Please adjust the following sentence in the abstract to make it easier for the reader to follow your thought:
"The particle size distributions provide assessments of < 10 μm and < 2.5 μm dust deposition rates, and it is suggested that these furthermore represent proxies for PM10 (coarse) and PM2.5 (fine) particle size fractions, respectively."
change to
"The particle size distributions provide assessments of < 10 μm and < 2.5 μm dust deposition rates. Since more than xx to yy% of the aerosol compositiion is made up of dust, these epresent proxies for PM10 (coarse) and PM2.5 (fine) particle size fractions, respectively."

You response to the following point from Reviewer 1:
"27. Page 10, AERONET: You should either use the Angstrom exponent to screen out non-dusty days or use SDA coarse mode optical depth."
deserves to be treated in the manuscript. Please incorporate the most relevant part of your answer in the text of the paper.

What the reviewer implies from comment 28
("28. Page 10, Line 26: “dust particles are predominantly from local sources” but in Abstract you wrote “dust deposits along the Red Sea coast are a mixture of dust emission from local soils, and soils imported from distal sources.” This is contradictory.) is that dust particles are most more numerous in source regions than the ones that are transported through medium and long-range transport, please just state this in your sentence.

You could include your answer to the first point raised by reviewer 3 at the end of you introduction. Namely you state that:
"Particle size distribution plots of 12 deposition samples collected monthly at the KAUST campus throughout the 2015 period are added as Appendix A and Supplement C. The mineralogical data are described under paragraph 5.5 and the normative mineralogy calculated from the chemistry in Fig. 11. The chemical data tables are renumbered as Appendix B."
Please contract this formulation and indicate it at the end of your introduction.

You do not clearly jusitfy why you did not use the Angström exponent as 2 reviewers suggested. Could you make an argument about what you would have learned had you done it?

Please write 1 or 2 sentences in the paper to summarize the answer you have to the following point raised by reviewer 3:
"3. One of the main conclusions is that dust in the Red Sea is a mixture of dust from local soils and dust imported from distal sources, which is something that is already well-known; the paper makes no attempt to quantify the respective contributions. An additional concern that I have is the selection of the sites to measure dust deposition. It is not very clear what is the impact of local construction activities. The authors should make a clear statement in that respect.
Authors Response: Source apportionment is considered to be a further step in our research, to be documented in a following paper. As an approximation the sampler with the lowest deposition rate can be considered to have negligible or the least amount of local dust and sea salt. In the months of December 2014, January, April, March, June, July, and December 2015, the deposition rates at the four sites were similar, and considered to have no or negligible amounts of dust from local construction, campus roads, marine salt, or other particulates."

With these changes made, the paper can go into ACP.

Sincerely,

YVes Balkanski