The worst places in the world for air pollution have changed over the years. In the 20th century, London’s coal-induced smogs caused problems; later, Los Angeles’s snagged up traffic caused petroleum exhaust fumes to pump into the air. For most of the 21st century, Beijing has dominated headlines for its high particulate matter, while now Delhi and other Indian cities are coming under the microscope. In 2018, the WHO released its list of the world’s 20 most polluted cities: 14 of them were in India.

But air quality isn’t a problem for “emerging economies” or cities — it’s a problem that affects people. Nine in 10 of the world’s population lives in a place that exceeds air quality guidelines set by the WHO. The issue is exacerbated by the way we live, with fewer people each year working and living in agricultural societies. Some think we’ve reached a point of no return — but governments, politicians and researchers have recognised the issue, and are taking action.

As a result, major innovations are being made in city planning, transport infrastructure and cutting-edge technology solutions to try and fight the rise of pollutants in our air. Here’s just a handful of ways our towns and cities — as well as the buildings and monuments around them — are changing to tackle the problem.

01 — Airlite paint, Absolut Street Trees, Mexico
Graffiti and street art are often maligned for ruining a city’s environment, but in Mexico City, a 35-metre high tree emblazoned on the side of a building on the city’s Paseo de la Reforma boulevard is doing good in more than one way. The mural, painted by Spanish collective Boa Mistura, uses Airlite paint, which uses chemical reactions to clean the air using a process that’s similar to photosynthesis. When the sun shines on the mural, chemicals in the paint oxygenate the air nearby. Various murals dotted around Mexico City using the paint are thought to cancel out the exhaust fumes of 60,000 vehicles every year.

02 — Photo.Synth.Etica sheet
The product of Claudia Pasquero and Marco Poletto from architectural and urban design lab EcoLogicStudio, Photo.Synth.Etica is an extra-large piece of plastic sheeting that, when draped over a building, claims to clean the air around it. The sheet is dotted with vein-like tubes filled with liquid that reportedly uses micro algae to sequester carbon. Photo.Synth.Etica’s makers say that it captures a kilogram of carbon dioxide every day — approximately the same amount that would be cleaned by a small cluster of 20 large trees. The sheet was first hung over a building in Dublin and, if it proves successful, could be a simple way to adapt existing buildings to make them more eco-friendly.

03 — ElectReon recharging smart Road in Sweden
Many cities, including London, are introducing ultra-low emissions zones, barring petrol and diesel vehicles from certain highly populated parts of the city to reduce emissions. Amsterdam wants to ban petrol and diesel cars and motorbikes by 2030 under its Clean Air Action plan. And in their place, electric vehicles are taking to the streets. But installing charging points is a challenge. Sweden has a solution: the ElectReon recharging road near Stockholm has two rail tracks embedded in the middle of the lane, into which a moveable arm at the bottom of a vehicle can dock, recharging electric vehicles as you drive.

04 — Biosolar Leaf
We all know the power of trees to naturally clean the environment, but planting them and waiting for them to grow not only takes time, but also space. Researchers at Imperial College London and biotech startup, Arborea, have managed to crunch down the air cleaning powers of trees into a smaller package — the Biosolar Leaf. Harnessing the power of algae, the leaf supposedly does the work of 100 trees for the surface area of just one. Tiles peppered with microscopic plants such as microalgae and phytoplankton can be installed on rooftops, naturally cleaning the air around us.

05 — Xi’an air cleaning tower
A 100-metre-high tower in Xi’an, in China’s Shaanxi province, helps clean air of smog in a 10 square-kilometre radius. The tower sucks in air and pushes it down to the greenhouses around its base. There the air heats up and rises back up the tower, passing through cleaning filters on the way. Levels of PM2.5 dropped by up to 15 per cent when passed through the tower. The construction also manages to clean up air at scale — around 10 million cubic metres a day at peak.

It’s not just issues at street level that are causing sleepless nights for scientists, politicians and the rest of us: pollution can seep into buildings through open windows, doors and air conditioning systems. It’s a pervasive problem, indoors and out.

And indoor air pollution can be significantly worse than conditions outdoors. Indoor pollutants can be found at two to five times greater levels than outdoors according to the US Environmental Protection Agency — and at its peak can be up to 100 times worse than the open air.

We often think that being indoors shields us from harm, which isn’t always the case. A 2015 report by real estate company JLL and environmental consultancy Pure Living found that 90 per cent of office buildings in China’s capital didn’t substantively reduce pollutants in the air indoors — even though it needed to. Just by cleaning our indoor environments’ air offers a substantial opportunity to tackle our air quality problem generally.

Sometimes this can take the form of technological solutions developed in laboratories specifically designed to tamp down the levels of harmful pollutants. Other times it’s harnessing the power of nature that has kept our planet’s air relatively clean for millennia. And occasionally, it requires small shifts in how we live, work and play — and once in a while, opening a door or cracking open a window to let the air in and out.

01 — Silver birch trees
Despite all the technological innovations, sometimes the original solution is the best. Planting silver birch trees along the fringes of some of our busiest roads can cut the amount of pollution inside homes in an area by half, according to scientists at Lancaster University, who planted 24 saplings alongside a major arterial road in England. Artificial attempts to replicate the impressive greening ability of trees go some way to damping down the worst pollutants, but it seems nature’s original solution is still the best.

02 — Hypoallergenic Cats
Already, two companies in the US say they plan to edit the genes of cats so that they don’t cause allergies. Contrary to popular belief, humans aren’t actually allergic to animal hair. In fact, most pet allergies are actually just a bodily reaction to dander — which is a secretion in the animal’s sweat and saliva left on fur during the grooming process. As a result, companies like Indoor Biotechnologies and Felix Pets each filed patents experimenting with pet DNA. Controversial CRISPR gene therapy techniques could also potentially alter dander secretions to ensure they don’t cause a reaction.

03 — Bionic chandelier
Artist Julian Melchiorri’s bionic chandelier does two things in one: the light helps illuminate any room in which it is installed, while also triggering photosynthesis in the tiny microalgae positioned on the numerous green petals that make up the structure of the chandelier. Those microalgae then help clean up the pollutants from the air around the chandelier. The item is part of the permanent collection in London’s Victoria & Albert Museum, but it could pave the way for more mainstream adoption of this technology in offices and public spaces.

04 — Ventilation
It sounds counterintuitive: air pollution is often seen as an outdoor problem, so how can letting outdoor air indoors help matters? But having no air movement in a building by hermetically sealing doors and windows can cause problems, as the concentration of pollutants in the air grows by simply breathing. So, making sure there’s air flow through a building, including opening the window, allows some of those more harmful pollutants to leak out and new, fresher air to come in. Cracking a window is a method approved by the US Environmental Protection Agency.

05 — Dyson Purifier
The new Dyson Pure Cool™ purifying fans — in a large tower format for floor placement, and a small desk format for worktops and floors — automatically purify the whole room properly, capturing gases and 99.95% of ultrafine particles as small as 0.1 microns. LCD displays also show real-time pollutants.