre-cooled to −30 • C. The chamber is quickly filled to a level 10 cm lower than the chamber inlet manifold, then is promptly pumped back out again such that during this time the wall temperatures do not rise above 0 • C. To increase the hygroscopicity of the copper wall surface, to allow a smooth ice layer to be applied, the walls were treated with an 'ebonizing' solution that reacts with the copper to form a thin layer of black cupric sulphide crystals (see Rogers et al 2001): this provides a hydrophilic surface to allow a uniform ice coating (∼0.1 mm thick -tested via the collection of melt water).…”