Dogs noses are incredibly powerful (up to 100,000 times more than human noses depending on breed). They have two functions: to breath and to smell. Unlike humans, dogs have two separate channels for the intake of breath; the olfactory region which takes in smells and the respiratory region which leads to the lungs.
When they breath in, the nose is able to separate the air from the scent through these two separate channels.
How does it work
The olfactory region of the nose contains up to 300 million scent receptor cells (humans have around 5 million) in a maze of tiny coated bones called turbinates. The smells are contained in this area, analysed and remembered by the brain, even when the dog breaths out. This is due to the fact that dogs can breathe in through the olfactory channel, at the same time as breathing out through the respiratory channel. This way the air is pushed out through the slits in the side of the dog’s nostril without having to breath out the smell.
The dog’s brain also includes a much larger olfactory cortex (or bulb) than human's, around 40 times larger, which accounts for around 1/8 of the dog’s brain. This bulb is responsible for processing scents and information and storing scent information and scent memory.
Dogs also have an additional organ as part of the olfactory system, which is not functional in humans, called the vomeronasal organ. This organ is responsible for detecting pheromones, human emotions, the intentions of other dogs etc.
Amazingly, dogs can also smell separately with each nostril giving them the ability to smell in 3-D. This allows them to pinpoint exactly where the smell is coming from and find food (amongst other things).