When you store a variety of foods in one place, they all start to spread their smells around. Onion, fish, and other potent flavors can seep into your food. It can be rather obvious which foods have affected as they don’t taste as fresh. The general smell of the fridge can also be rather abhorrent if you left food in there for too long.
If you want your fridge to smell as it should (like nothing), then you might want a Kuro Cube. This block of compressed white charcoal will suck up any unsavory gasses, which will help to extend the lifespan of your food in addition to making your fridge a little more tolerable to open. This little air purifier can be used elsewhere too, and will remain active for five years so long as you put it in the sun to dry out every now and again. This is a $25 purchase that will only take less than three cubic inches of space in your fridge.