Impacts of the Tree Canopy and Chemical Reactions on the Dispersion of Reactive Pollutants in Street Canyons

Round 1

Reviewer 1 Report

This manuscript presents a numerical modeling approach to better understand the impacts to pollutant concentrations due to flow field modifications of the urban landscape (building locations, street canyons, and tree canopies). A realistic meteorological and air quality scenario is considered, and sensitivity studies through multiple scenarios (noChem, Base, and two tree canopy densities) are conducted and analyzed. This author recommends publication after the revisions and suggestions provided here:

Primary Edits:

The conclusion section (Section 5) could use some further expansion to better provide details of where pollutant concentrations increased and decreased during the sensitivity studies. Suggest removing the bullet point/list format and describing some of the further details in Section 4 instead to describe the primary impacts, such as the increases on the western side of the street canyon and decreases on the eastern side (this info appears ambiguous currently in Lines 319-322).

Detailed Minor Modifications:

1) Lines 40-42: suggest combining sentences to say:

"To understand the flow field and the pollutant concentrations within a canyon, several tools can be utilized including field measurements [8], wind tunnel experiments [1,3,6–10], and 42 computational fluid dynamics (CFD) simulations [1,4–16]."

2) Line 48: "were even compared" to "were compared"

3) Lines 51-54: Perhaps change "Meanwhile" to "However" to indicate that CFD models can also be used to consider the additional effects described in the second sentence.

4) Line 67: Remove "Besides, " and start sentence with "A few investigators"

5) Line 146: Reference number [14] does not match lead author in references.

6) Line 152: "Number of calculation grid points was 358,682, with the size of the finest grid cell being 3.3 m × 3.3 m × 1.0 m."

7) Figures 3 and 5: These figures are quite busy, may want to consider reducing number of time series of pollutants to only show specific pollutants of interest (or alter marking/color designations).

8) Line 237: Remove "Besides, " and start sentence with "The dense tree canopy"

9) Line 276: Remove "Besides, "

10) Line 285: Remove "Besides, "

11) Figure 7: Consider consistent notation with other figures (e.g., "Tree_s and TreeS")

Author Response

Dear Editor and Reviewers,

 

We are deeply grateful to you for carefully reading our manuscript, and for making constructive suggestions. We have revised our manuscript based on your suggestions.

Please note that the following things:

1. We changed the manuscript template according to the request from the journal editor. The revised manuscript was written based on the new template, and the change of template were not tracked (to avoid noisy change log).
2. In the simulation shown in the first manuscript had included a small error. Thus we corrected them, conducted the simulation again, and some figures and body text were corrected according to the change of results. The main findings and conclusion of the study has not been changed. We are so sorry for our error.
3. According to Academic Editor’s suggestion, we added the comparison between the simulation results and observation. In addition, we changed the height at which the simulation results are shown in figures to 3.0 m from the ground, because the height of the observation station is 3.0 m from the ground.

 

Your suggestions and our responses are listed in the attached file.

 

Best regards,

Tomohito Matsuo (Corresponding author)

Author Response File: Author Response.pdf

Reviewer 2 Report

This is a very well written paper on very interesting CFD simulations of the chemical reactions and flow fields in street canyons.

The equations, figures, writing and experiment set-up all appear to be well constructed with rigorous scientific standards.

I only recommend 3 minor revisions for the following points.

1. A paragraph with references in the introduction giving background on the rich history of CFD and LES simulations in terms of spatial distribution would strengthen the paper. To me, the introduction is a little thin in terms of the 20-year history in this area.

2. In the paper, please clarify the new findings from this study that are different than other papers on this topic. There are certainly interesting findings, but the authors could elucidate what is unique about this study better.

3. Please briefly mention why particulate pollution (primary and secondary) is not discussed, and why not and if this could be an area of future research. 

 

 

 

Author Response

Dear Editor and Reviewers,

 

We are deeply grateful to you for carefully reading our manuscript, and for making constructive suggestions. We have revised our manuscript based on your suggestions.

 

Please note that the following things:

1. We changed the manuscript template according to the request from the journal editor. The revised manuscript was written based on the new template, and the change of template were not tracked (to avoid noisy change log).
2. In the simulation shown in the first manuscript had included a small error. Thus we corrected them, conducted the simulation again, and some figures and body text were corrected according to the change of results. The main findings and conclusion of the study has not been changed. We are so sorry for our error.
3. According to Academic Editor’s suggestion, we added the comparison between the simulation results and observation. In addition, we changed the height at which the simulation results are shown in figures to 3.0 m from the ground, because the height of the observation station is 3.0 m from the ground.

 

Your suggestions and our responses are listed in attached file.

We are looking forward to a favorable response.

 

Best regards,

Tomohito Matsuo (Corresponding author)

Author Response File: Author Response.pdf