Quantifying the Impact of the COVID-19 Pandemic Restrictions on CO, CO2, and CH4 in Downtown Toronto Using Open-Path Fourier Transform Spectroscopy
, Brendan Byrne 2, Orfeo Colebatch 1, Richard L. Mittermeier 3, Felix Vogel 4 and Kimberly Strong 1
Round 1
Reviewer 1 Report
The work is very interesting and well structured. I suggest these minimal changes:
- Prepare a workflow that describes the methodological approach adopted
- Cirate these jobs
Marinello et al., 2021 - How changes in human activities during the lockdown impacted air quality parameters: A review https://doi.org/10.1002/ep.13672
Marinello et al., 2021 - The Impact of the COVID-19 Emergency on Local Vehicular Traffic and Its Consequences for the Environment: The Case of the City of Reggio Emilia (Italy) https://doi.org/10.3390/su13010118
- the captions to the figures are very long. It would be better to include the description of the figures in the text of the paper
- improve the description of the future implications of the work and the results obtained
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Overall, I believe that this is sound original content worthy of publication. It is a good use/synthesis of existing infrastructure/data collection tools to provide new insight in to a very complex topic, the impact of human behavior/vehicular use to the carbon footprint in complex urban environment. My major criticism is three fold, 1) the assessment of solar radiation and temperature as a possible drive for observed changes is provided but not well addressed. This is a complex environment. For example the observed differences in temperature and trends in radiation may be in part be an indicator of cloud cover and PBL height, which could drive concentrations in a quasi closed environments due urban terrain. Some additional short text on why these variables were selected, and what the expected outcome from a concentration perspective might be could add to the readers understanding of the problem. 2) A shift in peak traffic count is observed, but not explained. I fully understand that there may be no data to explain it, or the fidelity in the data is not present, i.e. it could be due to the fact that this peak represent some form of commercial traffic that remained unchanged during stay-at-home periods, but is normally masked by the commuter population. I think some statement about/description of the traffic count data and its limitations might be appropriate. 3) It might be nice to describe/justify possible impact on correlation/de-correlation between traffic sites/their topography and the campus location of the FTIR which seems to has significant green space, and at some distance from one another. In future studies it might be worth considering collocation the traffic count with the concentration observations to get a better direct assessment of the impact of fossil fuel based traffic on GHG concentrations on highly localize urban areas as well as the overall urban canopy. I fully recognize that colocation of such systems often presents a number of challenges. I have put some specific style/grammar/ suggestions/comments in the attached PDF in an attempt to aid the review process
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
The article” Quantifying the impact of the COVID-19 pandemic restrictions on CO, CO2, and CH4 in downtown Toronto using open-path Fourier transform spectroscopy” intends to quantify the changes in mole fractions and enhancements of CO, CO2, and CH4 in downtown Toronto during the COVID-19 stay-at-home periods in (March to May) 2020 and (January to March) 2021, and to determine whether this system could detect the impact of changes in urban traffic emissions on CO, CO2, and CH4.
The study analyses the reduction of surface CO, CO2, and CH4 mole fractions during the stay-at-home periods in downtown Toronto, Canada, having as reference the period before the 2020 restrictions started (2018 and 2019). OP-FTIR system was used to obtain measurements and the meteorology (wind speed, temperature and solar radiation measured) were examined to evaluate the possible influence in gases changes. In addition to measurements the sources of data contain information from City of Toronto Transportation Services, Canada’s Air Pollutant Emission Inventory 2018, Scholars Portal Dataverse, etc.
This paper has a major main contribution in the literature by presenting clearly and gradually the way in which the determinations and interpretations of the results were performed.
Author Response
Reviewer 3 has no specific questions we need to address.
