There is a part of our brain that stores emotional memories that is intricately linked with smell. As a result, if you ever noticed, there are some scents or aroma that reminds us of a past experiences and can flood us with the same long-ago feelings.
A lot of times, when I smell something familar, it instantly made me either happy or sad. Sometimes I can't remember right away the scent and how it relates to my past, but it is quite fun digging the story behind the scent.
Sure there are good smells and bad smells, but did you know that scents can also be happy or sad?