Here are ways to freshen it up.
Once a month to keep your garbage disposal and fresh smelling: Grind about a dozen ice cubes made with white vinegar. The ice sharpens the blades while the vinegar deodorizes the drain.
Salt will clear out the gunk that collects in the garbage disposal and the smell that goes along with it. Pour a few spoonfuls in and flush with cold water, them run the disposal.
Stinky odors coming from the microwave? Just cut a lemon in quarters and put it in a bowl of water, then put in microwave on high for two minutes.
Popcorn made in the microwave can leave lingering odors, especially if it burned. Just take a tea bag (even a used one) placed in the microwave for a minute is all you need to eliminate that stale smell.
Self-cleaning ovens are great but can leave an odor after it's done. Eliminate the smell by turning down the oven to 350°F when finished, then put orange peels on a baking sheet inside. Cook the peels for a half an hour. Not only will the oven smell fresh, but your kitchen will too.
If you are a tea drinker and hate to throw anything away, place them in a bowl and put them at the back your refrigerator. They'll remove odors just as well as baking soda!