From the journal Environmental Science: Atmospheres Peer review history

24-Sep-2022

Dear Dr Cleary:

Manuscript ID: EA-ART-08-2022-000101
TITLE: Observations of Coastal Dynamics During Lake Breeze at a Shoreline Impacted by High Ozone

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Reviewer 1

Observations of Coastal Dynamics During Lake Breeze at a Shoreline Impacted by High Ozone

This manuscript shows observational results of the lake breeze effects on thermodynamics parameters, winds, and ozone over Lake Michigan using UASs, surface air-quality (AQ) station, and a wind profiler. The subject seems pertinent to the Environment Sciences, Atmosphere, Journal but I do have some serious concerns about the novelty of this study, lack of data quality control, and the interpretation of some results. In the current form, I recommend a major revision.
Major Concerns:
1. Can the authors state why or which aspect of this work is novel? The subject itself, the impact of lake/sea breeze circulation effects on ozone has been published, and the use of UAS platforms is not that new anymore.
2. There is no description of the quality assurance or quality control for the several measurements. The authors should write about it, and how well each data from each platform agree with each other. It seems that Clearly et al., 2022 (C2002), have published some intercomparisons. However, some sentences should be in this manuscript, so the reader knows how good the measurements are. However, C2022 is not complete either. There is no intercomparison study between RAAVEN instruments and instruments from the other platforms (M210 and AQ station), and there is no intercomparison of the IMET’s RH, and pressure sensor with the AQ station. The manuscript and C2002 do not describe the flight pattern for the M210. Was it just up/down flight, or did the drone hover at certain heights (if so, which ones and for how long)? The problem (for me) is that measurements at stack levels will be more accurate, since problems such as instrument response, and accuracy/precision will be mitigated, so in figures 8 and 9, the 50, 100, 150 m levels will be more accurate/precise.
3. Why do the authors assume that all winds from >180 to >90 and <180 will be a lake breeze? The case of 5/24 day demands more proof that it is indeed a lake breeze event. It might be the synoptic conditions are imposing on the surface data, no? The authors might be right, but it is hard to imagine that the lake breeze front reached inland in the morning (according to figure 2). Was the land/lake temperature gradient strong enough to have such circulation at this early time of the day? The same concern is valid for the 3rd case of 5/21, how can you have a lake breeze circulation at night?
4. Figures 8 and 9 (which seem very important) are very hard to see.
a. Why go to 500 m? The drone can only go to 120 m, and it seems that there is no need to show curves above 250 m. The discussion of RB at 300-400 m does not make much sense either…
b. The color code seems to work well for the u-component, but it is very hard to see for the ozone color chart in figures 8 and 9.
c. Looking to figure 6, it seems that the RAAVEN did spirals at a constant level, but in figures 8 and 9, it seems more like a missed approach profile.
d. Why in some plots data are missing? For instance, in figure 4d, the profile of RAAVEN starts at (about) the surface, but in figure 4j only goes to about 50m.
e. I believe the lake breeze front time should be written somewhere, I do not know when exactly the sea breeze arrived at the location in figures 8 and 9. It seems that the lake breeze reaches the M210 at 17:55 UT on 5/22 in figure 8, but according to figure 2, it reaches the AQ location after 12 pm CST (18:00 UT).
f. The surface temperature record in figure 2 (AQ station) does not seem to agree with Figure 8 (both M210 and RAAVEN). One should explain why RAAVEN temperature has a big variation close to the surface, and IF one can compare to the M210 data (see major concern #2 above), how there is a temperature change from < 22 C (at 17:55 UT) to 27 C (at 18:55 UT) to 24 C (at 19:55 UT) to 25 C (at 20;25 UTC)– probably within the lake breeze environmental conditions according to figure 2.
5. Certain parts of section 3 are hard to read. There are some misspellings (will-mixed), ideas not well explained (see minor concerns), and in general, the whole section should be reviewed.
6. In section 3.4, the authors claim some general patterns for this site. Not sure, if one can make such generalizations based on 1 or 2 cases and such a short time.
7. Figure 10: I do not see how the authors can affirm that there is an ozone maximum at 60 m (or any local maxima) based on their data. I do not see it in figure 9 – which is the only one that has overland and overwater ozone profiles (even in figures 9d and 9g as written in the text).
8. Did the authors analyze the Lidar signal-to-noise ratio to estimate turbulent properties? Hence an independent determination of stable, turbulent, well-mixed layers, and planetary boundary layer heights can be determined and compared.

Minor Concerns (I do have more, but these are the most pressing):
1. I suggest including a brief description of the climatological patterns of the wind direction and even a description of changes in wind flow due to synoptic systems (e.g., cold fronts).
2. In section 3.3 last paragraph, about the discussion about an LLJ/IBL. I believe the paragraph should be reworked:
a. I suggest adding “(fig. 9)” at the end of the 1st sentence.
b. “By the afternoon, the breakup of the strong morning inversion was more advanced over land than the water profiles, leading to higher ℎ ― 2. Below ℎ ― 2, the land RB profiles showed well-mixed conditions; unlike the water profiles, which remained stable right down to the surface”. This is a confusing sentence. What is the “strong morning inversion”? Is that inversion at 100-200 m at 14:30 UT? “
c. These corresponded to slightly elevated low-level jets (where low shear increased RB) observed in land compared to water profiles. Both the well-mixed surface conditions and the increasing height of the low-level jet over land, suggest the formation of an internal boundary layer (IBL) over the land of roughly 50 – 120 m AGL that the lake breeze ramps over when it reaches the shoreline.” First, RB increases due to low shear and/or high potential temperature gradients as shown in Figures 8 and 9. Also, the second sentence is confusing. Why do well-mixed surface conditions and increasing height LLJ lead to the formation of the IBL? I thought that the IBL will be formed due to the lake breeze circulation. Also, from my understanding, the presence of a well-mixed layer below goes against the formation of LLJ. I do not quite understand this sentence “the lake breeze ramps over when it reaches the shoreline”… are the authors implying that lake breeze air-mass (colder) goes over the terrestrial air-mass (warmer)?
d. Did the authors observe any LLJ? I did not see any wind speed profile in the manuscript, and it is very hard to see any jet in the vector plots in Figures 8 and
3. About the LCL discussion (last paragraph of section 3.4), which LCL the authors are discussing? From the water or from the land? After the lake breeze front or just in general? What time of the day you will have such LCLs, I suppose the authors are discussing the land LCL (probably from the AQ station) and its daily maximum value. If so, why this is pertinent to this study? I believe this study is trying to infer the IBL induced by the lake breeze circulation, no? It would be more interesting to show the LCL during the lake breeze events and its differences from the non-lake breeze conditions. By the way, you do not need “well mixed conditions” to calculate the LCL (“Using surface relative humidity measurements during well mixed conditions we were able to estimate the height of the lifting condensation level (LCL)”.
4. Some figures are in CST and others are in UTC. Please, be consistent and use only one standard.

Reviewer 2

General comments
It is a good research angle to focus on the effect of lake breeze circulation on ozone and start from the vertical profile of ozone. However, the results of the study rely on only 6 days of observations, and the limitation of this research should be declared. The article has the following problems that need to be improved. Other suggestions for improvement are listed below. To sum up, I recommend accepting it after careful revision.
Specific comments
1) How to exclude the influence of aircraft exhaust emissions on the observation results?
2) How efficient is the UAS system?
3) How is time stamp formed?
4) What is the flight path of the M210?
5) What is the principle of POM measuring ozone?
6) Ozone concentrations have already peaked when some lake breeze appear, and combined with changes in NOx concentration, it is more likely to be the effect of local emissions than lake breeze. I don't think there were 5 times more lake breeze that caused the ozone to rise. This part needs to be combined with the discussion of vertical profile changes to prove that horizontal transport does occur. It is suggested that the authors can distinguish events in which ozone is affected by lake breeze by color.
7) The content of section 3.2 is not clear enough. It is recommended to discuss which wind direction causes ozone to rise and whether there is an emission source in this direction. Events with large ozone changes, such as 21(1) and 22, should be focused on.
8) What specific and obvious differences are not mentioned in Section 3.3 before and after the appearance of wind? The boundary layer and turbulence will change regularly with the sunset. It's hard to tell with just two days of data how much lake wind played a role.
9) High concentrations of ozone could come from the residual layer. However, the residual layer usually disappears in the early morning and after sunrise. The residual layer usually does not appear at the time points of Figures 8ab and 9bc. Assuming that there is a residual layer, it is reasonable that there should be a high concentration of ozone on the profile in Fig. 9a. I doubt this statement.
10) Is the highest concentration at 100 m related to ships at lake rather than lake breeze?
11) The results of the article is not clear. Whether the high ozone concentration is the result of local emission or transport by lake breeze?
12) The sea breeze is mentioned many times, which is easy to confuse the readers. Can sea breeze and lake breeze be generalized?
Technical comments
1) Figure 4. Wind direction is suggested to be changed to vector.
2) There are too many pictures in the article. It's better to put some less important ones in attachments.
3) What is the area of the lake? Are there any pollution sources such as boats on the lake?

Comments to the Author
Observations of Coastal Dynamics During Lake Breeze at a Shoreline Impacted by High Ozone

This manuscript shows observational results of the lake breeze effects on thermodynamics parameters, winds, and ozone over Lake Michigan using UASs, surface air-quality (AQ) station, and a wind profiler. The subject seems pertinent to the Environment Sciences, Atmosphere, Journal but I do have some serious concerns about the novelty of this study, lack of data quality control, and the interpretation of some results. In the current form, I recommend a major revision.
Thank you for your thorough review of this manuscript.
Major Concerns:
1. Can the authors state why or which aspect of this work is novel? The subject itself, the impact of lake/sea breeze circulation effects on ozone has been published, and the use of UAS platforms is not that new anymore.
While there are ground observations of lake/sea breeze effects on localized coastal pollution, vertical profiles of lake breeze can be obtained through remote sensing (LIDAR) which has a dead zone up to 100 m AGL to extract wind profiles. Flying UAS into the low altitude space of inversion allows for a targeted exploration of the lower atmosphere in a dynamic coastal environment, capable also of measuring in situ ozone observations and meteorological parameters like relative humidity and temperatures in addition to wind profiling. This allows for a more thorough representation of the atmosphere than one remote sensing device alone, and with more coverage of the lower atmosphere than by LIDAR or by manned aircraft which do not remain at low altitudes for a significant amount of time (nor do sonde observations monitor near-surface observations for any long duration). This manuscript was solicited as a part of a UAS in Atmospheric Sciences Special Issue, so we feel that it highlights the use of UAS in an environment which has phenomenon on the scale of routine UAS observations that are meaningful to pollution dispersion. Language has been added to the Introduction to address these concerns.
“During the 2017 Lake Michigan Ozone Study, manned aircraft overwater flights observed high ozone within the lowest 100 m above lake level, which is a domain more safely sampled by UAS for a longer duration.” Has been added to the introduction to indicate the novel domain this sampling strategy investigates.
2. There is no description of the quality assurance or quality control for the several measurements. The authors should write about it, and how well each data from each platform agree with each other. It seems that Clearly et al., 2022 (C2002), have published some intercomparisons. However, some sentences should be in this manuscript, so the reader knows how good the measurements are. However, C2022 is not complete either. There is no intercomparison study between RAAVEN instruments and instruments from the other platforms (M210 and AQ station), and there is no intercomparison of the IMET’s RH, and pressure sensor with the AQ station. The manuscript and C2002 do not describe the flight pattern for the M210. Was it just up/down flight, or did the drone hover at certain heights (if so, which ones and for how long)? The problem (for me) is that measurements at stack levels will be more accurate, since problems such as instrument response, and accuracy/precision will be mitigated, so in figures 8 and 9, the 50, 100, 150 m levels will be more accurate/precise.
The revised manuscript includes an intercomparison between the RAAVEN and M210 observations and AQ station in the SI: Figures S7 and S8. The M210 made geostationary flights (just up and down) and this has been described in the methods section. The performance of the Personal Ozone Monitor tends to improve with very slow ascents, capturing fresh air samples that are considered undisturbed by prop wash during the ascent and the ascent data was used for analysis. In order to capture the vertical profile of the atmosphere at a time when the atmospheric conditions are changing over time, the data from rapid descents or ascents were used to capture the vertical profile within a smaller time window. The step-wise data captured during ascents or descents with the RAAVEN occur over a longer time-span of 1 hour, whereas the atmosphere is changing faster, thus making the improved statistics per altitude relevant only to those time windows at specific altitudes, but does not provide a static view of the vertical profile over that span of 1 hour due to the changing atmospheric state.
Language to address this has been added to the discussion of Figures 8 and 9.
3. Why do the authors assume that all winds from >180 to >90 and <180 will be a lake breeze? The case of 5/24 day demands more proof that it is indeed a lake breeze event. It might be the synoptic conditions are imposing on the surface data, no?
There is always a synoptic influence on marine air incursion at this location, wherein if the synoptic winds are too strong from the west, the lake breeze circulation will not occur (Laird et al 2001). It is clear from the wind fields that the easterly component of u winds on May 24 is not sustained to high altitudes and opposes a westerly flow aloft.
The language in the document has now highlighted the change in wind direction, drop in wind speed and drop in temperature to all indicate the incursion of marine air. The example of this being a front is May 23 when cold air was sustained all day from the north. A lake breeze did not emerge on the 24th but the site was characterized by low-level easterly winds that opposed westerly at higher altitudes. Satellite observations have also been used to identify cloud suppression around the lake during times we did measurements (See SI figures).
The authors might be right, but it is hard to imagine that the lake breeze front reached inland in the morning (according to figure 2). Was the land/lake temperature gradient strong enough to have such circulation at this early time of the day?
On 5/24 synoptic winds were influencing the circulation of marine air over land, as usually dominant synoptic flow from south to north or from east to west allows for a wider expansion of marine-influenced air over land. This is addressed now in the document.
The same concern is valid for the 3rd case of 5/21, how can you have a lake breeze circulation at night?
It is driven by differential pressures overland and overwater, with weakening wind speeds that oppose the lake breeze circulation. If there remains surface temperature (and therefore surface pressure) differential when winds die down in the evening, an onset can still occur.
4. Figures 8 and 9 (which seem very important) are very hard to see.
Modifications have been made to these figures to improve clarity
a. Why go to 500 m?
The RAAVEN fixed wing UAS flew to 500 m. What you are seeing in these graphs are real-time observations up to 500 m for the RAAVEN flights and up to 120 m for the M210.
The drone can only go to 120 m (The M210 only flew to 120 m), and it seems that there is no need to show curves above 250 m. The discussion of RB at 300-400 m does not make much sense either…
We have added language to discuss why the Richardson number exploration is important to map out the connection between buoyancy and wind profile observations up to the top of the circulation pattern of negative u winds closer to 500 m AGL.
b. The color code seems to work well for the u-component, but it is very hard to see for the ozone color chart in figures 8 and 9.
The figure has been edited for clarity.
c. Looking to figure 6, it seems that the RAAVEN did spirals at a constant level, but in figures 8 and 9, it seems more like a missed approach profile.
The chosen profiles in Figures 8 and 9 are the full ascent or descent profiles, as can be seen in portions of the flight in Figure 6. We chose the full ascent or descent profiles to show a vertical profile sampled within a smaller time window than when the RAAVEN followed a circular pattern at a given height.
d. Why in some plots data are missing? For instance, in figure 4d, the profile of RAAVEN starts at (about) the surface, but in figure 4j only goes to about 50m.
Some profiles were completed before the RAAVEN landed and so we have data down to the surface, or the profile was completed after the last circle at 50 m AGL and then the RAAVEN rose to 500 m AGL to start another step-down process. The RAAVEN was in the air for 2 hours at a time and did not always land after being at 50 m AGL.
e. I believe the lake breeze front time should be written somewhere, I do not know when exactly the sea breeze arrived at the location in figures 8 and 9. It seems that the lake breeze reaches the M210 at 17:55 UT on 5/22 in figure 8, but according to figure 2, it reaches the AQ location after 12 pm CST (18:00 UT).
A table has been added to the SI that identifies the rapid change to easterly winds as observed at the Ground Station. Because the Ground Station was separated in space from the M210 and the RAAVEN, the time that the lake breeze was captured may not have always been the same by each platform, particularly when the RAAVEN was in Flight Pattern A farther inland.
f. The surface temperature record in figure 2 (AQ station) does not seem to agree with Figure 8 (both M210 and RAAVEN). One should explain why RAAVEN temperature has a big variation close to the surface, and IF one can compare to the M210 data (see major concern #2 above), how there is a temperature change from < 22 C (at 17:55 UT) to 27 C (at 18:55 UT) to 24 C (at 19:55 UT) to 25 C (at 20;25 UTC)– probably within the lake breeze environmental conditions according to figure 2.
The air quality station appears to agree with the observations at the lowest altitudes. Comparisons with ground station data have been included in an SI, noting that ground observations are most likely to be similar to UAS observations at the lowest altitudes.
5. Certain parts of section 3 are hard to read. There are some misspellings (will-mixed), ideas not well explained (see minor concerns), and in general, the whole section should be reviewed.
The section has been edited with added language for clarity.
6. In section 3.4, the authors claim some general patterns for this site. Not sure, if one can make such generalizations based on 1 or 2 cases and such a short time.
The interpretation of the data is clarified to describe what was observed on high ozone days from the campaign May 22 and May 24. Studies of air quality tend to focus on episodic observations due to the episodic nature of ozone exceedances. Some description of the success of this strategy has been described.
7. Figure 10: I do not see how the authors can affirm that there is an ozone maximum at 60 m (or any local maxima) based on their data. I do not see it in figure 9 – which is the only one that has overland and overwater ozone profiles (even in figures 9d and 9g as written in the text).
Figure 10 has been removed.
8. Did the authors analyze the Lidar signal-to-noise ratio to estimate turbulent properties? Hence an independent determination of stable, turbulent, well-mixed layers, and planetary boundary layer heights can be determined and compared.
This is a great idea for more analysis with the Lidar data, which could in its entirety be another publication. As this article is aimed at a special issue with regards to UAS in Atmospheric science, we think the outlined above analysis is outside the scope of this paper.

Minor Concerns (I do have more, but these are the most pressing):
1. I suggest including a brief description of the climatological patterns of the wind direction and even a description of changes in wind flow due to synoptic systems (e.g., cold fronts).
See section 3.1
2. In section 3.3 (now 3.4) last paragraph, about the discussion about an LLJ/IBL. I believe the paragraph should be reworked:
a. I suggest adding “(fig. 9)” at the end of the 1st sentence.
So added
b. “By the afternoon, the breakup of the strong morning inversion was more advanced over land than the water profiles, leading to higher ℎ ― 2. Below ℎ ― 2, the land RB profiles showed well-mixed conditions; unlike the water profiles, which remained stable right down to the surface”. This is a confusing sentence. What is the “strong morning inversion”? Is that inversion at 100-200 m at 14:30 UT? “
The language has been changed to addressed specific changes to the inversion height over the course of the day and differences observed over water and land in the afternoon.
c. These corresponded to slightly elevated low-level jets (where low shear increased RB) observed in land compared to water profiles. Both the well-mixed surface conditions and the increasing height of the low-level jet over land, suggest the formation of an internal boundary layer (IBL) over the land of roughly 50 – 120 m AGL that the lake breeze ramps over when it reaches the shoreline.” First, RB increases due to low shear and/or high potential temperature gradients as shown in Figures 8 and 9. Also, the second sentence is confusing. Why do well-mixed surface conditions and increasing height LLJ lead to the formation of the IBL?
We are arguing that we are observing an IBL over land and not over water due to the well-mixed surface conditions within the lowest 100 m. The cause of the IBL is likely due to conductive heating of the lowest altitude air mass from contact with the land surfaces. The low-level jets could be indications of lake breeze circulation and the IBL is a secondary feature of a marine layer incursion over land.
I thought that the IBL will be formed due to the lake breeze circulation. We agree.
Also, from my understanding, the presence of a well-mixed layer below goes against the formation of LLJ. We agree this is a weird structure.
I do not quite understand this sentence “the lake breeze ramps over when it reaches the shoreline”… are the authors implying that lake breeze air-mass (colder) goes over the terrestrial air-mass (warmer)?
Good point. What we are saying is that the vertical structure of conductive cooling of the atmosphere over water changes to conductive heating over land providing an underlying buoyant, turbulent internal boundary layer, which appears to offset the height of maximum inversion overland. The overall lake breeze circulation and marine air incursion is applicable to the full vertical profile during a lake breeze event. However, a complicated regime of conductive heating, friction from contact with the surface and turbulence slows down flow and increases mixing in the lowest 50-100 m AGL during the lake breeze circulation, and higher level jets may show the overall directional circulation of the lake breeze driven at a higher altitude than directly at the surface.
d. Did the authors observe any LLJ? I did not see any wind speed profile in the manuscript, and it is very hard to see any jet in the vector plots in Figures 8 and 9.
The wind speeds are indicated by the length of the arrows in figures 6 a-f and 7 a-f. In Figures 6 a-f, 6d shows the strongest wind speeds nearer to the surface within the inversion. In figures 7a-f, the strongest winds that are within the lake breeze circulation pattern are from 100-300 m AGL in figures 9e-h.

3. About the LCL discussion (last paragraph of section 3.4 (now 3.5)), which LCL the authors are discussing? From the water or from the land? After the lake breeze front or just in general? What time of the day you will have such LCLs, I suppose the authors are discussing the land LCL (probably from the AQ station) and its daily maximum value. If so, why this is pertinent to this study? I believe this study is trying to infer the IBL induced by the lake breeze circulation, no? It would be more interesting to show the LCL during the lake breeze events and its differences from the non-lake breeze conditions. By the way, you do not need “well mixed conditions” to calculate the LCL (“Using surface relative humidity measurements during well mixed conditions we were able to estimate the height of the lifting condensation level (LCL)”.
We have added analysis under stable conditions to this section and described how the analysis was done (using the RAAVEN UAS platform data overland and overwater). A figure of the LCL heights is in the Supplemental Information document. The reason to include the LCL height calculations in this paper is to demonstrate how UAS were used to describe the thermodynamic state of the atmosphere during the week of observations and how the dimensions of the lake breeze and internal boundary layer are much lower in altitude than LCL.
4. Some figures are in CST and others are in UTC. Please, be consistent and use only one standard.
We converted all the figures to CST.

Referee: 2

Comments to the Author
General comments
It is a good research angle to focus on the effect of lake breeze circulation on ozone and start from the vertical profile of ozone. However, the results of the study rely on only 6 days of observations, and the limitation of this research should be declared.
Such declaration has been added the introduction.
The article has the following problems that need to be improved. Other suggestions for improvement are listed below. To sum up, I recommend accepting it after careful revision.
We thank you for your thoughtful comments.
Specific comments
1) How to exclude the influence of aircraft exhaust emissions on the observation results?
All UAS were battery operated with no exhaust emissions.
2) How efficient is the UAS system?
The maximum flight time for the M210 was 25 minutes and we tried to fly only 15-20 minutes. The maximum flight time for the RAAVEN was 2 hours and low battery power would dictate flight times.
3) How is time stamp formed?
For the M210 and all equipment on it, each dataset (flight log with GPS, iMET and POM) had a digital timestamp. The flightlog and iMET both had satellite GPS information for all flights and the timestamp was uniform. The POM internal clock had to be reset regularly as the satellite GPS was not reliable. The time drift of the POM was as much as 30s per flight, so a longer time-average was used to align the POM data with the iMET and GPS data. RAAVEN instrumentation is all live-streamed to the ground station with the same time-stamp.
4) What is the flight path of the M210?
Vertical ascent and descent. Language was added to the slow ascent description to include a fixed launch point.
5) What is the principle of POM measuring ozone?
“measured O3 using uv absorption with an in-series active subtraction for water vapor interference at a 10 s duty cycle. “ has been added
6) Ozone concentrations have already peaked when some lake breeze appear, and combined with changes in NOx concentration, it is more likely to be the effect of local emissions than lake breeze. I don't think there were 5 times more lake breeze that caused the ozone to rise. This part needs to be combined with the discussion of vertical profile changes to prove that horizontal transport does occur. It is suggested that the authors can distinguish events in which ozone is affected by lake breeze by color.
We think this comment is in reference to figure 4, which is an overlap of ground observations at the onset of lake breeze from Figure 2 and 3. Looking at Figure 3, the ozone concentrations are highest during lake breeze (or easterly winds), particularly on May 22 and 24. On May 22, there is a direct jump in ozone concentrations upon lake breeze onset, whereas during the long sustained period of onshore breeze on May 24, this followed a northern wind and front movement which likely diluted the urban plume that tends to be a reservoir for Chicago and Milwaukee emissions. The increase in ozone in the later day on May 24 appears to demonstrate a plume arrival. The local emissions in this area are small in comparison to shoreline cities like Chicago and Milwaukee, emissions of which both contribute to shoreline ozone along the shoreline of Lake Michigan in both Michigan and Wisconsin (CITATIONS). The lake breeze onset can contribute to limiting ozone extent if the marine layer is cleaner than the overland air masses (which can happen when Chicago plume has a northwesterly flow in the morning instead of an easterly flow over the lake).


7) The content of section 3.2 is not clear enough. It is recommended to discuss which wind direction causes ozone to rise and whether there is an emission source in this direction. Events with large ozone changes, such as 21(1) and 22, should be focused on.
Discussions arising from ground observations has been placed into Section 3.2 (previously Section 3.1) as the analysis arises from the same data that was in Figures 2 and 3 with highlighted analysis from Lake Breeze onset.

The over water marine layer tends to act as a reservoir for emissions from Chicago and Milwaukee as the stratification of the marine layer prevents dilution of emissions into the greater troposphere. This understanding is well documented in analysis from 1973 onward (leons and Cole, Lennartson and Schwartz, Foley, Dye, Cleary, Vermeuel, Stanier).
8) What specific and obvious differences are not mentioned in Section 3.3 before and after the appearance of wind? The boundary layer and turbulence will change regularly with the sunset. It's hard to tell with just two days of data how much lake wind played a role.
All UAS data were collected in daylight hours. A comment has been added to the introduction as to the limited scope of the field campaign to address the concerns of the lack of temporal coverage. We do stress that these experiments were conducted during high ozone episodes which are, by their nature, episodic and which tend not to be modeled well at shoreline locations, thus necessitating increased coverage of measurement strategies.
9) High concentrations of ozone could come from the residual layer. However, the residual layer usually disappears in the early morning and after sunrise. The residual layer usually does not appear at the time points of Figures 8ab and 9bc. Assuming that there is a residual layer, it is reasonable that there should be a high concentration of ozone on the profile in Fig. 9a. I doubt this statement.
The complication at this site is that a residual layer is a layer of stability from overnight temperatures and on May 24 whatever residual layer at this site may have not shown a distinct transition to lake breeze flow as the marine layer inversion was observed from the morning hours onward. The synoptic winds were southeasterly overnight on this day, so whatever was residual versus marine cannot be distinguished. This has been changed in the document.
10) Is the highest concentration at 100 m related to ships at lake rather than lake breeze?
Ships on the lake could possibly contribute to small injections of fresh Nox into the marine layer, but the denisity of ship traffic is much lower than the density of car, truck, heavy-diesel and rail traffic on land in the Gary-Chicago-Milwaukee urban corridor.
11) The results of the article is not clear. Whether the high ozone concentration is the result of local emission or transport by lake breeze?
The marine layer is a reservoir for regional emissions if they are transported overwater, or emitted within the inverted marine layer. This is the main cause of poor air quality along all shoreline locations of Lake Michigan. The most significant sources of ozone precursor emissions are within the Gary-Chicago-Milwaukee urban areas.
12) The sea breeze is mentioned many times, which is easy to confuse the readers. Can sea breeze and lake breeze be generalized?
The complications here are that at specific locations, the effect of this type of circulation arises from the body of water nearby – so this phenomenon on an ocean coast would be a sea breeze and nearer to a large lake is a lake breeze. That terminology is well-established, although we have attempted here to also use terminology for a marine layer incursion as a more neutral generalized term. A sea breeze could possibly have different dimensions than a lake breeze depending on the total thermal differences overwater and overland.
Technical comments
1) Figure 4. Wind direction is suggested to be changed to vector.
Figure 4 has been placed into the SI.
2) There are too many pictures in the article. It's better to put some less important ones in attachments.
The following graphics were placed into the SI:
3) What is the area of the lake? Are there any pollution sources such as boats on the lake?
Lake Michigan is 22406 square miles (58,030 km2). There is some industrical and recreational ship traffic on the lake, but the emissions from these activities is smaller than the large city of Chicago.

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Referee #3
P2. Para 2. Saskatchewan?
So corrected
P2. Para 2. Introduce acronym for internal boundary layer (IBL) here.
So added
P2. Para 3. Add a reference to the OWLETS campaigns which also used UAVs to measure O3 above water.
Sullivan, J. T., et al. (2019), The Ozone Water-Land Environmental Transition Study: An Innovative Strategy for Understanding Chesapeake Bay Pollution Events, Bulletin of the American Meteorological Society, 100(2), 291-306, doi:10.1175/Bams-D-18-0025.1.
So added
P2. Fig. 1. The captions read RAVEN instead of RAAVEN.
So changed
P3. Para 1. Previous studies have shown the POMS to be sensitive to temperature variations created by the thermal profile. This is probably not a problem here since the measurements are only used semi-quantitatively, but the reliability of the measurements should at least be acknowledged.
Li, X. B., Z. R. Peng, Q. C. Lu, D. F. Wang, X. M. Hu, D. S. Wang, B. Li, Q. Y. Fu, G. L. Xiu, and H. D. He (2020), Evaluation of unmanned aerial system in measuring lower tropospheric ozone and fine aerosol particles using portable monitors, Atmospheric Environment, 222, doi:ARTN 11713410.1016/j.atmosenv.2019.117134.
So added
P3. Para 4. I believe the author meant “criterion”. A “criterium” is a bicycle race.
So changed
P4, Fig. 2+. The paper alternates between local time (CST) and UTC in the figures and discussion which is confusing to the reader. I would suggest that all of the figures be standardized to local time since the phenomena discussed here are diurnal in nature.
Figures have been changed to use CST
P4. Sect 3.2. The text begins discussions of the temperature structure aloft here, but does not call out the relevant figures until much later. This and some of the other sections read as if they were written by different authors which makes the text somewhat disjointed and introduces some unnecessary repetition.
P5. Fig 4. I found this figure to be confusing and not particularly useful. If you want to keep it, I suggest showing only the measurements from May 22 and 24 since the rest of the discussion focuses on those two days.
Figure 4 has been placed in the supplemental info. The data from figures 2 and 3 can be used to describe the observations of lake breeze.
P5. Para 1. Please add May 22 Doppler measurements referred to here. See next comment.
Permission was requested from a previous publication (Cleary et al 2022 ESSD) to include here for the May 22 doppler measurements.
P6. Figures. I would suggest merging the plots in Figs. 5 and 6 into one figure with two panels ((a) and (b)) and adding a second panel with the May 22 Doppler measurements to Fig. 7.
So added
P6. Fig 6. The caption for Fig. 6 lists the wrong date.
So corrected
P9, para 4. Change “Overwater” and “overland” to “over water” and “over land”
So corrected
P10, para 1. The LCL estimates are significantly higher than those derived from the nearest radiosondes, Green Bay (≈200 km N) and White Lake (≈350 km E). If anything, I would have expected them to be lower. Could the authors please comment on this?
The LCL estimates were close to those from nearby radiosondes. The LCLs were calculated throughout all measurement days, before and after lake breeze fronts. They were calculated over water and over land. The LCLs did not appear different from over water to over land.

29-Dec-2022

Dear Dr Cleary:

Manuscript ID: EA-ART-08-2022-000101.R1
TITLE: Observations of Coastal Dynamics During Lake Breeze at a Shoreline Impacted by High Ozone

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Reviewer 2

The article is acceptable