Laundry that’s dried in the open air always smells so good, now science has identified the sources for that fresh scent. Ozone and sunlight reach with materials in a wet garment, creating aldehydes and ketones, according to a study at the University of Copenhagen. For instance, line-dried towels emitted pentanal, a fruity-smelling compound found in cardamom; octanal, creating citrusy aromas; and nonanal with a rose-like odor. Sun-dried towels are loaded with fragrances catalyzed by the sun that smell good.