I think the following two referees’ comments are not adequately addressed. The manuscript should be publishable after you properly address these in the revised manuscript.

(1) Estimation of ionization production. You acknowledged that “Q was probably much higher than suggested by the NAIS measurements.” How higher is “much higher”? Could you provide a quantitative best estimation? In the abstract you mentioned that “The “Waldstein” research site is located in a spruce forest in NE Bavaria, Southern Germany, known for enhanced radon concentrations, presumably leading to elevated ionization rates.” Does this imply the ionization rate at this site higher than that in Hyytiala?

(2) Uncertainties of NAIS.
You cited several previous publications about the uncertainties. Please summarize the major uncertainties in your manuscript.

In page 13, you pointed out that “it generally underestimates the ion concentrations and overestimates the total particle concentrations.” Please provide more details (reasons behind these and magnitudes) and references.