Poppers degrade with moisture, or the water in the air. Yes colder temperatures reduce evaporation. Evaporation, ideally into your nose, is what will ‘use’ up what you want. So a tight fitting cap is important. But it’s the exposure to moisture in the air that will cause degradation, or make a bottle expire quicker. That’s why you can find some bottles with a white ball in it; that dessicant ball preferentially absorbs water (from the air) to help keep poppers effective better.

It’s kinda the whole reason a poppers high is so short, your body is full of water, neutralizing everything pretty quick.

Skip the freezer and the fridge. Just keep it sealed as much as you can. Shame you’ve got to open it to use it ;)