Catalytic Poetry: ‘In Praise of Air

Air pollution is a growing problem and has a negative impact on our environment. Exposure to high levels of air pollution can cause skin irritation, and asthma attacks, it can also lead, in more extreme cases, to cardiovascular disease. As a result, cities are developing novel ways of tackling this problem head-on. One of these cities is Sheffield, whose air has been above the legal limit of nitrogen dioxide allowed since January 2010. Because of this, 500 deaths per year are associated with the air pollution in Sheffield. The council decided to team up with The University Of Sheffield in 2014 to help find a solution.

With the help of Prof. Tony Ryan from the Department of Chemistry, a 10 m by 20 m poster coated in photocatalytic nanoparticles of titanium dioxide was manufactured. This was displayed on the Alfred Denny building between 2014-2017 facing the concourse viaduct. Its surface incorporated a poem, In Praise Of Air written especially for the project by the, now, poet laureate, Prof. Simon Armitage from the School of English. Over the course of 4 years the poem removed over two tonnes of air pollution.

Titanium dioxide is a widely used photocatalyst due to its high photocatalytic activity, stability, low cost, non-corrosivity, non-toxicity, and high availability. It was used in this project to convert nitrous oxides, NOx, and volatile organic compounds, VOCs, from harmful air pollutants to harmless alternatives. When TiO2 particles are exposed to light of sufficient energy, a valence electron is promoted to a higher energy state, The success was because of a number of factors. The nano-size of the particles meant a greater surface area

‘In Praise ofAir’in situ on theAlfred Denny Building in 2014.

leaving a positively charged “hole”, h+ enabling more pollution-depleting on the Ti atom. Atmospheric oxygen, reactions to occur at once. The poster O2 is reduced by the excited electron was situated facing the sun during to form a superoxide anion, •O2 - and the day and street lighting during the water in the air is oxidised by the night. As the photocatalysis requires “hole” to form hydroxide radicals, light to oxidise the pollutants, the •OH. Nitrous oxides are oxidised by poster was able to remove pollution 24 these molecules to a harmless soluble hours a day. Furthermore, as it faced nitrate, whereas VOCs are oxidised over the concourse it was exposed to to harmless fatty acids which are all a higher amount of car exhaust fumes washed away. as they drove over the busy road. The poem was able to remove the pollution O2 + e- → •O2 - of 20 cars per day throughout the 4 years it was on display. Although now -OH + h+ → •OH the poem is no longer on display and NO2 + •OH → NO3 - + h+ the science behind it remains.

was sold at a charity auction in 2017, 1. https://catalyticpoetry.org/ 2. J.S. Dalton et al, 2002, Environmental Pollution, 120, 115–422.

The team (left to right): SimonArmitage, Joanna Gavins, Prof Tony Ryan & David Walker.