Chemical analysis and origin of the smell of line-dried laundry

Environmental context The fresh pleasant smell of laundry dried outside in sunlight is recognised by most people, but despite decades of speculation the origin of the smell has not been demonstrated. We show that the smell of line-dried laundry is due to the unique combination of traces of atmospheric hydrocarbons, sunlight and a wet fabric surface. This surface photochemistry is likely to be widespread in the environment on surfaces of natural materials. Abstract In this study, we find that the drying method is the key element in generating the well-known fresh scent of line-dried laundry, which we argue demonstrates that it is the result of physical and chemical processes occurring on the surface of the fabric. Cotton towels were rinsed with Milli-Q water and dried outdoors, indoors, and outdoors but not exposed to sunlight. The dried towels were placed in sealed Tedlar bags, and the emitted compounds were analysed by using thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) to yield qualitative gas chromatograms and mass spectra. We observed a variety of C5 to C9 oxidised carbon compounds (e.g. aldehydes such as pentanal, hexanal, heptanal, octanal, and nonanal) when the towels were dried outside. These compounds are not observed in the other conditions. Many of these compounds have smells that are subjectively found to be pleasant. The experiments indicate that both UV light and the presence of liquid water are necessary to generate the products. The polar nature of the oxidised compounds may explain why the smell of fresh laundry is relatively long-lasting because hydrogen bonds can form between these compounds and cotton fibres. We therefore propose that oxidative photochemistry on the surface of the drying laundry is responsible for the production of the fresh smell.