Review

The manuscript only has to undergo small changes and improvements before it can be published. The m/s provides a clear overview of the importance of studying aerosol properties in marine environments, highlighting the significance of clean marine sites and the influence of sea salt aerosols. The measurements techniques and methodologies used to collect the aerosol data at Trinidad Head (THD) site, are described in great detail allowing readers to assess the reliability of the findings. The paper includes a detailed discussion on the relationship between meteorological conditions and aerosol characteristics, providing valuable insights into the role of atmospheric transport and meteorology in shaping the aerosol properties investigated at THD site. The seasonal cycles of the major ionic species and aerosol optical properties as well as their diurnal patterns have been adequately described, and the figures are clear and legible.

Minor issues:

I recommend adding a map that includes major cities such as San Francisco, Eugene, and Arcata. Including a map depicting the campaign location will enhance the reader's understanding of the various influences involved, particularly when considering Arcata's apparent influence on the interannual and diurnal variability of several aerosol parameters investigated (e.g., woodburning home heating during winter), as indicated by the results.

Line 199: Remove the second “that”

The manuscript by Boedicker et al. present the seasonal climatology of aerosol chemical and optical properties at the Trinidad Head observatory, California based on a 15-year dataset. It occurs that sea salt is an important source throughout the year, contributing even to PM1 during winter. Major aerosol components exhibit different monthly and diurnal variability, suggesting differences in sources, sinks and transport pathways. Source apportionment analysis shows two main sources throughout the year, namely sea salt and biogenic, with an additional source during winter, which is anthropogenic/combustion. 

The manuscript is well written and easy to follow. I do not see any reason not to move forward with publication after addressing some suggestions.

1) A map indicating the site and neighboring locations would be helpful.

2) Given that the chemical analysis took place during a 4-year period, were there any trends observed for different components? For example, Weber et al. (2016) observed a declining trend in sulfate and ammonium at the southeastern United Stated during the past 15 years. 

3) Some additional information concerning the PMF analysis could be helpful; what was used as an independent variable? PM1 mass? Or just the sum of the derived ion composition analysis?

4) Why do authors consider that all non-sea salt sulfate is of biogenic origin? Can’t it also be from secondary formation of anthropogenic origin? For example Kirpes et al. (2018) find internally mixed secondary sulfate with sea spray aerosol in the marine environment of the Arctic during winter. 

References

Kirpes, R. M., Bondy, A. L., Bonanno, D., Moffet, R. C., Wang, B., Laskin, A., Ault, A. P., and Pratt, K. A.: Secondary sulfate is internally mixed with sea spray aerosol and organic aerosol in the winter Arctic, Atmos. Chem. Phys., 18, 3937–3949, https://doi.org/10.5194/acp-18-3937-2018, 2018.

Weber, R., Guo, H., Russell, A. et al. High aerosol acidity despite declining atmospheric sulfate concentrations over the past 15 years. Nature Geosci 9, 282–285 (2016). https://doi.org/10.1038/ngeo2665