the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 24 Aug 2026
Tropical cyclone amplifies anthropogenic influences on aerosol-cloud interactions over the South China Sea
Abstract. Tropical cyclones can influence marine aerosol-cloud interactions by transporting continental anthropogenic pollutants over the ocean. However, this process and its impact remain poorly understood due to lack of direct measurements. Using shipborne measurements over the South China Sea (SCS) from 22 June to 5 July 2022, we investigated how a typical TC Chaba altered aerosol physicochemical properties and cloud microphysical responses. As TC Chaba developed, its circulation altered regional transport pathways, shifting air masses from local marine origin to long-range transport from the Indochina Peninsula and causing pronounced increases in non-refractory submicron particulate matter (NR-PM1) concentrations. Organic aerosol (OA) increased from 14.6 % to 44.9 % of NR-PM1 after the influence of TC Chaba, mainly due to enhanced oxygenated OA (OOA) from long-range transport together with enhanced local heterogeneous oxidation, as indicated by the higher OA oxidation state and increasing OOA concentrations with Ox and relative humidity. These changes led to a ~60 % decrease in aerosol hygroscopicity (κ), while an ~27 % increase in κOA, which outweighed the modest particle size increase and resulted in a lower bulk activation ratio. Furthermore, CCN concentrations increased by up to sixfold because of enhanced aerosol concentrations. Combined observations and cloud parcel simulations indicate that the aerosol perturbations decreased cloud droplet effective radius by 11–37 % and increased the autoconversion radius by 6–26 %, enhancing cloud reflectivity and suppressing warm-rain formation. Satellite observations further confirmed smaller cloud droplets. These results demonstrate a strong TC influence on marine cloud microphysics and radiative effects.
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Status: open (until 05 Oct 2026)
- RC1: 'Comment on egusphere-2026-4265', Anonymous Referee #1, 07 Sep 2026 reply
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RC2: 'Comment on egusphere-2026-4265', Anonymous Referee #2, 13 Sep 2026
reply
Ou et al. (2026) investigated the impacts of tropical cyclones on aerosol–cloud interactions over the South China Sea based on shipborne observations. The study found that Tropical Cyclone Chaba enhanced the influence of anthropogenic emissions from the Indochina Peninsula on the physicochemical properties of aerosols over the South China Sea, which subsequently affected cloud microphysical properties. Overall, this study presents interesting and potentially important findings that are relevant to the scope of Atmospheric Chemistry and Physics. However, some aspects of the data analysis and figure presentation need further improvement to better support the main conclusions. I therefore recommend publication after the authors have adequately addressed the following comments:
Major comments:
- The authors applied the PMF method to identify the sources of organic aerosol, and one factor was identified as biomass-burning organic aerosol (BBOA) based mainly on the obvious signal at m/z 60. Although m/z 60 is widely recognized as a tracer for levoglucosan and biomass burning, the mass spectrum of this factor also shows a clear signal at m/z 58. The signals at m/z 58 and m/z 60 may also be associated with chloride and its isotopic signals, respectively. Considering the relatively small contribution of this factor, I suggest that it may instead be related to sea salt and could represent a mixture of sea-salt-related and organic aerosol components. Therefore, the identification of this factor as BBOA requires further justification.
- The pre- and post-TC observations may correspond to different locations along the cruise track, including TC-avoidance maneuvers. Spatial variability may therefore be confounded with the temporal changes attributed to TC Chaba. The selection of 28 June as the boundary between the pre-TC and post-TC periods lacks a clearly stated objective meteorological criterion, particularly because Chaba was officially named on 29 June.
- Precipitation is shown in Fig. 1, but it is not mentioned or discussed in the manuscript. The authors should briefly describe the precipitation conditions during the observation period, as precipitation can substantially reduce aerosol concentrations through wet removal and may consequently affect the observed aerosol properties and their temporal variations.
- Line 305: The attribution of enhanced OOA to heterogeneous oxidation is not adequately supported. RH, Ox, OOA and air-mass origin all covary during TC development, and their correlations do not independently distinguish local chemical formation from transport of aged OOA.
- Line 415: The simulated maximum supersaturation of approximately 0.03%–0.28% lies partly below the 0.2%–0.7% range of the CCN measurements. The applicability of measured k values to these simulated cloud conditions is therefore uncertain. The Pyrcel assumptions concerning adiabatic ascent, aerosol mixing state, modal size distributions and the use of fixed k values at 0.4% and 0.7% supersaturation introduce uncertainties that are not quantified.
- The k values represent particles near the supersaturation-dependent D50, whereas fOA is derived from bulk NR-PM1 This size mismatch introduces uncertainty into the estimated relationship between composition and hygroscopicity.
- The authors used the Pyrcel model to simulate the cloud droplet number concentration (CDNC) at cloud base; however, the simulation results are not presented in the manuscript. The authors should include the simulated CDNC results in Fig. 5, preferably together with the NCCN results, to allow readers to assess the model performance and better understand the effects of aerosol properties on cloud microphysics.
- The MODIS “Cloud particle size liquid” product is not necessarily equivalent to modeled cloud-droplet effective radius. The satellite averaging domain is also substantially larger than the ship-observation footprint. The pre/post-TC difference in MODIS cloud particle size may be associated with changes in cloud type, updraft velocity, liquid-water path, cloud-top height, precipitation or TC dynamics rather than aerosol effects.
- What is the specific definition of rc? The manuscript only presented the calculation method, but it does not clearly define this parameter.
- The study is based on a single TC event without an independent control period, but the manuscript repeatedly uses causal language implying that TC Chaba directly produced the observed aerosol and cloud changes.
Minor comments:
- Line 161: The format of the citation “Petters and Kreidenweis (2007)” here should be “(Petters and Kreidenweis, 2007)”.
- Some references are duplicated, while others contain incomplete or inconsistent bibliographic information. For example, the following reference appears twice:
- Lines 145: The text contains the duplicated citation “Ng et al., 2011.Ng et al. (2011).”
- Lines 167–168: The wording “it is noting” is grammatically incorrect.
- The precise MODIS variable name, retrieval wavelength, quality-control criteria and valid-pixel coverage are not reported.
- Lines 430–440: “Cloud particle size,” “cloud droplet size” and “effective radius” are used as though they were interchangeable quantities.
Citation: https://doi.org/10.5194/egusphere-2026-4265-RC2
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- 1
This manuscript investigates the impact of a tropical cyclone on aerosols, cloud condensation nuclei activity, and cloud microphysics over the South China Sea, utilizing a combination of shipborne observations, satellite data, and 0-D cloud parcel model simulations. The results demonstrate that the tropical cyclone amplifies the influence of anthropogenic emissions on aerosol-cloud interactions within this region. These findings are interesting and advance understanding of aerosol-cloud interactions under specific weather conditions. I recommend this manuscript for publication after addressing the following comments:
Major comments:
1. The authors demonstrate that the tropical cyclone amplified the anthropogenic influence on aerosol cloud interactions over the South China Sea, which is evidenced by the observed increase in organic aerosol concentrations and backward trajectories. However, tropical cyclone-induced precipitation simultaneously leads to the aerosol wet scavenging. Could the authors clarify the spatial extent of the impacts driven by both the precipitation scavenging and the circulation-induced enhancement of anthropogenic influences? Alternatively, it would be highly beneficial to include a brief discussion on this matter in the manuscript.
2. The authors conducted a Positive Matrix Factorization (PMF) analysis on organic aerosols; however, the manuscript lacks a description of how the resolved factors were defined. The authors should first detail the identification process and criteria used to determine the distinct primary organic aerosol and secondary organic aerosol factors before proceeding to discuss their characteristics and implications.
3. In the 0-D cloud Pyrcel model simulations, the authors state that 'κ at 0.7% SS and 0.4% SS were assumed to represent hygroscopicity of the Aitken and accumulation modes, respectively.' Are there relevant references to support the assumption that supersaturations of 0.7% and 0.4% adequately represent the state of Aitken and accumulation mode particles? Alternatively, could the authors explain why selecting these specific supersaturation levels to represent these two modes.
4. Furthermore, since the updraft velocity could not be directly measured, the authors prescribed a range of 0.1-2 m s⁻¹ for the simulations based on literature reporting conditions approximately 400 km from the tropical cyclone center. The authors justify this by noting that the minimum distance between the research vessel and the tropical cyclone was 400 km. However, is this updraft velocity range still representative at greater distances? The authors should address and clarify this point in the manuscript.
5. I noticed that the time series of the aerosol chemical composition measured by the ACSM exhibits several data gaps. However, the manuscript does not provide an explanation for these missing data periods. The authors are requested to add a brief clarification regarding these discontinuities.
6. Section 3.2 details the linear parameterization between aerosol hygroscopicity and the organic mass fraction. The slope obtained under marine influence during the pre-TC period is noted to be lower than that reported for remote marine environments. It would be helpful to explicitly state in the discussion if this implies a consistently higher background of anthropogenic or ship-related emissions in the SCS even prior to the direct influence of the tropical cyclone.
Specific comments:
1. In the methodology section, the various methods are presented together without clear divisions, which makes it quite difficult for readers to follow. The authors are requested to divide this section into appropriate subsections with clear headings to improve readability and organization.
2. Please ensure that all mathematical variables within the equations and the surrounding text (e.g., R, T) are italicized consistently to strictly adhere to ACP formatting guidelines.
3. Line 276: The name of tropical cyclone is wrong.
4. Line 161: The format of citation is wrong.
5. Line 196: The location of citation is wrong.
6. Line 246: The symbol “P” should be italicized. Please check the whole manuscript carefully.
7. Line 256: The location of the citation is wrong again, lease check the whole manuscript carefully.