I think you may want to have a look at ASME PTC 10.
My basic understanding is that if you want to compress a differing gas to the design MW then the performance will change not just because of density but also because of the aerodynamic speed change. The aerodynamic speed is mechanical speed...
Aqueous Ammonia storage usually has a very small scrubber attached, made from a 300 mm NB pipe with about 2 m of 15 mm Pall Rings. The scrubbing solution is then a very small, say 1 m^3/h trickle of water. This scrubber only takes care of general tank breathing due to diurnal temperature swings...