In this study, the authors show that organosulfates (OSs), in particular some C2–C3 OSs and isoprene-/monoterpenes-derived OSs, can represent a potentially important source of marine organic aerosols during summer time. In marine atmospheres, influences of marine emissions and continental outflows across different seasons can potentially determine the variation of OSs concentrations and their relative concentrations. The findings of this work provide better insights into the atmospheric sources of OSs. The paper is well written and the results are well presented and discussed. I have some minor comments below .

Comments

Line 75, “Each aerosol sample was collected for 10−24 hrs, and a field blank sample was collected during each cruise.” For the sample collection, any sampling artifacts for the OSs and other species collection? 

Can the authors comment what are the chemical stability of these quantified OSs in the atmosphere?

Line 119, “The total quantified OSs and nitrooxy-OSs ranged from 4.5 to 109.1 ng/m³ in marine aerosols during the shipboard120 observations over the YBS (Fig. 1, Table S1). The eleven quantified OS and NOS compounds contributed 0.1%−3.2%of the OA mass concentrations over the YBS.” What the measurement uncertainty of the concentrations of these quantified OSs? 

Line 123, “This was due to the active interactions between biogenic VOCs and sulfate aerosols under high RH conditions in coastal areas, which favored the aqueous-phase formation of OSs the atmosphere” Can the authors elaborate what are these aqueous-phase reactions led to the formation of OS? Any other OSs formation pathways?

Line 169, “It is also noted that a BEH170 Amide column was employed to separate the C2-C3 OSs and isoprene OSs in this work. The OS quantification here was more accurate than the study conducted in 2019, in which a reversed-phase column was used to separate the low-molecular- weight and highly polar OSs.” Can the author elaborate this statement? Why the OS quantification is more accurate in this work?

Line 210, “The cruise observations indicated that organosulfate, besides MSA, should be taken into consideration when studying the sulfur cycle and its climate effects in marine atmospheres, especially over regions with high phytoplankton biomass and high temperature.” Can the authors comment what is the contribution of OSs and MSA to the aerosol sulfur in their study? Would the OSs affect the CCN formation in marine boundary layer given the abundance of OSs was comparable to that of MSA in summer?

Line 240, “The low-NO conditions in summer favored the IEPOX formation from isoprene oxidation via HO2 pathway, while the formation of MAE via NO/NO2 pathway would increase under the influence of continental pollutants in autumn and spring (Wang et al., 2020; Worton et al., 2013).” Could the authors comment what is the relative importance of these two pathways based on their measurement data?

Line 284, “Principal Component Analysis (PCA) was performed to further understand the sources of atmospheric OSs over the YBS285 (Fig. 6, Table S2).” This is a nice analysis. As the samples were collected for 10−24 hrs, how the long sampling duration would affect the inputs of the parameters (e.g. the time averaged particulate components concentrations) and interpretation of the results?  Would the variation of the height of boundary layers over the time affect the determination of the concentrations?

In this manuscript, the authors present a thorough study on atmospheric organosulfates (OSs) in the East Asian marginal seas, focusing on seasonal variability, chemical composition, and the impact of biogenic marine emissions and transported anthropogenic pollutants. The study utilizes observational cruises across three seasons (spring, summer, and autumn) and integrates high-resolution chemical analysis, principal component analysis (PCA), and back-trajectory assessments to attribute sources and mechanisms of OSs formation. The authors highlight the underestimated importance of OSs in the oceanic sulfur cycle and their possible role in the climate system alongside traditional species like methanesulfonic acid (MSA). The study is well-structured and results are well discussed. Below are the comments for consideration:

General comments:

The manuscript has a focus comparing OSs levels to MSA, implying both as sulfur-containing organic species and potential CCN. However, they may not necessarily have similar hygroscopicity and CCN activity and therefore climate impact. It is recommended to clarify distinction between MSA and OSs first (regarding precursor, formation pathways and chemical structure), improve transitions between discussing secondary OSs vs MSA, and later on discuss with literature supporting the physicochemical properties of the identified OSs.

The terms “OS” vs “OSs”, “NOS” vs “NOSs”, and “VOC” vs “VOCs” should be used more consistently, e.g., Line 250: “OSs concentrations” vs Line 255: “OS concentrations” vs Line 211: “organosulfate”.

Language editing is needed for some sentences starting with “While…” (Line 35-37, Line 54-57, Line 125-126, Line 236-238).

Specific comments:

Line 43-46: “Another important SOA formation pathway from isoprene and monoterpene oxidation is facilitated by acidic sulfate particles under high humidity conditions, with organosulfates (OSs) as the products (Brüggemann et al., 2020). Sulfate aerosols could be readily formed via DMS oxidation and are generally abundant over various marine environments (Andreae, 1990; Li et al., 2018; Yan et al., 2024).” More story-telling is needed to clarify why DMS-derived sulfate is discussed here with other biogenic OSs. Also consider citing some mechanism-focused studies here to highlight how aqueous-phase chemistry drives reactive uptake of epoxydiols by sulfate aerosols.

Section 2.1: Give a brief introduction about the geographical and climate characteristics of Yellow Sea and Bohai Sea (YBS), and state how the measurement here would address current research gap. It will be good to also mention the time resolutions of filter sampling and other measurements including WS, RH, EC, and Chl-a.

Line 78: The short form for chlorophyll-a (Chl-a) should be denoted here as the first appearance in the manuscript.

Section 2.2: Do the authors also correct for extraction efficiencies and quantification uncertainties? Some quantitative descriptors (e.g. R², S.D., uncertainty range, n-values) can be reported consistently throughout the manuscript.

Line 111: “The OA concentration was then calculated by multiplying OC by 1.6.” Cite the reference for the estimation.

Line 114: “The concentrations of non-sea-salt potassium ion (nss-K+) and non-sea-salt sulfate (nss-SO42-) were calculated by [K+]−0.037×[Na+] and [SO42−]−0.2516×[Na+].” Cite the reference for the estimation.

Line 124: “…under high RH conditions in coastal areas, which favored the aqueous-phase formation of OSs in the atmosphere.” What are the chemical pathways? Cite the references to support the argument.

Line 166: “The IEPOX-OS, a typical low-NO oxidation product of isoprene, was one of the dominant compounds during the summer cruise…” Critical citations on mechanistic and observational studies are needed to support further discussion in this paragraph.

Line 190: “The higher seawater Chlorophyll-a (Chl-a) during summer indicated elevated isoprene production by phytoplankton, and higher temperature favored the sea-to-air transfer process of isoprene (Fig. S3).” It is noted from Fig S3 and S6 that the median do not differ much from other seasons. Please mention the number of measurements and comment on the range of Chl-a measured during summer and whether this elevation is significant.

Line 209: “This suggested that the atmospheric OSs and MSA formation was limited by the same environmental factors in autumn,” Whereas MSA has often served as an indicator for marine biological activity, do the author also have plausible explanations for the weaker correlation during summer?

Section 3.5: Consider reporting how many samples and variables were input into PCA in the maintext.

Line 307: “Elevated OS concentrations were observed as the increasing of air temperature in summer or as the increasing of wind speed in spring (Fig. 7).” Some language editing may benefit, e.g., OSs concentrations elevated with increasing air temperature in summer and increasing wind speed in spring.

Line 327-329: “The results highlight the abundant formation of airborne OSs in summer, which is promoted by the elevated biogenic VOC emissions from surface ocean. During high biological activity periods, atmospheric OS levels could surpass the MSA concentrations in marine aerosols, which is a vital species in the well-known climate regulation via oceanic phytoplankton sulphur emissions (CLAW hypothesis).” For broader implication, the authors may also discuss the potential of different organic sulfur species (particularly MSA vs biogenic like isoprene-derived OSs) as alternative molecular tracers for phytoplankton-derived aerosol, in which the inclusion of these tracers may offer greater sensitivity under certain seasons or atmospheric regimes.