Please see the attached supplement for my review comments.

## General comments

The manuscript introduces a method to assess the spatial scales of local aerosol production in boreal forest and agricultural ecosystem. Following the footprint estimation via Lagrangian dispersion modelling to assess flux footprints they develop a source contribution function for aerosol particles in the size range of 2-2.3 nm which can be related to the local sources of needed precursor gases and the favorite atmosperic conditions.

The manuscript has some aspects that may need a bit deeper explanations. As example, the prerequisite of a neutral stratification and the limit to this conditions is mentioned but it remains unclear why that limitation was chosen.

## Specific comments

page 1, line 5: "to produce small particles predominantly from own emissions." It is not immediatly clear what these "own emissions" are. You speak about "an ecosystem" therefore I assume the "own" relates to this ecosystem, in that case I would at least write "its own emissions".

page 1, line 10: What do you mean with "below-canopy forest"? Is that the understory layer? Is it a supressed canopy layer?

page 1, line 11: "For the distribution close to measurements, the contribution of the nearby 100-500 m is approximately 30% in agricultural fields." What distribution do you refer to? It leaves me thinking what if that distribution is not near to measurements? Why the 100-500 m, that are a feature of the forest (in the sentence before), are now some fraction of the agricultural field?

page 6, line 178ff: You emphasize that the footprint function is itself not time depended? Where do you get this statement from? I ask because later in the manuscript (page 8, line 240) you tell that your Lagrangian dispersion model calculates according the travel time of air parcels. Furthermore you tell in Appendix B that the model used Gaussian distributions of velocity fluctuations. Velocities usually have a unit of m/s, so an explicit relation to time.

page 6, line 184ff: The two subsequent sentences "Our concept of the source contribution function of local aerosol production is related to the concentration footprint for non-inert trace gases as we consider also the time scales of aerosol dynamics.Our concept of the source contribution function of local aerosol production is related to the concentration footprint for organic vapours (inert scalar) but considers also the time scales of aerosol dynamics." seem to tell the same thing. Maybe that remained accidentially while revising or, as AI helpers become more popular, these tend to repeat text with slightly different wording over and over. Maybe decide which version to retain.

page 10, line 310 and page 11, line 327: Figure number reference not resolved in the text.

page 11, line 349: "the concept of the footprint of the turbulent transport," I am not sure if I understand that statement. Turbulent transport "determines" the footprint (the field of view of the sensor). Why the "concept"?

page 12, line 358: "Above the canopy, the behaviour seems..." I would add like so " Above the canopy, the behaviour of forests seems..."

page 14, line 438: You tell that you are using the forward trajectory method. Can you explain why that choice was taken? Backward method is reported (e.g., Vesala 2008) to allow efficient application in case of inhomogenous terrain which is more apparent than homogenous terrain.