Dirty windows can harbour potentially harmful pollutants under protective films of fatty acids from cooking emissions, which can linger for a long time.
According to a new study led by University of Birmingham researchers, the fatty acids found in cooking emissions are highly stable and difficult to break down in the atmosphere.
That is, when they collide with a solid surface, such as a window, they form a self-organized thin film that accumulates over time and is only slowly broken down by other chemicals in the atmosphere. During this process, the film becomes rougher and attracts more water from the air’s humidity. Furthermore, toxic pollutants can become trapped beneath this persistent crust and thus protected from degradation in the atmosphere.
According to senior author Dr. Christian Pfrang, “the fatty acids in these films are not particularly harmful in and of themselves—but because they are not broken down, they effectively protect any other pollutants that may be trapped beneath.”
The research, which appears on the front cover of Environmental Science: Atmospheres, was conducted in collaboration with experts from the University of Bath, Diamond Light Source, ISIS Neutron and Muon Source, and the Institut Laue-Langevin in France.
The team worked on laboratory proxies, which are material samples engineered in the lab to resemble’real world’ samples. These were spun into super-thin pollution films a few tens of nanometers thick.
The researchers studied the nano-scale composition of the films as well as changes in their surface structures using neutrons and X-rays. The researchers were also able to mimic the behaviour of the films over time by changing the humidity and amount of ozone—a key pollutant both indoors and outdoors.
They discovered that the self-organized arrangement of the films in repeating molecular sheets, known as the lamellar phase, made it difficult for smaller molecules, such as ozone, to access the reactive parts of the fatty acids within these structures. When the films were deposited and exposed to ozone, their surfaces became less smooth and more likely to absorb water, an effect that has implications for the formation and lifetime of aerosols in the atmosphere.
