The pH is less than 5.6 for "the non-polluted site" because of the presence of natural souces of sulfur and nitrogen in the atmosphere. Much work was done in the 1980's-1990's on identfying a non-anthropogenic influenced pH of rain and cloud water. We report on this and other work we did with clouds in a manuscript from a few years ago. See: Atmospheric Environment 45 (2011) 6669-6673