City tree

Breathe easy: inspired ideas for purer air in cities

We may have to wait years for all heavily polluting vehicles to be scrapped, so technology that helps clean the air - especially in our cities - is a good investment. Here are six innovative ideas to help us breathe better.

City vacuum cleaner

A giant vacuum cleaner developed by Dutch company Envinity Group can remove particulate pollution from the air within a 7km-high column with a 300m radius. The firm says the technology, unveiled at a fair in Amsterdam last October, can purify 80,000 cubic metres of air in one hour, filtering out 100 per cent of fine particles (2.5µm in diameter) and 95 per cent of ultra-fine particles (less than 0.1µm in diameter).


The ability to demonstrably remove ultra-fine particles is a major step forward, the inventors say. Unlike the larger PM10 and PM2.5, concentrations of ultra-fine particles are not regularly measured, although evidence suggests they might be by far the most harmful. Ultra-fine particles, which are 25 times smaller in diameter than a human hair, are the likeliest to penetrate deep into the lungs and cross into the bloodstream.

The Envinity Group inventors envisage that city councils in future could install the firm’s 8m-long air-cleaning cannons on top of buildings and use them to relieve the choking residents.

Smog Free Tower

Dubbed the ‘world’s largest air-purifier’, the 7m-high Smog Free Tower, built by Dutch designer and innovator Daan Roosegaarde and his team, was put to the test in Beijing in late 2016. In development since 2013, the technology removes up to 75 per cent of PM2.5 and PM10 particles using a patented ozone-free pollution-scrubbing system.


Purifying 30,000 cubic metres of air per hour, the Smog Free Tower created a circular bubble of fresh air for inhabitants of the notoriously polluted Chinese capital to enjoy. Beijing authorities said air in the vicinity of the tower was 55 per cent cleaner during the 41-day experiment at Beijing’s 751 D.Park. The system, running on renewable energy, cleaned a total of 30 million cubic metres of air during the trial.

Roosegaarde used dust captured by the system to create a collection of limited edition jewellery. One Smog Free Ring contains compressed particles from 1,000 cubic metres of air.

The technology, which was first piloted in Rotterdam, will now continue to other Chinese cities.

City Tree

City Tree [pictured above] by Berlin-based start-up Green City Solutions, is made up of special moss cultures that collect particulate matter on their leaves and is cradled by an IoT frame that ensures optimum growing conditions.


“Mosses, unlike other plants, don’t take nutrients from the ground through their roots but directly from the air,” says Liang Wu, CIO and co-founder of Green City Solutions. “The moss cultures that we use can do this extraordinarily well because they are like a sponge.”

The moss plants create an electrostatic charge that draws pollution particles toward the leaves.

Compared to normal trees, the City Tree has multiple advantages. The moss is green all-year-round and has a much larger leaf area than trees. Green City Solutions estimates that a single City Tree can capture as much dust as 275 trees. Planting 100 City Trees within 10km2 would prevent a polluted district in central Berlin from breaching annual limits for PM2.5 and reduce carbon dioxide emissions by 240 tonnes per year.

The major task for the company was to ensure good growing conditions for the sensitive plants in the city environment. “Mosses only grow where other plants can’t,” Wu explains. “They need more shade, they need acidic ground environment.” The smart internet-connected structure that houses the plants constantly monitors their state and regulates water supply and temperature.

A few City Trees have already been planted in Hong Kong, Paris, Oslo, Berlin and Hannover. To make a measurable difference to air quality, a City Tree would have to be planted about every 100m along a busy road. Green City Solutions hopes to start larger-scale trials later this year.

Storm-inspired city air cleaner

A little-known UK-based company, Vivex Engineering, has developed a Modular City Air Cleaner (MCAC) inspired by the atmosphere-purifying effects of rain and thunderstorms. The firm, which makes cold plasma air purification systems for factories, designed a solution that sucks air through a high-voltage high-frequency electric field. The electric field produces lightning-like electrical discharges, ionising the air inside the module. The lightning changes the chemical composition of pollutants present in the air and aggregates small particles into larger clusters.


A stream of water subsequently washes away pollutants, just like in a summer rainstorm. The technology also kills bacteria and viruses present in the air.

Vivex Engineering says one standard MCAC unit clears the air within a 25m-high column with an 80-metre radius. Purifying one cubic metre of air requires approximately a tenth of a watt of electrical power. The environmentally friendly technology could be enhanced by integrating a solar panel into units exposed to direct sunlight. In tests, the technology removed 50 per cent of dust particles on average and 55 per cent of nitrogen oxides.

Air pollution ink

Even air pollution can be turned into something useful, researchers from Massachusetts Institute of Technology have found. First they developed a device called KAALINK that can be retrofitted into old vehicles to capture soot produced by the combustion engine. The MIT team collects dust and turns it into high-quality ink that can be used in pens, markers or for screen printing. Forty-five minutes of driving produces enough soot for 30ml of AIR-INK, which the MIT spin-off Graviky Labs started selling on Kickstarter.


Pollution collected by the KAALINK device undergoes a complex chemical treatment that removes all heavy metals and carcinogens. What remains is a purified carbon-rich pigment. Graviky Labs also plans to start manufacturing pollution-based oil paints, fabric paints and outdoor paints.

Paint eats air pollution

Titanium dioxide, used in self-cleaning paints and varnishes, can also remove nitrogen oxide pollution from the air. A couple of years ago, a team of students from the University of California Riverside developed roof tiles using the pigment that can allegedly neutralise almost 18,000km-worth of driving emissions in a year if installed on a roof of an average-sized residential property.


UV light, or sunlight, illuminating a surface coated with titanium dioxide, initiates a chemical reaction that decomposes everything on and near the surface into CO2 and water. This reaction was first described in the early 1970s and has since been harnessed in various applications including self-cleaning windows and mirrors.

The air-pollution-removing capabilities of titanium dioxide have previously been tested in Japan.

The titanium dioxide concoction of the California University team could remove 21 tonnes of nitrogen oxide daily if one million roofs were covered with it. The cost of the coating per roof could be as low as $5. In laboratory tests, the titanium-dioxide-coated tiles removed up to 97 per cent of the nitrogen oxides present in the surrounding atmosphere.

Read more about Tereza’s experience as part of a Kings College London experiment to analyse the concentrations of dangerous air-borne particles that London’s residents inhale on a daily basis.

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