Dryers might be quick and convenient, but there’s nothing like the smell of laundry left to dry outside in the sun. It got some chemists wondering—what is that smell, exactly?
To find out, they gathered up cotton towels and washed them several times in extremely clean water. Then they hung them up in three places: some in an empty office in the chemistry building, some on a shaded balcony, and some on a sunny balcony. After the towels had dried, they were sealed in plastic bags for 15 hours so the chemical compounds on the towels could be released from the material and trapped in the bags. Scientists then sucked the air out and analyzed it.
Unlike the towels dried inside or in the shade, the towels dried on the sunny balcony were saturated with organic compounds called aldehydes and ketones that our noses associate with the smells of plants and perfumes. These compounds included pentanal, which is found in cardamom; octanal, which smells like citrus; and nonanal, which smells like roses. Other compounds were ones we associate with scents like chocolate, herbs, fruit, wine, almonds, and leaves.
How did these compounds get there? Scientists think two ingredients were crucial: sunlight and the presence of liquid water. Ozone in the air might be reacting with molecules in the wet towel to produce the aldehydes and ketones. The UV light from the sun might also be prompting their creation. It’s likely that the same reaction is happening on a lot of surfaces in nature.