It's known that humans breathe mostly through one nostril at a time. How can we then perceive the direction the smell is coming from? Some articles claim similarity between olfactory and auditory directional perception:
The direction of a sound source can be determined binaurally by using the time difference and the loudness difference of the sound waves arriving at the two ears. Similarly, the direction of an olfactory source can be determined by using the time difference and the difference in sensation magnitude of the olfactory stimuli between the two nostrils as the air surrounding the odorous object is inhaled. Time differences of the order of 0.1 msec can be recognized—a value similar to that found in hearing.
However, that explanation runs afoul of breathing mostly through only one nostril at a time because at least the
difference in sensation magnitude of the olfactory stimuli should depend heavily on which nostril is 85% shut and which one is wide open.