It has been recognized for quite a while that the human nose is capable of recognizing over 1 trillion different odors. With the old favorites like cut grass, freshly baked bread, and the smell of new books all set to please those with a sense of smell, research has explained why laundry dried outside in the sun smells so much better than anything your tumble dryer could create.
Researchers from the University of Copenhagen published a paper back in 2020 all about the smells associated with washing dried by sunshine. They washed three towels by hand in water that was ultra-clean, meaning it contained no microorganisms or salts that could affect the smell of the towels.
For the drying process, the towels were then hung out to dry on three clotheslines in either a dark room, on a shaded balcony, or on a balcony exposed to sunlight. After the drying process, the towels were sealed in plastic bags for 15 hours, allowing the different chemicals to be released before the next test.
Air from each plastic bag was then analyzed via gas chromatography-mass spectrometry to identify the different chemical compounds present after each of the three drying scenarios. The team also took samples of the air from an empty bag and the air at each of the drying sites to compare with the dried towels.
The researchers found that towels dried on the sunny balcony had more chemicals such as aldehydes and ketones that are associated with perfume or the scent of plants. Both sets of towels dried outside also contained pentanal, which is found in cardamom; octanal, which is a citrus-like smell; and nonanal, which smells similar to the scent of rose flowers. The team has a working explanation as to why.
"When ozone in the air reacts with the materials in a wet towel, aldehydes and ketones are formed – which match the fragrances identified in the study. This could be part of the explanation. But we also think that there is something directly attributable to sunlight. For example, pigments or dyes in towels, found even when the towels are untreated, absorb sunlight and lead to chemical transformations,” said Malte Frydenlund of the University of Copenhagen, a coauthor of the study in a statement.
While the study might seem frivolous at first, the team suggest that research into the effect of sunlight on wet surfaces was lacking, and that studies like this can help give insights into how the degradation of different materials can occur.
"This mechanism can take place on nearly any exposed surface and is important for the degradation of substances in the environment. Therefore, it is incredibly important for us to gain insight into these processes. Hopefully, this study marks a step in that direction." concluded Frydenlund.