Air contains about 300 ppm of CO2 and the effect of CO2 in air on the pH of distilled water can be readily calculated (might be able to look it up in published literature). As a first pass, the presence of NaCl (salt of a strong acid and strong base) would level the pH effect somewhat. Thus we would have placed some boundaries on the effect. Next, I would use a process simulator that has an ionic solution option (and enable the pH calculation switch) to see if some additional guidance can be had.

John Corn