Manuscript entitled “Chemical characterization of organic compounds involved in iodine-initiated new particle formation from coastal macro-algal emission” studied the identity and transformation mechanisms of organic compounds from low-tide macroalgal emission. This manuscript simulates vapor emission oxidation and new particle formation (NPF) experiments of real coastal macroalgae in a bag-reactor. Based on the integrated mass spectrometry measurements, the authors report for the first time a variety of volatile precursors and their oxidation products in the gas and particle phases in such a highly complex system. The results show that organic compounds dominate the growth of new particles induced by iodine species.

This paper falls in an active field of research, and I believe it brings interesting insights to the study of the ongoing laboratory and field researches of coastal I-NPF. The paper could be published in the journal assuming some minor corrections.

1. Page 4 Lines 96-98: What is the proportion of VOCs and O₃ in the VOCs/O₃ flow of the dynamic mode, respectively?
2. Page 4 Lines 98-99: Does the residence time of 67min refer to the sampling time of particulate matter?
3. Page 5 Lines 133-134: How can we see from Figure 2a when O₃ is injected? And when to add light? Why only see the figure of SMPS under static conditions of the ozonolysis experiment.
4. Page 5 Line 157: Please indicate what kind of macroalgae you choose and how to preserve the algae and seawater. And why you choose this type of macroalgae?
5. Page 8 Lines 225-229: Does accretion reactions or dimer formation change particle size? Please describe the accretion reaction in detail.
6. Page 8 Lines 230-232: Why do ESI-Orbitrap MS and FIGAERO-iodide-CIMS use quartz fiber filter and PTFE membrane filter, respectively? Is filter inconsistency the reason why ESI-Orbitrap MS did not measure bimodal distribution?

The authors reported the chemical composition and evolution of volatile precursors emitted from macro-algae and their oxidation products in the gas and particle phase using a suite of mass spectrometers. But it was shallow and simple about the discussion of the transformation mechanisms of organic compound. I recommend that the authors could make more detailed explanations about the results and explore more precise reaction formulas.

Here are some questions about the methods and results in the following.

Method

81: “In the three ozonolysis experiments”

It seems that only one result (without error bar) is shown in this paper. What is about the remaining two experiments?

84: “In an additional OH-enhanced experiment”

The authors conducted this experiment for simulating atmospheric oxidation process, however, you didn’t even give the concentration of additional OH and the limitation of the experimental design compared with the real environment wasn’t discussed.

120: “TI or TOC in the particles was obtained by subtracting the amount on the back filter from that on the front filter”

I am confused about the calculation. As you said that “The front filter of the double filter pack collected the particles, while the back filter placed downstream of the front filter was supposed to adsorb the same amount of volatile species as the front filter”, may I think of it this way: particles in the front filter and volatile species in the back filter. Why the TI in the particle is not the amount on the front filter? Why it needs to subtracting the amount on the back filter?

128: “Only the compounds that existed solely in the front filter or with ion intensity in the front filter higher than that in the back filter by a factor of 3 were regarded as the organic compounds in the particle phase”   

Please cite suitable literature.

Results and discussion

135, 138: “new particles larger than 14 nm were observed only 58 minutes after the injection of ozone flow”, “With a prolonged residential time of 67 min…”

The authors talked about the results after 58 or 67 minutes. But the maximum of axis about the elapsed time in the Figure. 2 was 50.

136: “No particles were formed in the absence of room light or ozone”.

I don’t see the relevant results (table or figure) shown in the paper.

154: “But those small new particles are expected to grow into CCN active sizes, given longer residence time and uptake of more condensing vapors in the atmosphere”. 

Please cite suitable literature.

156: “3.2 Macroalgal emission”

I think it is more suitable to remove this section to the first part of the Results and discussion

187, 188: “IO, IO2 and ClIO could be from the reactions between I, ClI and O3”, “ClNO2 was likely to form upon similar reaction between Cl and NO2 in the bag reactor”

Give the reaction mechanisms or cite literatures.

195: “which is contrary to the observation by HPLC-ICP-MS that total iodine was mostly dominated IO3- peak”

Could the authors explain the contrast?

259: Scheme II

The formulas are too simple to understand the mechanism of particle formation. It might be meaningful to give formulas like Scheme I for several specific species.