Review of the article “Towards near-real time air pollutant and greenhouse gas emissions: lessons learned from multiple estimates during the COVID-19 Pandemic” by M. Guevara et al.

This is an interesting piece of work comparing European emission inventories for the year 2020 and how they reflect the impact of the emission reductions caused by lockdown measures taken to prevent the spread of the COVID-19 virus. The idea behind the analysis is that lessons can be learned about the construction of near-real-time emission inventories that will be able to reflect large unexpected short term changes in emissions. This is a very valuable exercise and the conclusions that the authors draw are worth to be published and brought to a wider audience.

I recommend publication of this work after few smaller modifications.

Detailed comments:

Line 32: between -29.3 and -5.6 %

Line 73: give examples which countries reported quarterly and monthly emission estimates.

Line 151 -154: reformulate this sentence. It can be read as if you use shipping mobility statistics for aviation emission. It remains also unclear what exactly shipping mobility statistics is and where the data can be found.

Table 2: For Forster et al the emission changes in aviation and shipping are given to be based on a previous publication by Le Quéré et al. Could you say how they derived their adjustment factors for these sectors?

Line 189 – 191: It would be nice if you could say more about the differences for the shipping sector. If some authors report only global changes, this means that they apply the same reductions in Europe and you should be able to compare those to the factors calculated with the STEAM model.

Figure 1: Would be good to include GNFR sector names in addition to the letters, similar to Tables 3 and 4.

Line 262: omit one “slightly”

Line 373 – 385, section 3.1.6 Road transport: CO₂ from road transport is shown in Figure 5d, however, this sub-figure is never mentioned in the text, and its contents is only touched upon. You might write a bit more about Figure 5d and also make clearer when you talk about NO_x and when about CO₂.

Line 415: Figure 3a and 3b don’t fit together into one. They show very different things and are mentioned at very different places in the text.

Line 589/590: how difficult it is

References:

give last access date for Kinsey (2020)

The paper "Towards near-real time air pollutant and greenhouse gas emissions: lessons learned from multiple estimates during the COVID-19 Pandemic" by Guevara et al. provides a very useful comparison of several "real time" estimates and official inventory data.

The paper is well written and provides a very useful and informative analysis. I have only two comments.

One minor point that should be added is that the official inventory estimates for 2020 are also approximations of actual emissions. There are two components of this. Of course all inventories may contain errors. However, more relevant for this comparison, is that inventory estimates for the last year published often change in subsequent revisions as underlying data (such as energy statistics) and other information is updated or revised. I suspect this won't impact the comparisons for the most part, but occasionally (for some country/sector combinations) this might have a signifiant impact.

The collection of these various inventory data took some signifiant work and, while all the data are publicly available, it would be laborious for someone to replicate the work done by the authors. The authors should, as a supplmental data file, supply the following information: annual emissions and/or adjustment factors (as appropriate) by country/sector/year, and the same data by month (where available). This would make the analysis in this paper more readily useful to the community since the comparisons could then easily be extract for any country/sector of interest for use in subsequent analysis.