A new report from UNICEF has found that around 300 million children – nearly one in seven on the planet – are living in parts of the world where levels of outdoor pollution are at their most toxic.
The report, Clear the Air for Children, used satellite imagery of outdoor air pollution to calculate that 300 million children were living in areas where levels exceeded "international guidelines by at least six times."
UNICEF added that roughly two billion children were living in parts of the world where outdoor air pollution breached the World Health Organization's (WHO) minimum air quality guidelines.
"Air pollution is a major contributing factor in the deaths of around 600,000 children under five every year – and it threatens the lives and futures of millions more every day," Anthony Lake, executive director of UNICEF, said in a news release.
"Pollutants don't only harm children's developing lungs – they can actually cross the blood-brain barrier and permanently damage their developing brains – and, thus, their futures," Lake added. "No society can afford to ignore air pollution."
Outdoor air pollution can be caused by a range of factors, from the burning of waste to vehicle emissions and the use of fossil fuels, UNICEF said.
The report also looked at indoor pollution, often caused by using "dirty" fuels to cook food and heat homes. UNICEF said that outdoor and indoor pollution were linked to conditions such as pneumonia and other respiratory diseases, which accounted for nearly one in 10 deaths of children under five.
The health issues surrounding air pollution are longstanding and widely reported. The WHO says that, globally, outdoor air pollution in urban areas causes an estimated 1.3 million deaths annually, while indoor air pollution causes two million deaths.
In February this year, a report from the Royal College of Paediatrics and Child Health and the Royal College of Physicians found that outdoor air pollution was linked to roughly 40,000 deaths every year in the U.K.
The report said air pollution had been linked to wide range of diseases, from cancer to asthma, heart disease and diabetes and that damage would be inflicted "across a lifetime, from a baby's first weeks in the womb all the way through to the years of older age."
UNICEF's report comes ahead of next week's United Nations COP22 summit in Morocco, and the organization called on world leaders to take steps to protect children from air pollution. These included reducing pollution, minimizing exposure and boosting access to healthcare.
"We protect our children when we protect the quality of our air. Both are central to our future," Lake said.