Why do some gasses have an odour while others are odourless?

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Why is it you can smell sulphur but you can’t smell nitrogen or oxygen?

And why does the air around some hot appliances have a distinctive odour. I can smell that my clothes iron is hot.

In: Chemistry

I believe it’s because some interact with chemical receptors in our noses while others don’t.

Nature has sculpted all living things through evolution for billions of years. Species tend to evolve ways to avoid deadly gasses. Sulfur for instance is highly toxic. We would want to be instinctually repulsed by that odor, otherwise our natural curiosity may end up killing us. I imagine the reason there are noxious gasses that are odorless is because they have become prevalent only in recent times. I’m pretty sure carbon monoxide isn’t a major threat in nature (if it is, maybe the native life would develop a method to detect it ). I would say it’s why lots of toxic foods and like, poop for example smells like, well, shit. When food rots, we are repulsed by it. Cats hate citrus and it happens to be toxic to them I believe.

Anyway I have no idea the bio-mechanism behind the actual detection of these molecules but I think we need specific receptors and also a brain designed to process the varying signals properly

Edit: typos

Around electronics or electrical applicanaces, you often smell ozone. Ozone is created when oxygen molecules in the presence of a lot of energy, fuse together to form a 3 atom molecule instead of a 2 atom molecule (the form oxygen takes naturally). We can’t smell oxygen, nitrogen, hydrogen, etc. normally because we literally are breathing that in all the time. Our bodies are good at ignoring something we smell all the time. You notice how if you are in the presence of a noxious odor, after a little while it doesn’t seem as bad? Our bodies ignore that signal after a while. So gasses we smell all the time we don’t even smell any more. I think evolutionarily speaking, this is good so we notice when the smell changes or we smell something different, such as hydrogen sulfide, sulfur, etc. that can be dangerous to us.

Odor is not a property of the gas.
Odor means that receptors in your nose interact with the gas, send electrical signals to your brain and the brain processes these signals to establish the sensation of ‘smell’.

Any sensation is an interaction between your sensors, your brain and the object that triggers your sensors.

You know that smell gas has? They put that in.
You see the gas is odorless but they add the smell so that you know when there’s a leak.

It would be more correct to say that some gases fall outside of the human ability to detect. I’ve read somewhere that dogs the ability of a dog to detect odors is anywhere between 10,000-100,000 times greater than ours.

It is wildly held that bears have the keenest sense of smell with polar bears reported can detect the scent of a seal through three feet of ice.

Hot appliances cause changes in their surrounding environment which can cause elements that have no detectable scent by humans at room temperature to become detectable at higher temperatures.

Think about a frozen pizza, at room temperature it does not smell strongly, but when heated in an oven, the scent is detectable throughout the house. Popcorn is also another good example.

Maybe we can smell oxygen but as it is all around us from birth we just dont notice?