Clothes dried outside smell better because of a process called photolysis (sunlight breaks down compounds that cause odor).
Floral, fruity, citrusy — clothes just smell better when they are dried in the sun rather than in a drier or hung indoors. But what gives them their extra fresh scent?
A group of researchers at the University of Copenhagen’s Department of Chemistry looked into this question, releasing their findings in an article published earlier this year. The researchers found a dark empty office in the chemistry building and a sunny balcony where they hung uncolored cotton towels up to dry.
The towels had been washed three times by hand, in ultra-clean water in which there were no particles, microorganisms, or salts. By comparing the differently dried towels, the researchers discovered that those that had been sun-dried produced a range of aldehydes and ketones: organic compounds that our noses associate with the scent of plants or perfume.
"The sun-dried towels clearly had the highest concentrations of oxidized compounds (fragrances). In other words, the sun catalyzed photochemical processes that created the fragrances that we found," explains Ph.D. Malte Frydenlund, one of the UCPH researchers behind the study. For example, line-dried towels emitted pentanal, a compound found in cardamom, octanal, which emits citrus-like aromas, and nonanal, which has a rose-like odor.