Abstract
Abstract. The University of Toronto continuous flow diffusion chamber (UT-CFDC) was used to study heterogeneous ice nucleation at the International Workshop on Comparing Ice Nucleation Measuring Systems (ICIS 2007) which also represented the 4-th ice nucleation workshop, on 14–28 September 2007. One goal of the workshop was to inter-compare different ice nucleation measurement techniques using the same aerosol sample source and preparation method. The aerosol samples included four types of desert mineral dust, graphite soot particles, and live and dead bacterial cells (Snomax®). This paper focuses on the UT-CFDC results, with a comparison to techniques of established heritage including the Colorado State CFDC and the AIDA expansion chamber. Good agreement was found between the different instruments with a few specific differences, especially at low temperatures, perhaps due to the variation in how onset of ice formation is defined between the instruments and the different inherent residence times. It was found that when efficiency of ice formation is based on the lowest onset relative humidity, Snomax® particles were most efficient followed by the desert dusts and then soot. For all aerosols, deposition mode freezing was only observed for T<45 K except for the dead bacteria where freezing occurred below water saturation as warm as 263 K.
Highlights
The role of ice clouds in determining the global radiation budget is not fully understood (IPCC, 2007)
Note that results from the AIDA and Colorado State University (CSU) experiments along with results from other participants in the workshop are to be presented in this special issue, and we only present a subset of these results to aid in the validation of the University of Toronto continuous flow diffusion chamber (UT-CFDC) data
For the bacteria samples we do not present an inter-comparison because of the small number of experiments performed and because most were are at T ∼ 263 K and RHw ∼100% where we believe UT-CFDC cannot distinguish between ice particles and water droplets
Summary
The role of ice clouds in determining the global radiation budget is not fully understood (IPCC, 2007). Some of the major conclusions from the third workshop were that supersaturation played an important role in determining the activation of IN, further ice nucleation measurements must completely document aerosol properties and new instruments should undergo extensive testing, controls and validation by comparison to pre-existing instruments before being implemented for atmospheric sampling (Vali, 1975). In response to these suggestions, new instruments are being validated before implementation in laboratory or field studies, for example see Stetzer et al (2008) and Kanji and Abbatt (2009b) for recent examples. Note that results from the AIDA and CSU experiments along with results from other participants in the workshop are to be presented in this special issue, and we only present a subset of these results to aid in the validation of the UT-CFDC data
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