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Creative Air Purification Solutions for Cleaning up Polluted Cities

March 02, 2019 by Sam Holland

Over 90% of the population is breathing in air that exceeds the World Health Organization’s standards, the authority says. But at least every smoggy, CO2-filled cloud has a silver lining: there are many engineers out there bringing breakthrough air cleaners to the urban landscape.

Two key parts of combating the pollution in our cities are 1) to address transport, particularly eco-friendly vehicles, 2) and, naturally, urban architecture itself. With China working hard to remedy that fact that it's the world’s most air-polluting country, its cities are a vital place to start when considering the importance of both cleaner travel and construction.

With this in mind, let’s ‘clear the air’ with a look at China’s Beijing-based smog-cleaning bicycle prototype plus, of course, its giant purification tower in the city of Xi-an.

The Smog Free Bicycles Initiative

Studio Roosegaarde, a Dutch eco-friendly design lab, have devised a transport solution that not only helps in the removal of unclean air, but it also encourages the avoidance of it altogether. It does this by introducing a clean-smog-on-the-go peripheral to a vehicle that of course releases no such pollutant.

Image courtesy of Studio Roosegaarde.

First imagined by the eponymous Dutch artist and inventor Daan Roosegaarde, the Smog Free Bicycle—a part of the Smog Free Project (SFP)—is planned for commercialisation with the help of Beijing-based bicycle sharing company Ofo (although sadly, as discussed later, the latter’s financial future has since proved uncertain).

It works through a small plug-in device which is mounted on the front of the bike, to “inhale polluted air, clean it, and give clean air to the cyclist”, as Roosegaarde’s website explains.

The prototype module has an inbuilt carbon filter that makes this possible, which facilitates a staple part of traditional air purification devices, such as those seen in many domestic air cleaners: positive ionisation. In other words, the device charges the incoming smog, rendering its particulates static and therefore able to be contained in the carbon screen (although thanks to the degradation issues surrounding the ionisation ‘black wall effect’, this will at least call for filter cleaning every month or so).

Image courtesy of Bigstock.

The result of the process, something constantly being powered by pedalling alone, is that only the remaining filtered air is left to exit the purifier. This means that wherever its future users ride, they will be rewarded with a sort of anti-smog bubble for choosing such an eco-friendly choice of transport.

Plus, of course, they will also be rewarded with the knowledge that they are making a difference to city life which, in turn, could encourage a future where cycling is even more ‘green’ than we consider it today.

It goes without saying at this point that such an area of the SFP marks one of the initiative’s more humble approaches to city air cleansing. As Roosegaarde himself told “I don’t have the whole answer, but this is what I can do to improve [cities]. I can design and I can engineer”.

But questions of modesty aside, and even in spite of the project’s kryptonite touched on above (collectively: ionisation filters conveniently charge particles rather than outright sanitise them, and vandals and thieves have sadly threatened its potential partner Ofo’s, longevity). Roosegaarde’s success may be in his message rather than his results alone. What could promote anti-pollution attitudes more than cycling through a clean cloud of air, after all?

Similarly, another one of the Dutch inventor’s SFP entries, the Smog Free Tower, may have limitations in its ionisation process, plus the fact (discussed below) that its once-world-beating 7m height has since been dwarfed after its introduction in 2015, it continues to stand proud as an eco-friendly statement. And of course, it will always be the first of its kind.

Image courtesy of Wikimedia Commons.

But now let’s now see why it’s the first of its kind: the below shows that all of the said brilliance from Roosegaarde is proving just the start in the way of breakthrough air purification...

Xi’an’s Air Purification Tower

In Central China’s city of Xi’an stands a record-breaking 100m building that reduces smog through a very efficient form of absorption and filtration. It’s immediately surrounded by a collection of greenhouses (that would altogether cover roughly half a football pitch), and their job is to pool China’s surrounding polluted air, before transferring the toxic gases into the bottom of the tower.

From there, its solar-powered infrastructure ensures the offending air is safely risen by heat to the top of the building while being filtered every layer of the way. Only then is the once-toxic air released back into the atmosphere.

The end result is that Xi’an is now enjoying all of the following benefits and more:

  • Up to 10km2 of purified air that encompasses the tower for as long as it’s active;
  • A solar-powered system so efficient that almost no electrical power is required during daylight hours—plus, the greenhouses’ well-insulated coating ensures continued efficiency even in winter.
  • Eyewitness claims of a vast improvement (at least one person was grateful for the cleaner air without even knowing that they had the tower to thank!)

The last point is particularly promising, as it means that the tower has not just proved a success on the T&M front, but to the very human senses as well.

Image courtesy of Bigstock.

To clarify the former aspect, this was established by the Institute of Earth Environment at the Chinese Academy of Sciences, where air samples were taken and then measured at a microscopic level: the result was particulate matter at less than 2.5 micrometres in diameter (or PM2.5 for short—‘PM’ being a typical air quality unit of measurement).

The PM2.5 readings of the tower’s surrounding air showed a 15% drop since the purifier’s completion in May 2016. So, all in all, the above points mean that not only are citizens breathing in less toxicity, they are benefiting from a visible improvement, too. Better still, such accomplishments have opened the door for even bigger projects, such as a new, already-patented version of the tower that could stand 5 times taller than the one mentioned here.

This could facilitate 30km2 of filtered air, a feat that could see the detoxification of a small city’s worth of pollution (for context, the bustling UK city of Lincoln is 35.69km2). So while the existence of urban toxicity certainly remains a problem, at least the present and future of air purifiers are a ‘breath of fresh air’. Indeed, the curative measures—be they transport-based, architectural, or anything in-between—are set to improve city atmospheres in the years to come.

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