1. Walnuts and motorbike brake pads.
2. A pile of wet clothes after a day in the snow.
3. Welding fumes.
The best description I can come up with is metallic; a rather pleasant sweet metallic sensation. It reminded me of my college summers where I labored for many hours with an arc welding torch repairing heavy equipment for a small logging outfit. It reminded me of pleasant sweet smelling welding fumes.
Astronomers announced in 2009 that a dust cloud at the centre of our galaxy contains ethyl formate. Ethyl formate is the chemical that gives raspberries their distinct flavour, but actually smells of rum.
All I can say is that everyone's instant impression of the smell was that of spent gunpowder, not that it was 'metallic' or 'acrid'. Spent gunpowder smell probably was much more implanted in our memories than other comparable odors.
6. Burnt charcoal.
It was like burnt charcoal, or similar to the ashes that are in a fireplace, especially if you sprinkle a little water on them.
When you repressurize the airlock and get out of your suit, there is a distinct odor of ozone, a faint acrid smell.
8. Burnt almond cookies.
They said it is a very unique smell. As they pulled the hatch open on the Soyuz side, I smelled "SPACE." It was strange… kind of like burned almond cookie.
9. Seared steak and hot metal.
When astronauts come in from a spacewalk and remove their helmets, they've reported smells of "seared steak," "hot metal" and "arc welding on their motorbike."These are all consistent descriptions, not flukes. That led us to conclude that the sensation is caused by some high-energy vibrations in particles brought back inside which mix with the air.