The manuscript has certainly a scientific interest in horizontal lidar signals processing, introducing a novel method for reference values retrieval. The presentation is clear and it is in the scope of ATM. 

There are other methods to retrieve the horizontal PM concentrations based on lidar and synergies with PM measurements. All of them were correctly referenced (ie: Ma et al., 2019), and the differences between them were correctly mentioned, producing this novel method with more stable results under inhomogeneous aerosol conditions.

The manuscript provides a method to retrieve concentration maps by combining lidar and in-situ PM concentration measurements. It remarks on the limitation of this measurement to in-situ measurements and highlights the importance of remote PM measurements.

The conclusions are correctly reached, supported by figures where the stability of the results using the new algorithm is conclusive. 

Specific comments:

I have minor concerns which I pointed out in the attached supplement. Please, read the annotations I made in the highlighted text inside the file egusphere-2023-2138-manuscript-RC_1.pdf. 

My main concern about the manuscript is the clarity of some procedures, being hard to be able to reproduce them.

The description of the method to obtain alpha_ref is not totally clear to me. Lines 119-131 mention the identification of the reference distance (r_ref) but end using 5 km for a reason that I don't understand. 

In my opinion, the descriptions should be expanded to increase clarification in order to be reproduced by the community. 

I would like to read more information about the implementation of the Angstrom exponent and the discrimination of the aerosol alpha profile in fine and coarse particles.

General comments:

The manuscript is well written and documented with a sufficient number of relevant references. Minor changes are required to be fuller and more comprehensible.

Retrieving aerosol properties in horizontal plane is an open issue and here a new scientific approach is suggested.  However, a more detailed analysis should be presented, revealing all steps and constants/assumptions used here.

Specific comments:

Plots:  A grid like the one applied in Figure 2a would be helpful to be applied in all relevant plots also. Wavelength (532 & 1064 nm) should be presented in a clearer way in all sub-figures. E.g., include it as a title or legend.

Ln 34-36: Please correct near-zenith measurement, means pointing almost vertically in the atmosphere, therefore, “in measurements with higher elevation angles” should be changed to “in measurements with low elevation angles.”

Ln56-57: you mention that “Backscattering at 532 nm is split into a parallel and a perpendicular signal with respect to the linearly polarised emitted laser light”. However, it is not clear to me if the parallel, cross or the combination of both components are used for the analysis of retrieving the PM concentrations.  Is the depolarization channel useful somehow in your method or is it just an additional feature of the lidar?

Ln 66-70: Please provide more details about retrieving PM concentrations. How was the separation of fine and coarse particles performed? What assumptions/constants were considered?

Ln 86: Please make clear what the special resolution of the lidar is.

Ln 87: What technique/equation was applied to calculate the signal-to-noise ratio (SNR) ? Please mention.

Ln97-98: “Second, as any point in the scanned area could be an emission source, it is more likely that the reference distance for the Fernald-Klett inversion is a function of scan angles.” This sentence is a bit confusing to me. Is this indeed your second assumption of your method? Your method works only for multi-scanning measurements? What about horizontal measurements fixed in a specific direction?

Ln105: “…where we would expect to see background values” background values usually refer to atmospheric background and therefore molecular atmosphere which is not the case for horizontal measurements. Please rephrase.

Ln179: “… by users without lidar expertise”. Please remove. This does not offer something to the discussion and is not derived as a conclusion from the above.