the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 17 Aug 2026
Immersion freezing of surface dust particles from Tengger Desert in China: effects of mineral composition and aging treatments on ice nucleating activity
Abstract. Mineral dust is a major source of ice nucleating particles (INPs) for mixed-phase clouds and thereby influences cloud properties, precipitation, and radiative forcing. However, the ice nucleation properties of natural dust and their response to atmospheric aging remain poorly constrained. Here, we investigated immersion freezing (IMF) of surface-collected dust from Tengger Desert, China, and examined the effects of internal mixing with ammonium sulfate (AS), NaCl, H2SO4, and HNO3, as well as heat treatment. Median freezing temperature (T50) of Tengger Desert dust increased from 251.6 K to 256.7 K as dust mass fraction increased from 1.4x10-4 wt% to 1.0x10-1 wt%. A minor increase in feldspar content (~2 % in surface area) quantified by single particle analysis enhanced the ice nucleation active site density (Ns) by approximately one order of magnitude. Internal mixing with AS enhanced IMF activity, with the enhancements of T50 (0.4 K – 4.8 K), Ns, and heterogeneous ice nucleation rate coefficient (Jhet) exhibiting sigmoidal response to AS concentration from 5x10-5 M to 5x10-2 M. This enhancement is attributed to NH4+ adsorption on dust surface. NaCl and acids, as well as heat treatment, had no impact on the overall IMF activity in terms of T50, although modest changes in Ns and Jhet were observed above 256 K. We developed the experimentally constrained parameterizations of Ns and Jhet for Tengger Desert dust with and without aging, which can be used in cloud modeling to improve our understanding of how atmospheric aging modifies the ice nucleation of natural dust.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics. The peer-review process was guided by an independent editor, and the authors also have no other competing interests to declare.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: closed
- RC1: 'Comment on egusphere-2026-3953', Anonymous Referee #1, 07 Sep 2026
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RC2: 'Comment on egusphere-2026-3953', Anonymous Referee #2, 20 Sep 2026
Authors have investigated immersion freezing (IMF) of surface-collected dust from Tengger Desert, China, and examined the effects of internal mixing with ammonium sulfate (AS), NaCl, H2SO4, and HNO3, as well as heat treatment. The effects of increase in dust mass fraction on Median freezing temperature (T50) of Tengger Desert dust have been shown while no effect of NaCl and acids (H2SO4 and HNO3), as well as heat treatment in terms of T50, on the overall IMF activity, was noted.
Limited understanding on impacts of chemical aging on ice nucleation for airborne dust is available. The experimentally constrained parameterizations of Ns and Jhet for Tengger Desert dust with and without aging presented in this study may be used in cloud modeling to further understand that how atmospheric aging modifies the ice nucleation of natural dust. Overall, the work is extensive and may be accepted after minor revision. Following are the specific comments:
- The whole manuscript revolves around comparison of IMF characteristics in normal dust and sonicated dust. Specific details of sonication treatment (temperature at which ultrasonication was done, make and model of ultrasonicator used for the purpose etc) may be provided. Further authors may explain that why 30 min sonication is preferred.
- Why cooling rate of 10 K.min⁻¹ has been used? Appropriate reference for this may be provided. What is the advantage of doing this instead of usual 2 K.min-1 or 1 K.min-1
- L359: Increase in AS concentration and activation of the ice nucleation sites needs more explanation.
- L437: Pl see usage of potential in sentence- NH4+ adsorbed on dust surfaces potential can alter the arrangement.
- Why most effects of acid treatments have been reported on Us-dust only and not on S-dust?
- Heat treatment is the most common step for IMF study. Authors may elaborate upon the section pertaining to the effects of heat treatment. Heat treatment effect on S-dust is missing. Further, for Us-dust, loss of ice active sites at warm temperatures and change in T50 is reported while no discussion on change in profile has been included.
- Aging is a very wide process which includes internal mixing /coating with organic as well as inorganic components. However, the focus of this manuscript is on inorganic processes only but authors may add a section stating limitation and may be counter effect of aging where organics are involved.
Citation: https://doi.org/10.5194/egusphere-2026-3953-RC2 - AC1: 'Comment on egusphere-2026-3953', Bingbing Wang, 15 Oct 2026
Status: closed
-
RC1: 'Comment on egusphere-2026-3953', Anonymous Referee #1, 07 Sep 2026
Xue et al. investigate immersion freezing of surface dust from the Tengger Desert and examine the effects of ammonium sulfate, NaCl, acids, and heating. The dataset is extensive. The combination of freezing measurements and single-particle analysis is useful.
Overall, I think the study is suitable for publication after minor revision. My main concerns are related to the interpretation of the mineralogical effects, the calculation of particle surface area, and several mechanistic claims that are stronger than supported by the measurements.
Major Comments:
- The authors attribute the higher ice nucleation activity of Us-dust mainly to a ~2% increase in feldspar fraction. They further state that this increase “resulted in” a ~2 K increase in T50 and an order-of-magnitude increase in Ns. However, it is difficult to find and establish such a causal relationship. The data are consistent with an important contribution from feldspar, but they do not quantitatively demonstrate that the 2% increase in feldspar alone caused the observed enhancement. The authors should use more cautious wording.
- Ns is central to the manuscript. However, the surface area is estimated from CCSEM/EDX measurements of aerosolized particles, mainly between approximately 0.2 and 2 µm, whereas the original dust was sieved to <74 µm. Nebulization, transport, and impaction can strongly bias the measured particle-size distribution, particularly for larger particles and aggregates. It is therefore not obvious that the CCSEM population accurately represents the particles present in the 1 µL freezing droplets. An independent measurement of the suspension particle-size distribution would be very helpful. Additionally, it’s important to clearly state that the surface area used here is a physical/geometric surface area derived from CCSEM particle size, rather than a BET specific surface area. This distinction is important because many literature Ns datasets and parameterizations use BET-derived surface area. Direct comparison of Ns values may therefore not be strictly equivalent.
- The mechanism proposed for ammonium sulfate is too strong. The observed enhancement is consistent with mechanisms proposed in previous studies, but several mechanisms may contribute. Please change statements such as “directly support” to more cautious language unless additional surface characterization is provided.
- Line 208: Please justify the use of a cooling rate of 10 K/min, which is substantially faster than the ~1 K/min commonly used in droplet-freezing studies. Such a rapid cooling rate may increase thermal lag and temperature uncertainty, and can also affect the derived Jhet. Please explain why 10 K/min was chosen and clarify how the stated temperature uncertainty of ±0.5 K was validated under this dynamic cooling condition.
- Section 4: The proposed AS-dependent parameterization is potentially useful, but it is derived from one surface dust sample and one aqueous treatment protocol. The atmospheric example is illustrative, but it gives the impression that the parameterization can already be directly implemented for internally mixed atmospheric dust. I suggest describing this as an experimentally constrained sensitivity parameterization rather than a generally applicable atmospheric aging parameterization.
Specific comments:
- Methods state 95 °C for 30 min, while it states 90 °C for 30 min in Line 496. Please correct this.
- Section 3.5.4: The present heat treatment is very different from 523 K for 4–5 h (Zolles et al., 2015). These treatments may affect different components. Therefore, the comparison with Zolles et al. needs care.
- Line 141: Please clarify what is meant by “ultrapure water” here. It would be helpful to provide the water source/system and relevant water-quality information.
- Line 425: Typo “felspar”.
Citation: https://doi.org/10.5194/egusphere-2026-3953-RC1 -
RC2: 'Comment on egusphere-2026-3953', Anonymous Referee #2, 20 Sep 2026
Authors have investigated immersion freezing (IMF) of surface-collected dust from Tengger Desert, China, and examined the effects of internal mixing with ammonium sulfate (AS), NaCl, H2SO4, and HNO3, as well as heat treatment. The effects of increase in dust mass fraction on Median freezing temperature (T50) of Tengger Desert dust have been shown while no effect of NaCl and acids (H2SO4 and HNO3), as well as heat treatment in terms of T50, on the overall IMF activity, was noted.
Limited understanding on impacts of chemical aging on ice nucleation for airborne dust is available. The experimentally constrained parameterizations of Ns and Jhet for Tengger Desert dust with and without aging presented in this study may be used in cloud modeling to further understand that how atmospheric aging modifies the ice nucleation of natural dust. Overall, the work is extensive and may be accepted after minor revision. Following are the specific comments:
- The whole manuscript revolves around comparison of IMF characteristics in normal dust and sonicated dust. Specific details of sonication treatment (temperature at which ultrasonication was done, make and model of ultrasonicator used for the purpose etc) may be provided. Further authors may explain that why 30 min sonication is preferred.
- Why cooling rate of 10 K.min⁻¹ has been used? Appropriate reference for this may be provided. What is the advantage of doing this instead of usual 2 K.min-1 or 1 K.min-1
- L359: Increase in AS concentration and activation of the ice nucleation sites needs more explanation.
- L437: Pl see usage of potential in sentence- NH4+ adsorbed on dust surfaces potential can alter the arrangement.
- Why most effects of acid treatments have been reported on Us-dust only and not on S-dust?
- Heat treatment is the most common step for IMF study. Authors may elaborate upon the section pertaining to the effects of heat treatment. Heat treatment effect on S-dust is missing. Further, for Us-dust, loss of ice active sites at warm temperatures and change in T50 is reported while no discussion on change in profile has been included.
- Aging is a very wide process which includes internal mixing /coating with organic as well as inorganic components. However, the focus of this manuscript is on inorganic processes only but authors may add a section stating limitation and may be counter effect of aging where organics are involved.
Citation: https://doi.org/10.5194/egusphere-2026-3953-RC2 - AC1: 'Comment on egusphere-2026-3953', Bingbing Wang, 15 Oct 2026
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Xue et al. investigate immersion freezing of surface dust from the Tengger Desert and examine the effects of ammonium sulfate, NaCl, acids, and heating. The dataset is extensive. The combination of freezing measurements and single-particle analysis is useful.
Overall, I think the study is suitable for publication after minor revision. My main concerns are related to the interpretation of the mineralogical effects, the calculation of particle surface area, and several mechanistic claims that are stronger than supported by the measurements.
Major Comments:
Specific comments: