the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
The Fifth International Workshop on Ice Nucleation Phase 3 (FIN-03): Field Intercomparison of Ice Nucleation Measurements
Abstract. The third phase of the Fifth International Ice Nucleation Workshop (FIN-03) was conducted at Storm Peak Laboratory in Steamboat Springs, Colorado in September 2015 to facilitate the intercomparison of instruments measuring ice nucleating particles (INPs) in the field. Instruments included a subset of two online and four offline measurement systems for INPs, a subset of those utilized in the laboratory study that comprised the second phase of FIN (FIN-02). Composition of total aerosols were characterized by the Particle Ablation by Laser Mass Spectrometry (PALMS) and Wideband Integrated Bioaerosol Sensor (WIBS) instruments, and aerosol size distributions were measured by a Laser Aerosol Spectrometer (LAS). The dominant total particle compositions present during FIN-03 were composed of sulfates, organic compounds, and nitrates, as well as particles derived from biomass burning. Mineral dust containing particle types were ubiquitous throughout and represented 67 % of supermicron particles. Total WIBS fluorescing particle concentrations for particles with diameter > 0.5 µm were 0.04±0.02 cm-3 (0.1 cm-3 highest, 0.02 cm-3 lowest), typical for the warm season in this region and representing ~9 % of all particles in this size range as a campaign average.
The primary focus of FIN-03 was the measurement of INP concentration via immersion freezing at temperatures > –33 °C. Additionally, some measurements were made in the deposition nucleation regime at these same temperatures, representing one of the first efforts to include both mechanisms within a field campaign. INP concentrations via immersion freezing reported by all ice nucleation instruments generally agreed to within one order of magnitude for measurement and sampling times coordinated to within three hours. Sometimes, much better agreement was obtained. Outliers of up to two orders of magnitude occurred between –25 °C and –18 °C; better agreement was seen at higher and lower temperatures. INP activity in the immersion freezing mode was generally found to be an order of magnitude or more efficient than in the deposition regime at 95–99 % water relative humidity, although this limited data set should be augmented in future efforts.
To contextualize the study results an assessment was made of the composition of INPs during the late Summer to early Fall period of this study, inferred through comparison to existing ice nucleation parameterizations and through measurement of the influence of thermal and organic carbon digestion treatments on immersion freezing ice nucleation activity. Consistent with other studies in continental regions, biological INPs dominated at temperatures > –20 °C and sometimes colder, while arable dust-like or other organic-influenced INPs were inferred to dominate at most times below –20 °C.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2024-1744', Anonymous Referee #1, 19 Aug 2024
This manuscript is well written. The authors conducted a fair intercomparison of online and offline INP-measuring instruments in the field. Despite the challenging environment at SPL, invaluable outcomes and lessons are reported in a neutral and unbiased manner. Furthermore, the authors include a list of limitations (e.g., deviation in sampling particle sizes etc.) and things to be further explored in this manuscript for more understanding of aerosol-cloud interactions (e.g., a need for online/direct deposition ice nucleation measurements), which are important messages to the INP research community. This reviewer agrees that more research is necessary to predict and explain the temporal variation of biological INPs (perhaps in a predominantly biogenic environment). While the authors found a predominant contribution of mineral and/or other inorganic particles to INP abundance in this study, they also note the need for in situ mixed INP detection and characterizations, especially for Soil & BBA INPs, which is important. The study topic is relevant to the journal scope of AMT. This reviewer supports the publication of this paper in AMT after the authors address several questions below.
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Questions
[1] Figure 7: This reviewer wonders if using 3-hr INP median or log-average changes any conclusions of this intercomparison study. The ratio in Fig. 7 is computed by using time averages, which is reasonable. But, since the reported NINP spans a log range at a majority of freezing temperatures examined in this study, the average can be biased by high NINP values at the given temperature, such as the ones from FRIDGE-CS and CSU-IS. Perhaps, using the median may overall result in better agreement for NC State(F), NC State(I), and CSU-CFDC? The same average vs. median argument applies Figs. 8 & 9.
[2] Figure 5: This reviewer wonders why NC State CS(F) shows a lower detection of NINP (~6 x 10-3 L-1) than NC State CS(I) (~10-1 L-1). The sampling air flow rate seems similar for these two methods as described in Sect. 2.2.2. The sampling interval was shorter for impinger sampling? Or it may be due to the difference in collected particle sizes (L836-839; L846-848; L855-858)? This reviewer is aware of a general statement in L865-870.
[3] P31L649-655: Low AE (<1) seen in 9/14-16 in Fig. 3b may be due to the predominance of large dust seen in Fig. 4? The authors also report that the submicron particles dominated during the study period (L-637-638). The effective aerosol scattering efficiency from SPL during this intercomparison campaign can be similar to what is reported in Testa et al. (2021)?
Refs.
Russell. P. B. et al., ACP, 10, 1155-1169, https://doi.org/10.5194/acp-10-1155-2010, 2010.
Testa, B. et al. JGR-A, 126, e2021JD035186. https://doi.org/10.1029/2021JD035186, 2021.
[4] P49L971-973: Can the authors clarify this part?
Comments
P37L749-750: This is good. Comparability of impinger and filter-based methods shown in this work implies that ambient particles collected on filters are well-scrubbed in liquid suspension for freezing tests on NC State CS, resulting in comparable NINP to that from directly suspended impinger samples, for this field study at least.
P44L885-887: This recaps that the link between aerosol chemical composition and INP is not straightforward and underscores the importance of ice residual composition data.
P64L1249-1255: This reviewer agrees. The ultimate future INP instrument intercomparison may be performed on the aircraft platform in cirrus and/or pyrocumulonimbus cloud regimes with collocated aerosol instruments suggested by Burrows et al. onboard then.
Citation: https://doi.org/10.5194/egusphere-2024-1744-RC1 - AC2: 'Reply on RC1', Paul DeMott, 05 Nov 2024
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RC2: 'Comment on egusphere-2024-1744', Anonymous Referee #2, 20 Aug 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1744/egusphere-2024-1744-RC2-supplement.pdf
- AC3: 'Reply on RC2', Paul DeMott, 05 Nov 2024
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RC3: 'Comment on egusphere-2024-1744', Gabor Vali, 22 Aug 2024
- AC1: 'Reply on RC3', Paul DeMott, 05 Nov 2024
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