Characterization of Imidazole Compounds in Aqueous Secondary Organic Aerosol Generated from Evaporation of Droplets Containing Pyruvaldehyde and Inorganic Ammonium
, Tingting Lu 1, Weixiong Zhao 2, Changjin Hu 2, Xuejun Gu 2 and Weijun Zhang 2,*
Round 1
Reviewer 1 Report
The manuscript by Lin et al. describes an experimental study on the formation of imidazole compounds from pyruvaldehyde and ammonium salt. The study is quite interesting and of importance in the field of SOA chemistry. Several points of suggestions the authors might want to consider are listed below:
- The sources of organic carbon can be discussed in more details related to the current study. For example, are glyoxal, pyruvaldehyde, and related compounds from nature or emitted by human activities? Why focus on imidazole among many other SOA chemicals?
- Line 162, what does "200 single particles are collected" really mean? 200 PM particles or 200 signal points in TOF-MS?
- The evidences for 4-methyl-imidazole and 4-methyl-imidazole-2-carbaldehyde might look strong, but for chemists, they are still circumstantial. The MS only gives you molecular weights, and the UV and IR give you the types of molecules. Can the authors at least speculate on what can be done if the extraction was handled by a careful chemist? More sophisticated separation techniques followed by NMR for example? Theoretical calculation can also help to better decipher the UV and IR spectra.
- The discussion can be shortened somewhat. You probably do not need sentences such as "Ammonium ion has four hydrogen atoms". The English does need to be improved.
Author Response
Dear reviewer,
Our revised manuscript entitled “Characterization of imidazole compounds in aqueous secondary organic aerosol generated from evaporation of droplets containing pyruvaldehyde and inorganic ammonium” by Xin Lin et al. is submitted to Atmosphere for the consideration of publication.
Thank you very much for the suggestions about the further improvement of it. We have carefully considered the comments and revised the manuscript accordingly. The detailed reply to the comments we have made are listed in the attached document.
Best Wishes!
Sincerely Yours
Xin Lin, Mingqiang Huang
Author Response File: 
Author Response.doc
Reviewer 2 Report
This paper investigated the chemical and optical characterization of imidazole compounds in aqueous secondary organic aerosol(aqSOA) generated from reaction of pyruvaldehyde with inorganic ammonium. The imidazole components of aqueous secondary organic aerosol (aqSOA) generated from the reaction of pyruvaldehyde and inorganic ammonium are on-line characterized by aerosol laser time-of- flight mass spectrometer (ALTOFMS) and off-line detected by optical spectrometry in this study. This paper also pay attention to the optical properties (mass absorption coefficient) of the products and the influence of other ionic components (Cl, CO32-, NO3- etc) except for (NH4)2SO4. I think that this topic could be interesting for the readers of atmosphere. I have some comments that I hope can be helpful for the authors to improve the quality of the manuscript.
1.In Section 1 Introduction, The author put forward that previous study do not pay attention to the optical properties of the products from aqueous reaction. However, I think much work concerned optical properties of production from reaction of glyoxal with ammonium sulphate. So, I suggest revise the expression.
2.Add “and” before “the stretching vibration peaks of C-N bond and C=N bond emerged in the infrared spectrum.” in Section “Abstract”.
3. Why select Pyruvaldehyde as precursor? Some description should be added.
4. In Section 2.2, the mixed solution of 5 mM pyruvaldehyde and 10 mM ammonium sulfate reacted each other to form aqSOA? How long will the dark reaction take to form aqSOA? And whether the mass of aqSOA change with reaction time or not? Or you only consider aqSOA from water evaporation? Is it scientific via atomizer? And the title was not proper.
5. In Section 2.2, aqSOA particles are collected by Teflon filter membrane, and extracted into 5 mL 2% methanol water solution for analysis by UV-vis. However, author selected pure methanol as blank reference. It should be replaced by 2% methanol water solution as a reference.
6. Some title was not appropriate, such as 3.2. “off-line characterization and ….”, since the subsequent content include reaction pathway.
7. The solution appear different color under different ions. And author calculated MAC according to formula (2). How to obtain the Cmass (the organic carbon concentration of the extraction solution (g/cm3)), which was key to Figure 9. And do you consider the eliminate errors from several extracted and dissolved steps.
Author Response
Dear reviewer,
Our revised manuscript entitled “Characterization of imidazole compounds in aqueous secondary organic aerosol generated from evaporation of droplets containing pyruvaldehyde and inorganic ammonium” by Xin Lin et al. is submitted to Atmosphere for the consideration of publication.
Thank you very much for the suggestions about the further improvement of it. We have carefully considered the comments and revised the manuscript accordingly. The detailed reply to the comments we have made are listed in the attached document.
Best Wishes!
Sincerely Yours
Xin Lin, Mingqiang Huang
Author Response File: Author Response.doc
Reviewer 3 Report
The study entitled “Characterization of Imidazole Compounds in Aqueous Secondary Organic Aerosol Generated from Reaction of Pyruvaldehyde with Inorganic Ammonium” by Lin et al., adds interesting information on the potential impact of SOA formed from methylglyoxal reaction with ammonium salts. The article deserves publication after the major comments would be addressed.
Why the authors do not choose 4-methyl imidazole to generate characteristic ions and instead have used the imidazole? The imidazole could not be used in this study since the characteristic ion of the products should include a methyl group.
If the product generated in this study is 4-Methyl-1H-imidazole-2-carbaldehyde why do the authors use imidazole-2-carbaldehyde in ALTOFMS characterization? Why the authors do not use the NMR technique to characterize the products formed in the reaction system.
Please explore in detail the MAC results of this study by adding information about comparison with field brown carbon or black carbon studies. Also, compare the results from this study with that of MAC values related to the glyoxal – ammonium research. Please explore the wavelength dependence and the absolute magnitudes of MAC.
This study lacks quantitative investigations and is based mostly on the identification of the products. Please add some quantitative information related to the mechanism presented in figure 8. Please add information about the investigations of the coproducts in the reactions of methylglyoxal with ammonium. Please add evidence of the formation of tetrols, acetic acid, methanol to reduce the speculative degree of the mechanism.
Why there are solutions of 2% methanol in water used in the study. Please explain.
Add a table and more information related to Cmass measurements.
Please discuss the effect of coproducts on the UV spectra shift? Why not use different concentrations to see if the maximum of the UV spectrum does not shift? Please discuss the chromophore effect of the solvent used. The MAC equation is valid only for solutions where dissolution does not change the chemical identity of the chromophores (e.g. solvolysis) . Please prove that does not happen.
Minor comments and corrections:
Could you please explain in detail and add references accordingly in the introduction about the imidazolaldehyde role in the atmosphere as photoinitiator?
Please use in the entire article the SI units and not the agreed units (e.g. do not use psi for pressure)
In the Material section please specify if the reagents used in the study have been further purified or not.
Line 65: replace “condition” with “conditions”.
Lie 72: replace “focuse” by “focus”.
Line 80: there is a strange word “optics of imidazole” used in the sentence. Change to optical properties instead.
Line 84: do not repeat the aqSOA explanation.
Line 91: replace “the useful” with “a useful”.
Line 124: replace “density” with “the density”.
Line 128: replace “Flourier” with “Fourier”.
Line 205: replace “speculate” with “speculated”.
Line 343, 344: solution is neutral....
Line 351: replace “lossing” by “losing”.
Author Response
Dear reviewer,
Our revised manuscript entitled “Characterization of imidazole compounds in aqueous secondary organic aerosol generated from evaporation of droplets containing pyruvaldehyde and inorganic ammonium” by Xin Lin et al. is submitted to Atmosphere for the consideration of publication.
Thank you very much for the suggestions about the further improvement of it. We have carefully considered the comments and revised the manuscript accordingly. The detailed reply to the comments we have made are listed in the attached document.
Best Wishes!
Sincerely Yours
Xin Lin, Mingqiang Huang
Author Response File: Author Response.doc
Round 2
Reviewer 3 Report
After the second review, the article has improved considerably. I consider that the authors have applied all my suggestions and comments accordingly. The article could be published in its present form.
Despite the only report with major corrections against two others with only minor, I consider that the article sounds much better in the new form.
