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Physicist struggling to figure out how to calculate the concentration of gas above aqueous ammonia

I am a physicist who has run into some chemistry in the lab (and unfortunately, I’ve completely evaded any formal training in chemistry). I have exposed some samples (I think details of the sample are not important here, but would be happy to provide further information if necessary) to a solution of 30% ammonia and 70% water, and am trying to calculate approximately how much ammonia (in ppm, for example) reached my sample. My samples are placed in an 3(L)x3(W)x1(H) (inches) container with the top exposed to the air. Until now, I’ve just been marking down the volume of the solution that I’ve placed (about 15 mm) directly below my samples in the container (e.g., 5uL, 10uL, …, up 200uL). I think it’s good enough to assume room temperature and standard atmospheric pressure for my labs. I’ve looked into Henry’s law and related relationships, but am not sure that these are the appropriate tools. I would greatly appreciate any help or guidance!

Maybe these tables will help (I’ve stumbled upon them trying to figure this out in the context of Henry’s law):


If a closed container is a more tractable problem, I also collected some data with a closed container (same dimensions), and would very much appreciate insight into that problem too (if it is very different, or the only solvable problem). I should also mention that the solution was removed from the container in about 10 seconds in all cases (if that makes a difference). Thanks again!

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