Comparative measurements of ambient atmospheric concentrations of ice nucleating particles using multiple immersion freezing methods and a continuous flow diffusion chamber

Abstract

Abstract. A number of new measurement methods for ice nucleating particles (INPs) have been introduced in recent years, and it is important to address how these methods compare. Laboratory comparisons of instruments sampling major INP types are common, but few comparisons have occurred for ambient aerosol measurements exploring the utility, consistency and complementarity of different methods to cover the large dynamic range of INP concentrations that exists in the atmosphere. In this study, we assess the comparability of four offline immersion freezing measurement methods (Colorado State University ice spectrometer, IS; North Carolina State University cold stage, CS; National Institute for Polar Research Cryogenic Refrigerator Applied to Freezing Test, CRAFT; University of British Columbia microorifice uniform deposit impactor-droplet freezing technique, MOUDI-DFT) and an online method (continuous flow diffusion chamber, CFDC) used in a manner deemed to promote/maximize immersion freezing, for the detection of INPs in ambient aerosols at different locations and in different sampling scenarios. We also investigated the comparability of different aerosol collection methods used with offline immersion freezing instruments. Excellent agreement between all methods could be obtained for several cases of co-sampling with perfect temporal overlap. Even for sampling periods that were not fully equivalent, the deviations between atmospheric INP number concentrations measured with different methods were mostly less than 1 order of magnitude. In some cases, however, the deviations were larger and not explicable without sampling and measurement artifacts. Overall, the immersion freezing methods seem toPublished by Copernicus Publications on behalf of the European Geosciences Union. , although more comparisons are needed in this temperature regime that is difficult to access with online methods. Relative to the CFDC method, three immersion freezing methods that disperse particles into a bulk liquid (IS, CS, CRAFT) exhibit a positive bias in measured INP number concentrations below −20 • C, increasing with decreasing temperature. This bias was present but much less pronounced for a method that condenses separate water droplets onto limited numbers of particles prior to cooling and freezing (MOUDI-DFT). Potential reasons for the observed differences are discussed, and further investigations proposed to elucidate the role of all factors involved.

Characteristics of Ice Nucleating Particles in and Around California Winter Storms

“…However, again, there was considerable scatter in the data, especially for the CFDC measurements, indicating that changes in measured n INP were driven by variability in overall concentration, and not just processing temperature during this study. As with previous studies (DeMott et al, ), we also observed good agreement, in general, between n INP measured by the CFDC and the IS, with the respective cloud of values falling on top of each other in the region of overlapping temperatures. Figure also shows the CFDC data measured from the G‐1 during the CalWater 2011 campaign, hereafter CalWater‐1 (blue circles).…”

Characterization of Ice‐Nucleating Particles Over Northern India

“…The variability was not systematic, that is, showing one technique always being lower than another technique. A similar conclusion was reached by DeMott et al () for an intercomparison using ambient aerosol. This suggests that the precision of cold‐stage derived INP concentration is not better than 1 order of magnitude.…”

Marine and Terrestrial Organic Ice‐Nucleating Particles in Pristine Marine to Continentally Influenced Northeast Atlantic Air Masses

“…also includes n INPs measured by the HINC-EV (ALL) and DFPC (CLEAN sector only). HINC-EV measurements of n INPs, À30°C fall within an order of magnitude of n INPs estimated from an extrapolation of the IS INP spectra to colder temperatures(Figure 4a), indicating good method agreement based on recent comparisons between ice nucleation measurement techniques(DeMott et al, 2017). At À22°C in the CLEAN sector, the…”