In an exemplary implementation, a semiconductor device includes a III-nitride heterojunction including a III-nitride barrier layer situated over a III-nitride channel layer to form a conduction channel including a two-dimensional electron gas. For each partition, a relevance of each event in a collection of events that occur at a time in the partition is determined based on the query. A transmission rate associated with the gas X is then computed from the relationship between the measurement results, the mass of the test film bag alone, and the surface area by a computer.