pH in Wet Gas

If you are referring to a vapor as a wet gas, you can get, at least a general idea of the pH by wetting a piece of litmus paper with distilled water and putting the paper in the vapor.

H2S induced Cracking Damage Mechanisms.:_ One of the aspects considered API in the assessment of susceptibility to HIC and SOHIC is the pH and the amount of H2S in LIQUID phase. In a separator what is normally found is the H2S content is relatively low in the bottom of the tower (e.g. 20 ppmwt), whereas at the tower top the separated H2S gas is esentially still wet and having substantially higher H2S content (e.g. 2000 ppmwt). So how does one assess susceptibility to H2S induced HIC, SOHIC cracking damage mechanisms at the tower top / overhead lines, without the knowledge of pH in the WET Gas phase????? Hence the question on how pH can be measured in wet gas. ANY SUGGESTIONS?

Litmus paper will read the pH of a vapour as well as a liquid.

There's no need to wet it first afaik. Fumes, vapour pH will show.