How would atmosphere density affect smell?

Question

So I have this idea for a creature that has a loop arch on its face. My only explanation for why is because it needs extra surface area for its sense of smell. But then I wondered what would warrant the need for so much surface area just to smell? Would dense air require it because there's more air to sort through, or thin air since they need a bigger sample size?

Answer 1

What makes a smell stronger or weaker has as much to do to do with the receptors we have as with the concentration of substances or air pressure. According to the Wikipedia article on farts:

Over 99% of the volume of flatus is composed of non-smelly gases.

By the way, there is real sciencing going on here:

The remaining trace (<1% volume) compounds give flatus its smell. Historically, compounds such as indole, skatole, ammonia and short chain fatty acids were thought to cause the smell of flatus. More recent evidence proves that the major contribution to the smell of flatus comes from a combination of volatile sulfur compounds (...) These results were generated from subjects who were eating a diet high in pinto beans to stimulate flatus production

And also:

Normal flatus volume is 476 to 1491 mL per 24 hours. This variability between individuals is greatly dependent upon diet. Similarly, the number of flatus episodes per day is variable; the normal range is given as 8–20 per day. The volume of flatus associated with each flatulence event again varies (5–375 mL).

An average fart of 100 mL (implying about 1 mL of smelly gases) may be easily perceived across a 360 m³ classroom. The concentration of active fart smelly gases by volume in this example is 0.00000000027%. Doubling or halving the atmospheric pressure would be equivalent to doubling or halving the area of the room, which would affect that concentration very slightly. Changing the atmospheric pressure to further extremes may not do for prolonged human life, in case you wish your creatures to live in the same world as humans.

The need to perceive smells at low concentrations will push towards more olfactory tissue area regardless of atmosphere. More olfactory tissue also allows for more varied receptors, which is why dogs are so good at identifying stuff, other dogs and people by smell. That's what you should keep in mind.