I'd say that in itself, dry NaCl aerosols (i.e. salt in christal form) do not carry any charge. That does not mean that these particles cannot be charged by a separate process.

 Individual aerosol particles are expected to be charged as the result of the formation process.  The expected net charge is zero. Some processes may result in a net positive or negative charge because the production of the particles results in stripping or adding electrons to the particle by the producing substrate.

Did the research paper describe the production mechanism? What was the environment of the aerosols? Note: The NaCl will dry the immediate environment and grow in size unless the environment is intentionally dried.

Personal experience with producing NaCl aerosols by evaporation, grinding, and solutions did not produce charging effects that adversely affected transport in a dry environment.

1st question for you

Which paper is your reference

then how are the particles produced

and a preliminary answer: when they are produced by nebulizing they do carry a small charge

The reference of the question could by this paper??

https://www.thesaltz.com/wp-content/uploads/Halotherapy.pdf

@ Ingo Ries

indeed I see the obscure parameter nK/m3

I have another ref

the mechanics of inhaled pharmaceutical aerosols

by Wayne, the new editor in chief of Aerosol Science and Technology; the leading American aerosol magazine in aerosol science

the part on charge on aerosol produced by nebulizing is for free in google.books

Are you the sales representative for the Russian halotherapy system?

I have comments about the reference

1. Dry aerosol will very rapidly take up water in the airways

2. The charge on the aerosol is still quite low and it will not very much influence the deposition. Only very small particles could deposit more effectively but there is very little mass in those small particles

I read your reference and then the brochure of the system mentioned there. It does not provide scientific information.

It seems that a dry generation is used and that the particles are sprayed with either negative ions. Rather small particles are generated which is not standard for a dry generation method.

In the Russian system negative is sprayed on the salt-particles. The particles are made in an apparatus

My question to you: how are the particles made in a cave? and how many

There is no ionic charger in a cave