I am happy to accept your paper for final publication as a Letter in ACP subject to some relatively minor further changes:

1) Please consider the location and naming of Table 1/S1 and whether (as requested by the reviewer) it is possible to add some observational data. If you intend it to be in the appendix then please name it Table A1.

2) You are not consistent in your use of the words aerosol, aerosols and particles. In most cases the word particle would be most appropriate (particles have acidity, not the aerosol). When referring to aerosol in multiple locations then the plural is acceptable, otherwise the word aerosols is not a synonym of particles. You also use the word particulate as an adjective in the abstract where it should be a noun (particle mass).

3) The final sentence of the abstract is somewhat vague. What control strategies are you referring to in the context of climate change? The abstract up to this point has been only about pH, so it is a large leap for readers to understand the link between pH and climate, which is presumably though particle hygroscopicity and size. Rather than being a speculative statement, please try to link this sentence more to the findings described in your paper. The conclusions could also explain this link in a bit more detail so that this sentence is linked to a longer description in the paper.

Before final acceptance I would like to make some additional recommendations based on the modifications you made in response to my comments.

1) Please correct the error "decreased" on line 181. You may want to double check that throughout the paper you do not have the same mistake in terms of increased acidity/decreased pH. It's easily done.

2) I think your abstract could summarise better the key result. I suggest to start a new sentence at "and uncovered remarkable variability..." and add something about the increases and decreases over Europe, N America and Asia. E.g., "The simulations uncover..." You may slightly exceed the 200 word limit, but please try to reduce back if feasible.

3) Regarding "aerosol particle". You are mostly consistent now, but there are a few places where you talk about aerosol acidity (in the abstract) or aerosol in place of particle. I don't think it is necessary to say aerosol particle every time. Once you have introduced in the abstract/intro that you are discussing aerosol particles (rather than cloud particles) then it is sufficient to just refer to particle pH, particle acidity, etc. Sorry if my previous comment was not clear.

Thank you for choosing ACP Letters for this excellent paper that provides the state of art of knowledge on pH changes over the past 50 years with findings that have implications for climate, biogeochemical cycles and air pollution/health. I fully agree with the handling editor assessment to publish the manuscript as an ACP Letter.