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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- 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.