the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Biological and dust aerosol as sources of ice nucleating particles in the Eastern Mediterranean: source apportionment, atmospheric processing and parameterization
Abstract. Aerosol-cloud interactions in mixed-phase clouds (MPCs) are one of the most uncertain drivers of the hydrological cycle and climate change. A synergy of in-situ, remote sensing and modelling experiments was used to determine the source of ice nucleating particles (INPs) for MPCs at Mount Helmos in the Eastern Mediterranean. The influences of boundary layer turbulence, vertical aerosol distributions and meteorological conditions were also examined. When the observation site is in the Free Troposphere (FT), approximately 1 in 106 aerosol particles serve as INPs. The INP abundance spans three orders of magnitude and increases following the order of marine aerosols, continental aerosols, and finally, dust plumes. Biological particles are important INPs observed in continental and marine aerosols, whereas they play a secondary yet important role even during Saharan dust events. Air masses in the planetary boundary layer (PBL) show both enriched INP concentrations and higher proportion of INPs in comparison to total aerosol particles, different from cases in the FT. The presence of precipitations/clouds enriches INPs in the FT but decreases INPs in the PBL. Additionally, new INP parameterizations, incorporating the ratio of fluorescent-to-nonfluorescent or coarse-to-fine particles and predicting >90 % of the observed INPs within an uncertainty range of a factor of 10, exhibit better performance than current widely-used parameterizations, and allow ice formation in models to respond to variations in dust and biological particles. The improved parameterizations can help MPC formation simulations in regions with various INP sources or different regions with prevailing INP sources.
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RC1: 'Comment on egusphere-2024-511', Anonymous Referee #1, 20 Mar 2024
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The manuscript presents results of an aerosol measurement campaign lasting seven weeks in autumn 2021 at a mountain site on the Peloponnese. Eight contrasting situations were observed during this campaign and characterised using a range of instruments, including an expansion chamber capable to determine in 6-minute intervals the number of ice nucleating particles (INPs) active at around -25 °C. In addition, INPs active at warmer temperatures were collected on filters for offline analysis. Planetary boundary layer height, clouds and rain were observed from a station 0.5 km below the aerosol measurements and potential source regions of the aerosol particles were derived by modelling efforts.
A wealth of data is comprehensively analysed, meaningfully interpreted and discussed in the context of the available literature. Notwithstanding that it encompasses 39 pages of main text the manuscript is pleasant to read, also Figures and Tables are clear.
There is little I would recommend to change in this manuscript. My main concern are general statements about INPs in which their activation temperature is not mentioned. In this study, INPs include those measured by PINE (ca. -25 °C) and others measured by INSEKT (-5 °C to -25 °C). Througout the text, it should always be clear which activation temperature applies in a statement. A first example is in the Abstract, line 25: "...approximately 1 in 10^6 aerosol particles serve as INPs." A much later example is on page 30, lines 753 and 754: "Therefore, the overall effect of precipitation/clouds on INPs observed at (HAC)2 shows a decrease when (HAC)2 lies within the PBL." It should be made clear that this finding relates to INPs active at around -25 °C. Testa et al. (2021; https://doi.org/10.1029/2021JD035186) made a similar observation for INPs active at around -25 °C, but at the same time INPs active at -12 °C were found to have increased (see Figure 5 in Testa et al., 2021). Hence, activation temperature matters not only in terms of the number concentration, but also in terms of atmospheric behaviour.
Minor issues
Page 5, section 2.2.1: Please add to the description of the offline INP observations the filter material, diameter, pore size, and the flow rate of the sampler.
Line 214: "40000 air parcels" probably should be "40000 particles"
Line 245: "take up a large fraction" or "make up a large fraction"?
Lines 253 and 254: "to differentiate the difference" I do not understand the meaning of this expression.
Figure 5: Please add x-axes to the plots, even if they only state the running number of observations in each type of aerosol category.
Figure 8: I wonder why the number of INPs measured with PINE does not increase with decreasing temperature. Please add a note on this issue to the Figure legend.
Figure 9a: The temperature indicated for measurements of "South dust in PBL after marine aerosols" is -2.39. I guess it should be -23.9.
Figure 9c and 9d: The effect of precipitation/clouds on INPs in FT is very similar in direction and magnitude as observed in winter in the Swiss Alps by Mignani et al. (2021; https://doi.org/10.5194/acp-21-657-2021).
Table 2: Readability of p-values would be improved by replacing the scientific notation of very small values (e.g. 9.3e-122) by "< 0.001".
Line 548 to 550: A further explanation of why values reported by Lacher et al. (2021) for Jungfraujoch (3580 m) were smaller than what was found at Mt. Helmos (2314 m) could be the higher elevation of Jungfraujoch.
Lines 588 and 589: Also in the Arctic, fluorescent particles constitute the vast majority of INPs (active at -15 °C), as Freitas et al. have recently reported (2023; https://doi.org/10.1038/s41467-023-41696-7).
Line 725: "...ABCWIBS particles are relevant for biological particles..." I am not sure what is meant by this expression. Do you mean something like "...ABCWIBS particles are related to biological particles..."
Citation: https://doi.org/10.5194/egusphere-2024-511-RC1
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