Oxides of nitrogen are harmful components of air pollution, contributing to the formation of ground-level ozone and fine particulate pollution that cause respiratory issues in humans.
A common mineral, research shows, can neutralise the pollutants when added to projects in the built environment.
Nitrogen oxide (NO) and nitrogen dioxide (NO2), together referred to as oxides of nitrogen or NOx, are components of air pollution produced by combustion of fossil fuels in vehicles, power plants, and off-road equipment. Australia’s Department of the Environment lists electricity production and motor vehicles as the largest NOx polluters, at 36 per cent and 26 per cent of emissions, respectively.
Titanium dioxide, a naturally occurring mineral, is used industrially, often as a white pigment. When exposed to NOx molecules in the presence of ultraviolet radiation (sunlight), titanium oxide breaks down NOx molecules into nitrates. After the chemical reaction, the nitrates are washed away in the rain.
Chemist Luigi Cassar and Italian cement company Italcementi formulated a cement mixture for the Jubilee Church in Rome after architect Richard Meier specified a white cement.
“During the construction of the church in Rome, we discovered that the air around the church was actually less polluted than before," Cassar noted. "The titanium dioxide contained in our cement caused the harmful substances in the air to oxidize faster.”
According to Italcementi, titanium dioxide can be used in mortar, plaster, and paint. They call their recipe TX Active, and say a plaster coating for a five-storey building would cost 15 per cent more than a standard finish, but air pollution would decrease by 20 per cent. Used on a city-wide scale, covering 15 per cent of visible surfaces with their product, Italcementi claims pollution reductions of up to 50 per cent are possible.
Before marketing the product, the company performed extensive testing in both simulations and real-world situations. The company’s report provides examples of both laboratory testing and real-world, on-site testing.
TX Active was recently awarded the second place Popular Prize at the 2014 European Inventor Awards, and chemist and TX Active developer Luigi Cassar was nominated for the European Inventor Award.
In addition to cement, titanium dioxide can be added to roofing materials. Danish firm Icopal produces a roofing membrane called Noxite.
According to the company, the membrane’s granules receive a coating of titanium dioxide that will neutralize NOx pollution for the life of the roof. The company says each square metre of Noxite roof will purify 50,000 cubic metres of air per year, which is roughly equivalent to the amount of air used by 12 people per year. A 100 square metre roof will remove the amount of NOx produced by an average car travelling approximately 16,000 kilometres.
The company’s claims are supported by independent research. The French Centre National de la Recherche Scientifique (CNRS) in 2009 awarded Noxite a “Green Pass Innovation” for its photocatalytic characteristics.
Icopal also commissioned the British Board of Agrément (BBA) to evaluate three separate reports from independent testing agencies. The BBA concluded that the Noxite material has “a significant depolluting capacity when added as a mineral finish to waterproofing membranes.”
The BBA summarised the reports as follows:
- UL Environmental estimated that, over a 20-year period, between 417 grams and 4,143 grams of nitrogen oxides per square metre of roof can be absorbed and degraded from the atmosphere.
- The Centre Scientifique et Technique du Batiment (CSTB) reported a depolluting level of approximately 90 per cent in membranes two months after installation.
- TNO estimated an effective deposition rate of 0.08 cm.s-1 and 0.10 cm.s-1 as measured in laboratory tests and in-use conditions respectively.