Smog and air pollution have become one of the most severe issues facing the world today, causing reduced visibility and breathing difficulty in urban areas.
Smog is generally defined as a mixture of gases, water vapor, and dust. The most common type of smog is known as photochemical smog, the production of which occurs from the reaction of sunlight with nitrogen oxides (NOx) and, at a minimum, one Volatile Organic Compound (VOC) in the atmosphere. Car exhausts, industrial factories, and coal power plants are the primary sources of NOx, while VOCs come from paints, gasoline, and cleaning solutions.
About 134 million Americans reside in locations where smog is present, and U.S. News reported that 100,000 people died from complications due to air pollution in 2019. The World Health Organization (WHO) has found that 4.2 million deaths per year are a result of diseases caused by air pollution, including strokes, lung cancer, and other respiratory illnesses.
Applying Engineering Tactics to Combat Smog
Poor air quality and its effects on the planet have warranted an in-depth evaluation of engineering methods that can be used in construction to enhance the quality of the surrounding air. Approximately 91% of the world’s population is exposed to air quality levels that exceed WHO’s recommendations.
However, researchers have found that introducing Titanium Dioxide (TiO2), a naturally occurring mineral, into building solutions has yielded some positive results in reducing smog levels where it is implemented. TiO2 promotes photocatalytic reactions. It acts as a catalyst to produce a chemical reaction when exposed to ultraviolet light, which reduces the concentration of pollutants in the air.
Engineers in Japan first used cement and tiles made from TiO2 in the 1990s to breakdown NOx chemicals. In 2003, an estimated 5,000 buildings in Japan were constructed using TiO2 based tiles. Italy’s experimentation with catalytic materials first occurred in 2002, when 75,350 square feet of the road surface was covered with catalytic cement. By doing this, concentrations of NOx were reportedly reduced by 60% at the street level.
In March 2004, Ecopaint, a clear paint embedded with nanoparticles of titanium dioxide, hit shelves in Europe as a solution to urban noxious gases. Experiments and trials have continued to assess the positive impacts of TiO2 on the environment. A two-year trial of a TiO2 paint produced by Cristal, in London, showed that pollutants were reduced by approximately 65%, in the vicinity of the paint application.
Alcoa would later get involved in the development of smog reducing panels; in 2011 the firm launched its Reynobond architectural panels with EcoClean to neutralize pollutants when used on building facades; Alcoa estimated that 10,764 square feet of this material could offset NOx emissions from four vehicles.
The Perfect Solution to Pollution?
Applications of TiO2 have continued to shape the landscape of building construction; Projects in Mexico and Milan are integrating TiO2 coated tiles with air cleansing abilities. In 2019, a team of engineers combined graphene and TiO2 nanoparticles to form a catalyst powered by solar energy.
But despite advancements in the use of TiO2, several studies indicate that there is a downside to using the material. Scientists in China and France have studied the decomposition of TiO2 paints and found that during the breaking down of pollutants, other toxic compounds are released into the atmosphere. The Chinese Academy of Sciences concluded that significant amounts of VOCs such as the carcinogenic formaldehyde were produced during degradation.
Because of these concerns, there needs to be further understanding of the pros and cons associated with the use of TiO2 in buildings. Investigation and monitoring are critical before TiO2 becomes more widely implemented as a means of filtering smog.