It helps to know what gas or gases. I am assuming this is natural gas, and not a gas mask. I do not know how to do the math or if it is possible to get from say the iodine test to porosity in say angstroms.
This might be closer to what you are looking for: https://sci-hub.se/https://doi.org/10.1016/0008-6223(95)00128-X
There might be something useful in this thread as well: