Mmm...I Smell Soup

When making chicken soup in the simplest way, I put the chicken in the pan, then water, after it starts to boil I remove the scum, then add onions, salt and pepper, and leave it to simmer for 35 minutes. When I use shredded onions, the smell of the soup smells yummy, as if your grandma just made soup. But when I just cut an onion into 4, the smell around the house is weaker. i.e. Use shredded onions in the soup better than just cut onions.