the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Hygroscopicity and CCN potential of DMS derived aerosol particles
- 1Department of Chemistry, Aarhus University, Denmark
- 2Faculty of Physics, University of Vienna, Austria
- 3Department of Applied Physics, University of Eastern Finland, Finland
- 4Faculty of Science and Technology, University of the Faroe Islands, Faroe Islands
- 5Department of Environmental Science, Stockholm University, Sweden
- 6Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University, Qatar Foundation, Doha, Qatar
- 7Division of Nuclear Physics, Lund University, Sweden
- 8Department of Environmental Science, Aarhus University, Denmark
- 1Department of Chemistry, Aarhus University, Denmark
- 2Faculty of Physics, University of Vienna, Austria
- 3Department of Applied Physics, University of Eastern Finland, Finland
- 4Faculty of Science and Technology, University of the Faroe Islands, Faroe Islands
- 5Department of Environmental Science, Stockholm University, Sweden
- 6Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University, Qatar Foundation, Doha, Qatar
- 7Division of Nuclear Physics, Lund University, Sweden
- 8Department of Environmental Science, Aarhus University, Denmark
Abstract. Dimethyl sulphide (DMS) is emitted by phytoplankton species in the oceans and constitutes the largest source of naturally emitted sulphur to the atmosphere. The climate impact of secondary particles, formed through the oxidation of DMS by hydroxyl radicals, is still elusive. This study investigates the hygroscopicity and cloud condensation nuclei activity of such particles and discusses the results in relation to their chemical composition. We show that mean hygroscopicity parameters, κ, during an experiment for particles of 80 nm in diameter range from 0.46 to 0.52 as measured at both sub- and supersaturated water vapour conditions. Ageing of the particles leads to an increase in κ from for example 0.50–0.58 over the course of 3 hours (Exp. 7). Aerosol mass spectrometer measurements from this study indicate that this change most probably stems from a change in chemical composition leading to slightly higher fractions of ammonium sulphate compared to methanesulfonic acid (MSA) within the particles with ageing time. Lowering the temperature to 258 K increases κ slightly, particularly for small particles. These κ-values are well comparable to previously reported model values for MSA or mixtures between MSA and ammonium sulphate. Particle nucleation and growth rates suggest a clear temperature dependence, with slower rates at cold temperatures. Quantum chemical calculations show that gas-phase MSA clusters are predominantly not hydrated even at high humidity conditions indicating that their gas-phase chemistry should be independent of relative humidity.
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Bernadette Rosati et al.
Status: final response (author comments only)
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RC1: 'Comment on acp-2022-188', Anonymous Referee #1, 19 Apr 2022
The study by Rosati et al. investigated nucleation, hygroscopicity, and CCN activity of secondary aerosol particles from DMS as a function of temperature and relative humidity. Important findings include reduction in nucleation and particle growth rates at lower temperature (258 K) than that at 293 K. The kappa values for CCN activity were higher for lower temperature. Considering that temperature dependent particle formation from DMS has rarely been conducted, this study will serve as a good starting point for the more detailed studies in the future. The manuscript is well written, although some figures/tables can still be improved. I suggest publication of this manuscript after addressing the following comments.
Major comments
Precursors of ammonium and nitrate
The experimental procedure (section 2.2) describes that the authors injected H2O2 and DMS. Figure S7 suggests that particles generated in the chamber contained organics, nitrate, and ammonium, in addition to sulfate and MSA. It was not clear to me how ammonia and NOx concentrations were controlled. Ammonia is especially important both for nucleation and hygroscopic processes. So, the concentration of ammonia should clearly be summarized in Table 1. It seems that the authors measured NOx concentration using a NOx analyzer. It would be helpful for readers to understand the paper if the data from the instrument were to be available.
Formation mechanisms of organic compounds and its influence on hygroscopicity/CCN activity
Figure S7 shows that the particles generated by the chamber contained 10 ~30 % of organics. I am wondering how they formed. It will be great if the authors could describe the corresponding formation mechanism. I also wondered if the organics could assist hygroscopic growth of aerosol particles. It would be great to have some additional discussion on this point.
Minor comments
Table 1
It is better to show H2O2 concentration by using mixing ratio.
Section 2.2.3
It seems that all the aerosol instruments were operated at room temperature, even though the chamber temperature was cooled down to 258 K. I wonder if potential changes in gas-particle equilibrium could be induced by the temperature change. I also wondered if the change in the equilibrium could influence the nucleation/particle growth rates in addition to chemical composition. It would be ideal to have some discussion about this point in the manuscript.
Section 2.3.5.
The authors mention that the HTDMA measurement was conducted at RH = 80%. Deliquescence relative humidity of ammonium sulfate is slightly lower than 80%. Considering the chemical composition of the particles, I personally think that it would have been better to conduct the HTDMA measurement at higher RH. Could the authors explain the reason why they selected this condition?
Figure 1a
There is a cyclic oscillation in the nucleation rate at 273 K. Is it possible to explain the potential cause?
L309 Such a size trend can be expected
I could not understand the reason why it can be expected. Please describe it in more detail.
Figure 2
It requires a lot of efforts and focus to see this figure. I suggest updating the figure so that the readers can easily get the main message of the figure.
Table 2
The formats of tables 1 nad2 are significantly different. It would be getter to have a standardized table format for a manuscript.
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RC2: 'Comment on acp-2022-188', Anonymous Referee #2, 02 May 2022
This work mainly investigated the hygroscopicity and cloud condensation nuclei activity of aerosol particles formed through oxidation of DMS. DMS is emitted by phytoplankton species in the oceans and constitutes the largest fraction of naturally emitted sulphur to the atmosphere. Secondary aerosols formed through oxidation of DMS play significant roles in climate and their hygroscopic properties are key parameters in describing their direct and indirect climate effects. Thus, scientific findings of this study are meaningful and fits well the scope of ACP. The authors have designed comprehensive laboratory chamber experiments and performed very good measurements using a suite of aerosol instruments, especially including synthesized nano-HTDMA, HTDMA, CCN and AMS measurements. In general, experiments are well designed and discussions are insightful. I have one major concern and some minor suggestions as listed below:
Major comment: As shown in Fig.S7, organic constitutes a non-negligible fraction to formed aerosol mass, but compositions and impacts of organics on hygroscopicity are not even mentioned in the discussions. It seems that authors just neglected this part of aerosol mass, and compared measured aerosol hygroscopicity only with mixed MSA-sulfate system. Authors should explain a little bit their choice in discussions or add more discussions. Also, it would be nice to discuss possible compositions of formed organics.
Minor suggestions:
L105: More details about Kappa calculations from CCN measurements should be given
L121: “further”-> “already”?
Secttion 2.3.5: set-up of the two HTDMAs are overall similar, introductions of them summarized in one paragraph might be better
Section 2.4: I suggest present an brief introduction of quantum chemical calculations and needed input parameters before 2.4.1.
L268: More discussions? Elucidate why it is interesting
L282: “higher absolute concentration”, higher-> lower?
Bernadette Rosati et al.
Bernadette Rosati et al.
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