I’m still missing something here. For it to be useful, I’d imagine that it would need to inform decisions, and do so where existing senses would fail.

At least in my environment, if I can smell rain, I could also just as easily use my eyes to see the cumulonimbus clouds and say “rain, due east”.

In the savanna are there scenarios where the only awareness of rain would be smelling it? Can you derive directionality at 5 parts per trillion? Does it matter?