This study investigates aerosol and cloud condensation nuclei (CCN) properties over the Central and Northern Great Barrier Reef during a 2022 research cruise. It finds that continental air masses increase CCN concentrations despite lower aerosol hygroscopicity, largely due to organic emissions. Precipitation history and aerosol source regions notably influence particle properties. These results are important for assessing Marine Cloud Brightening as a climate intervention to protect the reef. Long-term observations are recommended for a full climatological understanding. Measurement data with analysis presented in this paper is meaningful, and the manuscript and figures supporting the points are sufficient for the publication. However, it would be nice to reflect some of points listed below in the manuscript.  

The measurement report by Horchler et al. is reporting aerosol size distributions and their activation properties over the GBR which is valuable and informing. The level of data analysis is sufficient for measurement report and the report can be published after addressing the comments. I am particularly pleased with the authors effort to deconvolve size distributions and to derive Hopple minimum which is very relevant not only for the context of the report, but to all aerosol community.

There are, however, several issues with the reporting content.

First, Hoppel minimum, which is essentially the boundary between the Aitken and Accumulation modes, should be systematically presented along with derived Dcrit by CCN-SMPS method. The authors may not or cannot go explaining what can be learned from the consistency or inconsistency of the two metrics (due to the lack of chemical composition), but at least present a Table of both for notable size distributions or observed events.

Second, there is an inconsistency throughout the text between the average and the median values. Aerosols distribute by log-normal law and the median would be most appropriate, but for the purposes of comparison (or aiding readers) in the measurement report the authors could present both in all situations, e.g. put either in the brackets next to the other metric. 

Other comments in their sequence.

Line 115. what was the range of RH during the measurements?

Line 125. In-cloud SS was determined by CCN-SMPS method and/or Hoppel minimum. Why there is a mention of ammonium sulphate? Suppl. Figure S4 does not suggest ammonium sulphate composition either, because kappa 0.2-0.3 for MP/CP is not close to ammonium sulphate kappa of 0.55. Please clarify and explain or amend.

Line 134. Surprisingly, aethalometer absorption measurements are absent which are crucial in determining and quantifying anthropogenic pollution, especially when dealing with continental outflow. There could have been some interesting insights into kappa relationship with BC if that was measured. Could the authors tell why such a critical instrument was not deployed?

Figure 3. Hoppel minimum exists in CP as well as long as the Aitken and Accumulation modes can be deconvolved. So the Hoppel minimum is fairly similar in both and should be specified.

Line 237. The authors may find a key study by Ovadnevaite et al. 2017 in Nature explaining and supporting their results for possible liquid-liquid phase separation phenomenon.

Figure 5. What can we learn from the discrepancy of critical diameter determined by CCN-SMPS method and Hoppel minimum (intersection of Aitken and Accumulation modes can be considered as Hoppel minimum if not visually present)? Perhaps the discrepancy tells about the heterogeneity of size dependent chemical composition not accounted for by CCN-SMPS method which assumes it being uniform and internally mixed.