the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 06 May 2024
Measurement report: Temporal variability of vertical profiles of CO2 and CH4 over urban environment
Abstract. Understanding the boundary layer dynamics over urban areas is important to improve estimates of the emissions of greenhouse gases (GHG), and predict their atmospheric mole fractions in these areas. Here we present the results of the annual vertical profiling measurement campaign performed in Krakow (Southern Poland). The campaign consisted of 12 monthly-based diurnal measurements of CO2 and CH4 molar fraction vertical profiles supplemented by meteorological parameters focused on the investigation of the dynamics of nocturnal boundary layer vertical structure within the urban boundary layer. The profile data were collected using two platforms: (i) a tethered touristic balloon operating commercially in the city centre and (ii) a drone system, with the selection of the platform based on operational availability and meteorological conditions. CO2 and CH4 molar fractions were measured using Picarro G2311-f (Picarro Inc., Santa Clara, California, USA) cavity ring-down spectrometer, while the meteorological conditions along the profile were measured using a set of temperature, relative humidity, pressure and wind low-cost sensors dedicated for application on-board of UAV platforms. The obtained results allowed us to analyse in-depth the formation, development and disappearance of the nocturnal boundary layer. In selected profiles, a CO2 and CH4 plumes located over the inversion layer (150–250 m AGL) were detected during the nighttime and morning hours. The application of high-resolution numerical simulations using the WRF-GHG model made it possible to identify the source of CO2 plume as a power plant located ca. 10 km southwest of the balloon launch location.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2024-1167', Anonymous Referee #1, 22 Jul 2024
General comments
The paper is a Measurement report on urban vertical profiles of atmospheric CO2 and CH4 in situ measurements. The measurements were collected during 11 intensive period covering days, roughly every month. The platforms used alternate UAV (sampling air directly injected in a Picarro) and touristic tethered balloon. The data is commented through a general overview of the dataset, through examples of daily boundary layer development and its link to vertical profiles of trace gas species, and finally through a case study of the influence of nearby coal plant exploiting high resolution WRF simulation.
The collection of vertical profiles in repeated intensive periods is certainly valuable and such measurements could ultimately contribute to a better quantification of urban emissions.
Here, a few case studies are selected and analyzed. The strategy behind the selection of the case studies is not really explained. The results on BLH development are in essence short pedagogical illustrations of expected atmospheric behavior; they do not bring novel information. The profiles with CO2 enhancements are left half unexplained, even after mobilizing a high-resolution simulation. The couple of CH4 profiles are simply introduced in a figure but no fair analysis is offered.
The shallow and descriptive analysis of the case studies falls short of demonstrating the value of vertical profiles for urban GHG emission research.
Given the lack of novelty extracted from the data reported here, this paper could be reworked to improve the case studies and their interpretation, and to be considered for submission as a dataset description paper than as an ACP measurement report.
Specific comments
L7 Abstract: indicate maximum altitude reached for each platform?
Introduction: I find the introduction theoretical and generic. It could be reinforced on developing a more solid argument for the vertical measurements reported here and lay the ground for the selected case studies (e.G. CO2 point sources in a mixture of urban emissions).
L31 I suggest to replace ‘development’ by ‘validation’.
L31 : ‘and also in the calibration and validation of satellite-borne measurements’ – this is true only for profiles that span full troposphere and lower stratosphere
L34-47 It is not immediately clear what is the point of this paragraph. Please highlight to the reader the relevance of this paragraph
L38 ‘The variability… ‘ - this is relevant for CO2, but other GHG (CH4) deserve a significantly different description.
L50-52: please also include vertical profiles from tall towers, and aircores in the discussion
L55 in this case UAV with discrete sampling should be differentiated from aircore sampling in their ability to achieve detailed vertical resolution
L140 please provide this literature review and the other reason for this choice
L157 the paper should briefly mention how is the WMO calibration scale propagated to the working standards
L159 for the 200 m tubing is a flush pump used or is the Picarro pump sufficient?
L254+ what are the meaningful spatial resolution (if applicable) of land surface databases? Is it relevant and justified to use 200m/1s resolution for the simulation? Given the reason for modelling given at L77 this complex model configuration is maybe an oversize solution?
Figure 2 could be more interesting to replace daily means in panels B by an envelope extending from daytime mean to nighttime means daily values.
Figure 3. Maybe averaged profiles per period of the day and per season could be more explicit?
L292 I would not describe the interpretation of this figure as ‘easily’ identified – given the density of the figure the wording sounds a little bit ironic.
L293 please define SBL determination in this context and describe the data stratification that was performed to arrive at these mean values.
Section 3.2 is interesting as academic illustrations but it is unclear what is the added value of this description. The selected academic examples are not put in the perspective of new information that would be expected from such a paper.
Figure 4 – too many profiles: the visual clutter and the colors make it challenging to follow the interpretation. Given the title of section 3.2.1, why show all day’s measurements? Top row in the figure do not bring information.
L326-327 : are these the only two flights where this enhancement has been observed? Or are they just selected examples? How are they selected? How representative are they?
L345 remind what different tagged tracer were included.
Figure 6 why not also show CH4?
Figure 7 so the likelihood of source receptor relationship is fairly well established for this case, but how useful is it? it would be interesting to show also the simulation using total CO2 emissions next to the power plant tagged tracer
L349 So what may have caused this enhancement, comparable in importance to the other one associated to the power plant? How would that be processed? What other important sources are influencing the measurements in this dataset?
L350-355: is it possible that the choice of 200m spatial resolution is not appropriate or running out of control?
How sensitive is the simulation to injection height? Injection velocity and gas temperature?
L360 could the same information be obtained with a simpler approach?
L364 what is a quasi gaussian plume here?
Fig 8 why not also show CO2 here?
Section 3.3.1: there is no articulated information in this section, I suggest to remove it completely.
L375-378 I find this statement poorly supported by the current text. However I assume that deeper work on the interpretation of the dataset may ultimately support such a finding.
L380-381 Same as above, I find this statement poorly supported by the text.
Conclusion: I suggest to finish the conclusion with some opening toward potential applications and suggestions rather than on an 'impossible' measurement (I agree that reporting negative findings is useful for the community but maybe elsewhere in the conclusion). Maybe further research using different anemometer would solve the problem? or ground based lidar if available?
Editorial
L32 : all ‘these’ components- not ‘the’?
L57ff : this paragraph is challenging to read. I encourage the authors to review the logic, and to simplify with shorter sentences
L361 maybe this section should be numbered 3.4? why is the CH4 case study numbering one level lower than CO2?
Citation: https://doi.org/10.5194/egusphere-2024-1167-RC1 -
RC2: 'Comment on egusphere-2024-1167', Anonymous Referee #2, 24 Jul 2024
The manuscript presents a measurement report on urban vertical profiles of atmospheric CO2 and CH4 using in situ measurements collected over 11 intensive periods. The data collection platforms included UAVs and tethered balloons. The study aims to provide insights into the vertical distribution of these GHGs and explores the influence of boundary layer development and nearby emission sources, which could significantly contribute to the understanding and quantification of urban emissions.
After carefully reading the manuscript and the other reviewers' comments, I agree that this manuscript may need a major revision. For example, the selection strategy for the case studies is not clearly explained. Providing a rationale for choosing specific case studies would help in understanding their relevance and importance. The analysis of boundary layer height (BLH) development is overly simplistic and does not offer new insights into atmospheric behavior. The CO2 profiles with enhancements seem inadequately explained, even with the use of high-resolution simulations. A deeper investigation into these profiles is necessary to elucidate the underlying mechanisms.
Citation: https://doi.org/10.5194/egusphere-2024-1167-RC2
Data sets
Observational datasets of urban CO2 fluxes, atmospheric vertical profiles of CO2 and CH4 and 14CO2, and isotopic composition of atmospheric CO2 at Krakow, Poland; period 2021-2023; part of the CoCO2 project Mirosław Zimnoch, Piotr Sekuła, Alina Jasek-Kamińska, Alicja Skiba, Michał Gałkowski, Łukasz Chmura, Jakub Bartyzel, Paweł Jagoda, Michał Kud, and Jarosław Nęcki https://doi.org/10.18160/8DSK-R4JS
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