Complex Validation of Weather Research and Forecasting—Chemistry Modelling of Atmospheric CO₂ in the Coastal Cities of the Gulf of Finland

Round 1

Reviewer 1 Report

All the comments are reported on the attachment.

Comments for author File: Comments.pdf

Author Response

Thank you for the review!
Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

General comments

Add line numbers to make the review process much easier.

The description in the introduction and Data and methods is too long, consider to remove some and make it more concise.

The analysis of the results is not promising, too simple. More analysis should be conducted, e.g., wind, CO2 spatial distribution on a map over the study domain. First of all, authors should evaluate the model simulation with observations to make sure that model simulated is reliable, by selecting one case.

What are chemical ICs and BCs for WRF-Chem?  Consider to use CAM-Chem, a global model output.

It has 25 vertical levels which are sufficient to resolve physical processes within boundary layer. It is recommended to have around 60 vertical levels.

The output is every 10 min which is intense. Since the study period is Jan 2019 – Mar 2020, the total amount of data is significant large. I believe hourly output should be sufficient.

Figures and tables:

Figures in this manuscript are very basic. Add more figures along with explanation. In addition, while analyzing a certain panel in a figure, refer to it in the text. For instance, there are 4 panels. Authors could cite panels (c) and (d) while analyzing wind speed.

Figure 2: include terrain height as contours.

Figure 3: The white circle is too small to see it clearly. Consider enlarge the figure or make the circle bigger.

Figure 5: It turns out WRF-Chem intends to overestimate wind speed (c and d). Why?

Figure 7: What is “VMR” in the Y-axis?

Figure 8: The confidence interval is really low < 0.5 ppm. Is it believable?

Specific comments

Abstract

“The accuracy of such models greatly determines errors of the emission estimations.” No information about emission estimations in this study.

2. Data and methods

P3: “The predominant vegetation type near the station is mixed forest”. What is “mixed forest”?

ok

Author Response

Thank you for the review!

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

The accuracy of anthropogenic CO2 emission estimation based on the solution of an inverse problem using accurate measurements of CO2 content and numerical models of atmospheric transport and chemistry is greatly determined by the accuracy of such models. Here, the capability of the model WRF-Chem is validated to simulate atmospheric CO2 emissions on the territories of two large coastal cities of the Gulf of Finland - St Petersburg (Russia) and Helsinki (Finland). Simulations with WRF-Chem can provide annual variations as well as mean seasonal and diurnal cycles of near-surface CO2 mixing ratios in Helsinki on a high spatial resolution (2 km). Correlation between the modelled and measured CO2 mixing ratio is relatively high (~0.73). The errors can be caused by inaccuracies in atmospheric transport modelling and in a priori CO2 emissions and biogenic fluxes. The simulated total atmospheric column (XCO2) in St Petersburg for Jan 2019 - Mar 2020 correlate well (~0.95) with ground-based spectroscopic measurements by IR Fourier-spectrometer Bruker EM27/SUN. Errors of XCO2 modelling are most likely related to inaccuracies in chemical boundary conditions and a priori CO2 anthropogenic emissions. The errors for St Petersburg are ≤0.2% in 60% of cases.

General comments

It is concluded that this methodology to evaluate CO2 anthropogenic emissions of St Petersburg on a city-scale is satisfied.

The paper addresses relevant scientific questions within the scope of the journal.

The paper presents novel concepts, ideas, and tools.

The scientific methods and assumptions are valid and outlined.

The description of experiments and analyses is complete and precise to allow their reproduction by fellow scientists.

The quality and information of the figures and tables are fine.

The title and the abstract reflect the whole content of the paper. It should be mentioned in the abstract that three models are applied for St. Petersburg.

The overall presentation is well structured and clear.

The mathematical symbols, abbreviations, and units are generally correctly defined and used.

Specific Comments

How the vertical profiles of meteorological parameters are measured at Voeikov Main Geophysical Observatory?

Are there any plans to continue the measurements of CO2 TC in St Petersburg?

Technical corrections

A lot of abbreviations are not explained.

Author Response

Thank you for the review!

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

This statement contradicts itself “The modelled profiles of meteorological parameters were linearly interpolated to the vertical resolution of the measurements (up to 50 hPa which is the WRF-Chem approximate upper limit) to compare them”. Before comparing modeled and observed meteorological variables, it's essential to conduct an energy balance to validate these variables.

On the other hand, you said “ CO2 in the atmosphere is considered as fully inert gas”. You must consider CO2 reactions.

The entire manuscript presents considerable complexity in comprehension. For instance “ To use the available observations of CO2 TC in St Petersburg (Peterhof) it can be assumed that CO2 content in an air mass, transporting to St Petersburg, is influenced only by transport from remote territory (for example, from the domain’s boundaries)”. You should enhance the entirety of the manuscript.

What does "GGA" represent in Figure 6 and Table 2?

You said that “In general the model underestimates CO2 mixing ratio relative to the measurements - to 1.5 ppm and less than 1 ppm during night and day hours, respectively”. Could you please provide an explanation for this?

The entire manuscript presents considerable complexity in comprehension. For instance “ To use the available observations of CO2 TC in St Petersburg (Peterhof) it can be assumed that CO2 content in an air mass, transporting to St Petersburg, is influenced only by transport from remote territory (for example, from the domain’s boundaries)”. You should enhance the entirety of the manuscript.

Author Response

Thank you for the review!

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors have responded to my previous comments. No more comments.

Reviewer 4 Report

The manuscript has been enhanced.