The number of people now living in cities across the globe is as high as it has ever been. With the UN predicting this figure will rise from it’s current level of 55% to almost 70% in the coming decades.
This increase in human density in these areas brings with it a host of potential environmental issues. With pollution being one of the most concerning.
This pollution comes in many forms, from plastic and other waste littering the streets, to toxic chemical substances entering waterways. But perhaps one of the most worrying (in terms of public health) is the issue of air pollution.
What causes air pollution in our cities?
Air pollution from cities is mostly a result of increased numbers of cars and other vehicles burning fossil fuels along with power plants and industrial complexes. In lower-income cities, incineration of solid waste and agricultural waste are also big contributors.
What are the main air pollutants?
An air pollutant doesn’t have to be something that has a direct effect on human health. It simply has to be “a substance in the air that can either have damaging effects on human health or the wider environment”.
As a result of these processes a number of different air pollutants are formed:
- Carbon dioxide (CO2), one of the most well-known greenhouse gases and contributors to climate change
- Nitrogen Oxides, including nitrous oxide (N2O) is another greenhouse gas almost 300 times as potent as CO2
- Sulphur dioxide (SO2), mainly formed by burning coal and leads to the formation of acid rain
- Methane (CH4) and other similar substances mainly formed by rotting organic matter in landfills
- Carbon monoxide (CO), an extremely deadly odorless gas found in exhaust fumes
- Airborne particulates (such as PM2.5) which are solid or liquid particles in the air, including all sorts of things from soot to dust that become suspended in the air. PM2.5 which has hit the headlines recently, refers to any particulate matter with particles measuring less than 2.5 micrometres
- Low level ozone (O3) a secondary air pollutant formed when other gases mix together, posing a risk to human health
According to the World Health Organization (WHO) around 3.8 million premature deaths are attributed to air pollution, around 80% of which are due to heart disease and the other 20% due to other illnesses and cancers.
But as you now know, the effects to the wider environment from air pollutants is also vast, with climate change and acid rain having damaging effects too.
So how can we reduce air pollution levels in our cities? What inventions and innovations are appearing to help reduce this big environmental issue?
1) Vertical Forests
Vertical forests may look like the work of science fiction, but thanks to Italian architect Stefano Boeri the first vertical forest towers, the ‘Bosco Verticale’ were completed in Milan in 2014.
The two towers in Milan are residential towers but with a difference. They are covered in a total of 900 trees, 5,000 shrubs and over 11,000 other plants!
Apart from looking really cool, vertical forests have many potential environmental benefits. The vegetation can absorb carbon dioxide from the air, preventing the gas from causing further greenhouse warming in the atmosphere. But on top of this, plants and trees can act to filter airborne particulates either by intercepting them or absorbing them through pores in the leaf surface.
The effectiveness of different vegetation for absorbing these air pollutants has been found to vary1 but architects such as Stefano Boeri work very carefully to pick the best plants, designing the building for them as well as humans.
Stefano is currently working to design an entire forest city in Liuzhou China, a country heavily impacted by air pollution. According to the architect, the new city will be home to 30,000 people with the new trees absorbing 10,000 tons of CO2 and 57 tons of other air pollutants.
The towers also have the added benefit of providing refuge for birds and insects in cities where habitat is becoming more and more scarce.
2) Smog Free Tower
Dutch designer Daan Roosegaarde created the ‘smog-free project’ as a campaign in the hope of inspiring people to think how to get cleaner air in public spaces.
The smog-free project contained a number of innovations, however, the most striking and memorable was the smog-free tower.
The tower is effectively a giant vacuum cleaner. 7 meters in height, it sits in a public place and sucks in smog, turning it into clean air using patented positive ionization technology.
Although not tackling the source of the problem of air pollution. It could provide localized pockets of clean air in cities, in places such as public parks. And according to Roosegaarde, it cleans 30,000m3 of air per hour using very small amounts of green energy.
The collected smog particles have even been compressed into products such as jewelry.
3) Electric Self-Driving Cars
One of the keys to reducing air pollution levels in our cities will be reducing the number of cars burning fossil fuels. With road transport currently responsible for 30% of airborne particulate emissions in European countries and up to 50% in lower economy countries. In lower-income nations, this is due to older ‘dirtier’ vehicles that have much higher emissions. This is on top of all the greenhouse gas emissions all emitted directly from the vehicle exhausts through evaporation. This air pollution gets much worse when there is congestion. And with cities growing in population, congestion and air pollution levels are also rising rapidly.
One key feature of cities of the future will be electric cars. Electric vehicles not only produce zero direct emissions, but they also have lower lifecycle emissions if the electricity is derived from a renewable source.
It is estimated that electric car sales will continue to go up, with 55% of new vehicle sales expected to be electric by 2040.
Add to this the possibility that these vehicles may soon be ‘self-driving’ we may see even more benefits for the environment. The US Department of Energy claims they will drive more efficiently than humans, decreasing congestion and therefore energy consumption.
This estimate should, of course, be taken with a pinch of salt. Because some other people estimate the arrival of self-driving cars may increase our use of cars (due to us being able to work whilst in them for example). So we will have to wait and see on the overall impact of this innovation. But what we can say is that they should at least reduce some of that toxic smog!
4) Bike and Scooter Sharing Schemes
To prevent the roads of our future cities simply getting clogged up with electric self-driving cars, we will need a mix of different transportation options. This could involve trams, small trains and potentially even electric flying cars!
But with trains and trams confined to specific routes and cities growing so big that walking is even becoming impractical. Other modes of transport are required to prevent people from using cars or taxis which are adding to air pollution.
In recent years many cities across the world have seen bikes and even scooters popping up on street corners almost overnight. Companies such as Mobike and Bird are utilising the latest in mobile and GPS technology to allow anyone with a phone and credit card to hire these vehicles from virtually anywhere in a city and drop them off wherever they are going. Meaning no matter where you are going, there is a clean alternative to cars or taxis.
Another environmental benefit of moving towards a sharing economy, is it reduces the carbon footprint of production. Instead of everybody having to own their own bike or electric scooter a handful is required to be shared amongst many people.
5) Air cleaning buildings
Titanium dioxide is an expensive material to build with (increasing construction costs by 5%) but it has a remarkable property; it reacts with some forms of air pollution in the presence of light to neutralise them.
In 2015 a 13,000 square foot building called the Palazzo Italia in Milan was opened, and it was covered in this material. When opened the people behind the design claimed it could remove 1000 cars worth of air pollution from the air each day!
6) Air purifying clothes
The potential of titanium dioxide to clean up the air has lead to inventors trying to find other uses for it. Designer Helen Storey and polymer chemist Tony Ryan from Sheffield (UK) teamed up to create a laundry detergent which contained the substance. The idea being that when clothes are washed in the detergent they will gain a small amount of the titanium dioxide and turn the wearer of the item into a walking air purifying machine.
However, the invention does rely on mass participation to make a real impact, with each person only neutralizing 5 or 6 grams of nitrogen dioxide (NO2) gas each day. The product is still being refined with a few issues such as the fact it also neutralizes peoples perfume and aftershave, but we will keep an eye on this one.
7) A giant spiders web
Biomimicry is the idea of using inspiration from nature to design solutions to problems we face. Dr Fritz Vollrath from the University of Oxford has been inspired by the ability of spiders webs to catch tiny airborne particulates as they float by, due to their small amount of electrical charge.
Spider webs have amazing properties, being incredibly thin and yet incredibly strong.
Unfortunately (or maybe fortunately), due to their cannibalistic tendencies, spiders can’t be farmed for their silk. But this has led the scientists to hypothesise that perhaps a synthetic version of a spiders web could be useful in capturing dangerous air pollutants, perhaps by placing them over the end of chimneys on polluting factories.
8) Pollution absorbing street furniture
CityTree benches have begun to pop up in cities around Europe. These striking additions look like a section of hedge attached to a bench from a distance, but are actually four-metre-high boards covered in moss.
The Dresden-based creators ‘Green City Solutions’ claim the moss that makes up the vertical garden can do the equivalent work of 275 trees. Sucking air pollutants out of the air which are then digested by bacteria that live within the moss.
The units are built with rainwater collection systems to allow them to stay watered and healthy, keeping maintenance to a minimum. They also contain sensors to gain useful data on air pollution in the surroundings.
They look stunning and I personally would love to see these in cities everywhere. The cost is high at around £17,000 a unit. But the creators advise councils they could claim some of this money back through doubling them up as advertising boards.
9) Algae curtains
Yes I know, these inventions are getting more and more bizarre as the list goes on. But two architects have come up with the idea of using giant algae-filled plastic curtains with the idea of placing them on new buildings as ‘living walls’.
The curtains are comprised of a series of tubes which contain microscopic algae. The idea is that air from ground level will rise up through these tubes containing the algae. Because algae are plants they extract carbon dioxide from the air in the process of photosynthesis just like all other vegetation.
But algae has another advantage. Scientists have found they not only help with carbon dioxide but they also help to break down some of the other air pollutants generated by a city. The designers hope the idea will take off and be used on warehouses and other buildings where appearance isn’t really an important factor.
10) Pollution sensors in street lights
One key to tackling air pollution in cities is building up a better overall picture of where and when air pollution is highest. This allows interventions to be put in place to try and reduce the levels in that area or can advise citizens which areas to avoid.
To get as much data as possible requires as many sensors as possible. One place to put these sensors in order to get high coverage is on street lights, a great option due to their presence in most cities. This is being referred to as ‘hyper-local’ data. Giving accurate levels of air pollution on a street by street basis.
Researchers in Sweden have recently developed tiny nano-sensors that can be mounted in any streetlights and will monitor levels of nitrogen dioxide (NO2). They are so sensitive they can detect levels of NO2 down to parts-per-billion. The aim is that these sensors will be able to detect other air pollutants soon as well.
11) Tiny backpacks for pigeons (to monitor air quality)
Our #PigeonAir patrol are all roosting and we’re signing off for tonight. Goodnight London – see you in the morning! pic.twitter.com/R8MkU1Gz1V
— Pigeon Air Patrol (@PigeonAir) March 14, 2016
I had to include this one because it makes me smile. The innovation isn’t the pigeon, they’ve been around a while. The invention is the tiny pigeon backpacks that have been designed for the pigeons, which contain sensors that can measure several pollutants.
Many say we shouldn’t rely too much on the data captured by these sensors though as tests in the lab revealed they were vulnerable to giving artificial readings. But with these monitoring sensors getting smaller and more accurate all the time maybe pigeon air will take off……sorry.
12) Capturing pollution to use as ink
Air-Ink from Graviky Labs is the first ink to be made entirely from air pollution.
The Labs use their patented KAALINK technology which captures particulates from the air. In fact they claim the unit can capture 99% of particulate matter pollution.
KAALINK is designed to fit diesel generators, car tailpipes or fossil fuel chimney stacks, capturing the pollutant before it can get into the ambient air. This particulate matter is stored in the unit and can then be used safely as ink in various art projects.
Just 25 hours of driving can produce 1.5 litres of ink! This is cool, but also shows you just how much particulate matter is leaving our car exhausts every day!
13) Clean cookstoves
It isn’t just outdoor air pollution that is damaging people’s health. Indoor air pollution is also a big concern. And this concern is highest in less economically developed countries, where the use of cookstoves or open fires indoors is still very common. It is still one of the top five health risks in developing countries.
The Global Alliance for Clean Cookstoves is led by the United Nations Foundation and hopes to bring clean cookstoves to households, saving lives, empowering women and tackling other environmental issues.
Open fires and old fashioned cookstoves are extremely inefficient with only a small amount of the energy generated from burning the fuel actually going into cooking the food. So the main way that clean cookstoves work is by being much more efficient, producing much less smoke in the process.
Fuel is raised up off the ground on a metal grate, allowing a flow of air underneath into a well-insulated chamber. This means much more of the energy from the fuel is used for cooking. This can then be attached to a small chimney which maintains the air flow and stops the dangerous air pollutants getting trapped in the home.
The key, of course, is to create a market where these stoves are affordable and with prices now down to around $25 charities can afford to donate them to many areas.
14) Smart parking and traffic management
As I’ve mentioned already, cars driving around cities and stuck in congestion are major contributors to air pollution. So before all cars are electric and automated and can do all the thinking for us. We must make the most of the technology we have now and make traffic move around cities more efficiently.
With parking spaces at a premium in cities, this can leave many cars circling around the block or idling on the side of the road waiting for a parking space to appear.
This has been trialed in San Francisco, with the SFPark initiative helping drivers find vacant spaces. Since launching the initiative, the time taken to find a space decreased by 43%, resulting in estimated emission decreases of 30% whilst also decreasing overall traffic volume on the streets.
15) Giant smog sprinklers
Not the most cutting-edge innovation on this list but it does a job. In China, Yu Shaocai proposed the idea of using giant water sprinklers to spray water into the air. This water acts in the same way that raindrops would; by attaching to particles of particulate matter in the smog, causing them to fall to the ground in a process known as ‘wet deposition’.
The idea is to attach the giant sprinklers to the tops of buildings and skyscrapers in the middle of polluted cities.
The jury is still out on the environmental impact of all the water required to perform this though. It feels like very much a last gasp effort to remove pollution (that’s why it’s near the bottom of this list).
16) Smog busting drones
As well as using water vapour to tackle air pollution and smog. The Chinese government also wants to use certain chemicals to ‘freeze’ air pollution particles making them fall to the ground.
But they have to get these chemicals into the atmosphere where the pollutants are and so to do this they have come up with the idea of a ‘smog busting drone’.
The state-owned aviation industry has developed a drone that is attached to a parachute. The idea of using automated drones is because they are not only much cheaper than using piloted aircraft to carry out the operation, but they are also much safer, with visibility in some of the worst polluted areas being very bad indeed.
The drones have started testing in some of the most heavily polluted areas, such as around airports where air pollution is so bad pilots now have to carry out tests for ‘blind landings’!
17) Air filtering bus
At the end of last year, UK transport company Go-Ahead launched a new bus. But this wasn’t any old bus. It was a special bus fitted with a rooftop filter that filters the air as it drives along.
The filter system on the roof works by trapping particulate matter as the bus drives around and then blowing out clean air behind it.
The company want to promote the increased use of buses as not just a solution to congestion by reducing the need for as many cars. But also as a mobile filter doubling the benefits.
As much as we love innovation and disruption on this blog, innovative ways to reduce air pollution are of course only part of the solution.
For us to see a significant reduction in air pollution in our cities we need to be looking at measures such as banning most cars to reduce congestion or using renewable energy rather than burning coals and other fossil fuels nearby.
But whilst we aim to tackle pollution at source, there is nothing wrong with a bit of disruptive innovation to help us breath cleaner air in the meantime.
1 L. Chen, C. Liu, R.Zou, M.Yang, Z.Zhang, Environ. Pollut. 208, 198 (2016).