People in cities like London, Cardiff, Manchester, Bristol, Birmingham and Bristol may notice a new series of Volkswagen ads being painted on exterior walls of buildings. Is it possible that the air seems just a little fresher when walking by the new ads?

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A streetscape in London with a large painted VW ad on the side of a building to the left.

When Volkswagen announced it was using a sci-fi-sounding, smog-eating paint on its U.K. billboards, the reaction was mixed. Is this notoriously eco-unfriendly company turning over a new leaf? Do they really care now? And does the paint really work, or does it cause more harm than good?

Related: This “super plant” can actually absorb air pollution

Past scandals

Let’s time travel back to the “diesel dupe” of 2015. VW was busted big time when the public found out about some shady software in diesel engines that came to be known as the “defeat device.” This gizmo detected when the car was being tested and suddenly was on its best behavior. The engine ran below its normal level during the test. But post-exam, it cranked up and spewed up to 40 times above the amount of nitrogen oxide pollutants allowed by U.S. law.

When caught, VW leaders were contrite. They admitted they’d screwed up and vowed to win back public trust. They launched an internal inquiry and set aside billions to cover the cost of recalling millions of cars worldwide. And now, the paint used in their advertising eats smog.

A large painted VW ad on the side of a building, reading "It's not going to make a big impact."

Meet the paint

A couple of different projects have been working on smog-eating paint, including ENERPAINT and Airlite. The idea behind ENERPAINT is to refurbish old historical houses, which are usually energy inefficient. VW is using Airlite paint for its ad campaigns. 

“The purpose of Airlite was to create something that makes a difference to human health and well-being in the built environment,” said Chris Leighton, VP of sales and marketing at AM Technology, the company responsible for Airlite paint. In addition to eating smog, Airlite allegedly repels dirt, removes bad odors and kills mold, viruses and bacteria. “The basic principle is photocatalysis, a reaction that happens in the earth’s atmosphere,” said Leighton. This natural reaction breaks down pollutants.

The early experiments were promising. In 2007, Rome’s Traforo Umberto I tunnel was thoroughly cleaned before getting a coat of the smog-eating paint. “Pollution levels reduced in the tunnel after the renovation,” said Leighton. A month after the tunnel’s makeover, the nitrogen oxide levels dropped 20% in the center of the tunnel. Since then, schools, offices, airports, hospitals and homes have all been painted with Airlite. Street artists even created Europe’s first smog-eating mural on a seven-story building in Rome.

The paint is also good for cooling indoor spaces during hot weather. When the sun hits the building, the heat reflects off, saving on air conditioning emissions and bills.

How does paint eat smog?

If you’re still wondering how it works, read on. According to manufacturer claims, the titanium dioxide crystals in Airlite break down chemical substances when the paint is exposed to humidity and light. Sunlight stimulates titanium dioxide. Electrons are released to water vapor molecules, transforming them into free radicals which react with pollutants like NOx and change them into harmless substances. About 20% of NOx in the air could be neutralized by painted surfaces.

Instead of using the volatile organic compounds generally found in paint, Airlite started with a calcium base — a byproduct from an Italian marble processing site. To use the paint — which comes in powdered form — you just mix it with water.

A large painted VW ad on the side of a building. A blurry figure walks past on the street in front of the building.

Mixed results

It sounds awesome! But is it? Some scientists have their doubts, even saying the paint can do more harm than good. A study published in 2017 in Environmental Science: Nano concluded that while photocatalytic paints effectively decompose some pollutants, they unfortunately generate and release different toxic compounds.

“Photocatalytic paints are an excellent example of a treatment technology using sustainable energy as they only require sunlight or ambient lighting to work,” said Delphine Truffier-Boutry from Grenoble Alps University in France, who worked on the study. “However, the issues presented here challenge the usefulness of the titanium dioxide-based photocatalytic paints as a remediation technology to improve urban and indoor air quality. Lots of effort is needed to make this technology viable for air quality improvement.”

The scientists tested the titanium dioxide nanoparticles’ effectiveness at eliminating volatile organic compounds from the air by introducing xylene. Sure enough, the paint eliminated the xylene. But unfortunately, it released other toxic nanoparticles, including formaldehyde. More study is warranted, especially before you paint the inside of your house with this stuff.

A large painted VW ad on the side of a building.

Other VW eco measures

Despite the jury still being out on smog-eating paint, Volkswagen seems sincere in its new eco-efforts. They’ve worked on offsetting their vehicle delivery emissions by supporting climate protection projects, such as Borneo reforestation. The automaker has also beefed up its charging station network for Great Britain’s electric vehicles by partnering with Tesco. Now, more than 250 Tescos are equipped with Pod Point charging stations.

The VW campaign is also employing artists. It takes about three to six days for an artist to paint the VW ads, which will likely be on display in U.K. cities for roughly a month.

Via BBC, Clean Technica, Horizon and Chemistry World