Response to the commentary by Pisoni E. and Van Dingenen R. on ‘Assessing nitrogen dioxide (NO₂) levels as a contributing factor to coronavirus (COVID-19) fatality’

Dear Editor

I wish to thank Dr. Enrico Pisoni and Dr. Rita Van Dingenen for their effort to write comments on my recent paper “Assessing nitrogen dioxide (NO ₂) levels as a contributing factor to coronavirus (COVID-19) fatality” (Ogen, 2020a). I will answer all their comments as they appear in the letter to the editor.

Answer to comment 1:

I agree with the comment about the limitation of satellite data. This data provides a spatial assessment of the NO₂ concentration of a large area. However, even the ground-level NO₂ measurement has limitation because it is valid only to the place of measurement and it is not possible to conclude about a certain area using this data. Therefore, the satellite, although it has its own limitations, provides continuous spatial NO₂ data even in remote regions where no in-situ device is found. I should add that the absolute value itself is not important for the frame of my article but the relative value. The main conclusion of my research was that the high fatalities due to COVID-19 were observed in regions with high NO2 concentrations provided by the Sentinel 5.

The figures provided by the authors (Figs. 1, 2) show the annual mean NO₂ concentrations observed at traffic stations in 2017, while the satellite image shows not only different periods (the two winter months January–February) but also different years (2020). Even if we assume that we can compare the two figures, the points in Fig. 2 are traffic stations which are located close to the emission sources (near roads, highways etc.) and therefore provide high NO₂ values. These stations are not equally distributed, and their locations were chosen carefully. Therefore, the question is whether we can trust also the in-situ data for assessing the impact of air pollution on COVID-19? From my point of view, we cannot.

The boxplots shown in Fig. 3 are also not comparable. The data used in my article covers 66 regions in four different countries while the boxplots show a summary on the country level and the data is not equally distributed in space.

Answer to comment 2:

The onset is different for each country. But it is also different for each region and each city. We can always go more into higher and higher resolutions and that would cause the data to be meaningless when the purpose is to publish preliminary results in a short communication manuscript.

Answer to comment 3:

I do agree. Different countries reported it differently. If so, no research can or should be conducted using this dataset. Regarding to this remark, should the research stop? The data was provided from reliable sources and while conducting the research it also seems trustworthy.

Answer to comment 4:

I agree that correlation is not causality. See my comments on that in Ogen (2020b) for more details.

Answer to comment 5:

The number of deaths is related also to the number of people living in the region and to the number of people that were exposed to the virus. In the UK there are 66.6 million people and in Italy 60.4 million people. Additionally, the lockdown in the UK started several weeks after Italy.

Concluding remark:

To summarize, my study ‘Assessing nitrogen dioxide (NO ₂) levels as a contributing factor to coronavirus (COVID-19) fatality’ was one of the first to shift the focus from the pre-existing diseases to the pre-existing environmental condition. During that time, the global community was thirsty for innovative ideas to tackle the global crisis and as a researcher, it was my great privilege to serve that purpose.

Declaration of competing interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.