Please see attached file for comments and feedback. 

General comments:

In this manuscript, the time series of vehicular emissions of NO_x and EC before and during the 2020 lockdown as well as the averaged time series of NO_x over the same period for the previous four years (i.e., the mean of 2016-2019) were compared and used to train the machine learning model, rebuilding the NO_x and EC in a business-as-usual scenario in 2020. This study improves the understanding of the trend in vehicular emissions and, in particular, in response to the strict Covid-19 lockdown based on the long-term observation dataset and application of advanced mathematical models.

My specific remarks are given below, after a minor revision the manuscript can be accepted.

Specific remarks:

- 1. Line 45: "NO₂ concentrations are" --> "NO₂ concentration is"

- 2. Line 46: "NO_x (NO+NO₂) emissions" --> "NO_x (NO+NO₂) emission"

- 3. Lines 50-51: "elemental carbon (EC) or black carbon is emitted a result of incomplete combustion of fossil fuel (gasoline and diesel) in the internal combustion engine", this description is not sufficiently rigorous. The incomplete combustion of biomass is also the one source of elemental carbon (EC) or black carbon. This description should be rewritten.

- 4. Lines 53-56: The duplicate content "with the recent implementation of high emission standards (e.g., China IV and V)" should be deleted to make sentence more concise.

- 5. Line 165: "measures (Grange et al., 2021)Specifically," --> "measures (Grange et al., 2021). Specifically,"

- 6. Line 202: "DOY" Please give the full name day of the year (DOY).