Intercomparing different devices for the investigation of ice nucleating particles using Snomax<sup>®</sup> as test substance

Abstract

Abstract. Seven different instruments and measurement methods were used to examine the immersion freezing of bacterial ice nuclei from Snomax ® (hereafter Snomax), a product containing ice-active protein complexes from nonviable Pseudomonas syringae bacteria. The experimental conditions were kept as similar as possible for the different measurements. Of the participating instruments, some examined droplets which had been made from suspensions directly, and the others examined droplets activated on previously generated Snomax particles, with particle diameters of mostly a few hundred nanometers and up to a few micrometers in some cases. Data were obtained in the temperature range from −2 to −38 • C, and it was found that all ice-active protein complexes were already activated above −12 • C. Droplets with different Snomax mass concentrations covering 10 orders of magnitude were examined. Some instruments had very short ice nucleation times down to below 1 s, while others had comparably slow cooling rates around 1 K min −1 . Displaying data from the different instruments in terms of numbers of ice-active protein complexes per dry mass of Snomax, n m , showed that within their uncertainty, the data agree well with each other as well as to previously reported literature results. Two parameterizations were taken from literature for a direct comparison to our results, and these were a time-dependent approach based on a contact angle distribution (Niedermeier et al., 2014) and a modification of the parameterization presented in Hartmann et al. (2013) representing a time-independent approach. The agreement between these and the measured data were good; i.e., they agreed within a temperature range of 0.6 K or equivalently a range in n m of a factor of 2. From the results presented herein, we propose that Snomax, at least when carefully shared and prepared, is a suitable material to test and compare different instruments for their accuracy of measuring immersion freezing.

Use of the Single Particle Soot Photometer (SP2) as a pre-filter for ice nucleation measurements: Effect of particle mixing state and determination of SP2 conditions to fully vaporize refractory black carbon

“…The ice nucleation efficiencies of 500-nm size-selected Snomax®, NX-illite, and SRFA are shown in Figure 7. Size-selected Snomax® and NX-illite have ξ-30 > -3, and all values are in agreement 10 with previous literature (Hiranuma et al, 2015;Wex et al, 2015). The ice nucleation efficiency of SRFA has been studied in the past (O'Sullivan et al, 2014;Wang and Knopf, 2011), but no previous measurements at -30 °C have been taken with an online ice nucleation counter.…”

The micro-orifice uniform deposit impactor–droplet freezing technique (MOUDI-DFT) for measuring concentrations of ice nucleating particles as a function of size: improvements and initial validation

“…This reasonable agreement and consistency with a currently used method suggests that the MOUDI-DFT is a promising technique for measuring INP concentrations as a function of size in the atmosphere, although additional validation experiments are warranted. As different levels of agreement have been observed in past intercomparison studies depending on aerosol type Wex et al, 2015), additional intercomparison studies are needed with different aerosol types.…”

Leipzig Ice Nucleation chamber Comparison (LINC): intercomparison of four online ice nucleation counters

“…Lower FFs were measured in LACIS compared to the CSU-CFDC, and good agreement was found when particle residence times in the respective instruments were accounted for. Wex et al (2015) reported measurements on size-selected Snomax ® particles with seven instruments including LACIS and the Portable Ice Nucleation Chamber (PINC; Chou et al, 2011). Wex et al (2015) examined droplets formed on single particles and droplets taken from suspensions containing Snomax ® .…”

“…Wex et al (2015) reported measurements on size-selected Snomax ® particles with seven instruments including LACIS and the Portable Ice Nucleation Chamber (PINC; Chou et al, 2011). Wex et al (2015) examined droplets formed on single particles and droplets taken from suspensions containing Snomax ® . The varying mass of Snomax ® per droplet or per particle that was examined by the different instruments was accounted for, and the results agreed within a factor of 3 below 263 K for all instruments.…”

“…Some studies have already investigated the comparability of a number of online and offline instruments on selected aerosol types in a laboratory setting Wex et al, 2014Wex et al, , 2015Hiranuma et al, 2015;DeMott et al, 2016). Ice nucleation measurements have been conducted with the Leipzig Aerosol Cloud Interaction Simulator (LACIS; Hartmann et al, 2011, immersion mode) in parallel with the Colorado State University continuous-flow diffusion chamber (CSU-CFDC; Rogers et al, 2001b, condensation mode) on size-selected kaolinite particles including samples coated with soluble material .…”