This study compares the difference between in situ and remote sensing observations for air pollutants in from different perspectives over Canadian Oil Sands. The manuscript is pretty informative. However, the key contribution and findings are not clear, the large number of acronyms are difficult to follow, and the text is really long and it is suggested to keep it succinct. Detailed comments are given below:

Abstract

Line starting with ‘Compared to an in situ instrument that provides…’, that applies to nadir sensors, limb and occultation sensors provide vertical profiles.

Line starting with ‘Elevated SO2 VCDs are clearly observed…’, are observed or were observed?

Do not mix-use British or American English, like analyzed and modelled, keep consistency

Line starting with ‘In addition to measured wind…’ Maybe not all readers across the world know what ERA-5 reanalysis is, it is a good practice to give its full form at the first appearance.

Line starting with ‘The results show that…’ The findings are not significantly strong or exciting to intrigue the readers.

Introduction

Maybe not ‘even’ in polluted urban areas, my guess is relatively high correlation is expected in un- or less polluted areas for NO2, SO2, except for O3.

Authors may want to use acronyms less to help readers follow the storyline clearly instead of wondering the meaning of individual acronyms.

Ln 15, we compare or compared?

Ln 20, the cause of what?

Ln 20 again, what is the major difference of definitions on ground-level and in situ observations?

Ln 25, this bit ‘integration period differences’ comes out of sudden, readers may want to know why do we care about the integration period.

Section 2

It would be lovely to have a map of the study area that makes the paper more illustrative.

Ln 5 What would the inspiration of this study be as the Fort McKay is a very small town? How would people be informed and apply the findings here to other polluted regions, as most heavy pollution that threatens people’s life occur at densely populated urban areas.

Ln 5 I do suggest the authors use acronyms less to make the life of readers easier.

Section 2.1

Just curious, would it be considered as a ‘recently developed’ instrument as it has at least ten years of history?

Ln 30 What is U340 bandpass filter? What is ECCC? What is PGN?

Ln 5 no. 104, does this serial number really matter?

Ln 10 ‘…is given by (Herman et al., 2009)’ is not a good format for reference.

Ln 10 How does this Pratmo box model work and why it can remove NO2 in the stratosphere? Sometimes it’s not the case the more information the merrier.

Ln 15 What does the retrieved SO2 refer to? Is it from OMI? If it’s from a project, we need a reference to it.

Section 2.4

What is Q-switch Nd:YAG?

Section 3

What are coincident observations? Do the authors mean overlapped observations?

P9 Ln 5 What are selected wind directions? How did the authors do the selection, do you mean upwind or prevalent direction?

Conclusion

It would be better to have a concise conclusion