Grimy windows could be harbouring toxic pollutants
16 Sep 2022
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Dirty windows can harbour potentially harmful pollutants under protective films of fatty acids from cooking emissions – and these can hang around for long periods of time.

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According to a new study, the fatty acids emitted during cooking are highly stable and not easily broken down in the atmosphere. That means that, when they hit a solid surface such as a window, they form a self-organised thin film that builds up over time and will only be very slowly broken down by other chemicals in the atmosphere. 

During this process, the film will become rougher and attract more water from the humidity in the air. In addition, toxic pollutants can become trapped underneath this persistent crust and are then protected from breakdown in the atmosphere. Dr Christian Pfrang from the University of Birmingham said: “The fatty acids in these films are not, by themselves, particularly harmful – but because they are not being broken down, they are effectively protecting any other pollutants that might be trapped underneath." 

In the study, which features on the inside front cover of Environmental Science: Atmospheres, the team studied laboratory 'proxies', engineered in the lab to act as a model of 'real world' samples. These were spun into super-thin films of pollution, just a few tens of nanometres in thickness. 

The researchers used the INTER beamline at ISIS, as well as experiments at Diamond Light Source and the ILL to study the nano-scale composition of the films and the changes in their surface structures. By changing the humidity and amount of ozone, which is a key pollutant indoors and outdoors, the researchers were also able to mimic the behaviour of the films over time. 

They found that the self-organised arrangement within the films in repeating molecular sheets, known as a lamellar phase, made it difficult for smaller molecules such as ozone to access the reactive parts of the fatty acids within these structures. Once deposited and exposed to ozone, the surfaces of the films became less smooth and increasingly likely to take up water, an effect which also has implications for the formation and lifetime of aerosols in the atmosphere. 

The full paper can be found at: The evolution of surface struct​ure during simulated atmospheric ageing of nano-scale coatings of an organic surfactant aerosol proxy.

Contact: de Laune, Rosie (STFC,RAL,ISIS)