As part of the BBC's So I Can Breathe series, a week of stories exploring some of the different ways the world is seeking to reduce air pollution, people have been sharing their tips on how to improve the air around them.
For Phoebe, Joylen and Verity, from London, the answer is to stop cutting down trees.
Students at 50 London schools breathe air that exceeds legal pollution limits.
"Toxic air audits" have been announced by the mayor of London to combat the problem.
According to the US Forest Service, trees typically reduce urban air pollution by only up to 1%, but even this can have significant health benefits.
Areej and her mother also want to plant trees in urban areas of Damascus to improve air quality.
Wood-burning stoves are a cause of high indoor air pollution levels which have been linked to four million premature deaths annually, according to the World Health Organization.
Adboulie Sey thinks they should be banned from Gambia and solar energy promoted instead.
Africa's new breed of solar energy entrepreneurs
A tax on wood stoves is another solution, suggested by Karen Baines on Twitter.
Improving how we travel is a common desire.
Swapping driving for cycling can reduce the number of vehicles on the road emitting pollutants such as nitrogen dioxide.
Clare Rogers tweeted this picture of her and her daughter in Enfield.
Robert Singleton suggests a ban on diesel powered vehicles would go some way to reducing pollution.
Girl guides helping to clean Ghana's air pollution problem
Improved public transport is also proposed by Maria Innes in Buenos Aires, and echoed by Oscar Soria, in New York.
Mike Hall thinks government schemes to support people buying hybrid or electric cars is one way to encourage more environmentally friendly transport.
And Pablo Nieto Gonzalez in San Sebastian, Spain, wants emissions from ships to be cut.
A week of coverage by BBC News examining possible solutions to the problems caused by air pollution.

Dorset Police said officers had restrained the man, who was reported acting erratically in Poole on Tuesday.
The man suffered a medical episode while with the officers, who performed CPR while waiting for an ambulance.
He was taken to Poole Hospital but his condition deteriorated and he died on Wednesday morning, police said. His next of kin have been told.
Police have referred the death to the Independent Police Complaints Commission (IPCC).
A statement from the force said officers were called at 16:12 and 16:19 BST amid concern for the man's welfare.
The statement said: "When officers arrived, a man matching the description was found on The Avenue. He was restrained while officers assessed the situation.
"While with officers he suffered a medical emergency. The ambulance service was requested to attend and officers performed CPR while awaiting their arrival.
"The man was taken to Poole Hospital for further treatment. Sadly, his condition deteriorated and he died in hospital this morning."

Sixty teams submitted plans for Clandon Park House in Surrey, which was reduced to a charred shell in 2015.
The National Trust has announced a shortlist of six teams, as well as the names of those on the jury, which will make a final decision after a public consultation over the summer.
Building work is expected to begin by early 2019, the National Trust said.
The National Trust said it wanted plans to combine restoring state rooms in the Grade I-listed building with new galleries and visitor spaces.
Sandy Nairne, who is chairman of the jury, said: "We received an excellent set of submissions, offering many fascinating collaborations and partnerships.
"The shortlist represents a collection of great talent from the UK and abroad.
"The teams that were selected had thoroughly analysed the conservation issues and design opportunities, and proposed thoughtful and creative approaches."
The six shortlisted teams will create concept designs which will go on public display in the late summer, The winning team is due to be announced in early autumn, the National Trust said.
The trust said the high-profile project had a Â£30m construction value.
From Ghana to Argentina and London, air pollution is a problem that people want to do something about.
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A man who police had been called to help after he was seen wandering among traffic has died in hospital.
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The National Trust has announced the design teams shortlisted to rebuild an 18th Century mansion destroyed by fire.