The World Health Organisation (WHO) has strengthened its air quality guidelines, saying air pollution was now one of the biggest environmental threats to human health, causing seven million premature deaths a year.
It said urgent action was needed to reduce exposure to air pollution, ranking its burden of disease on a par with smoking and unhealthy eating.
"WHO has adjusted almost all the air quality guideline levels downwards, warning that exceeding the new... levels is associated with significant risks to health," it said on Wednesday.
"Adhering to them could save millions of lives."
"There is nothing more essential for life than air quality," WHO Director-General Tedros Adhanom Ghebreyesus told reporters.
"And yet, because of air pollution, the simple act of breathing contributes to 7 million deaths a year. Almost everyone around the world is exposed to unhealthy levels of air pollution."
The guidelines aim to protect people from the adverse effects of air pollution and are used by governments as a reference for legally-binding standards.
The UN health agency last issued air quality guidelines, or AQGs, in 2005, which had a significant impact on pollution abatement policies worldwide.
However, the WHO said in the 16 years since, a much stronger body of evidence had emerged, showing how air pollution impacts on health at lower concentrations than previously understood.
Air pollution is now comparable to other global health risks like unhealthy diets and smoking tobacco, WHO said. It is recognised "as the single biggest environmental threat to human health," Dr. Dorota Jarosinska, WHO Europe programme manager for living and working environments, said.
Southeast Asia hard-hit
The new guidelines come just in time for the COP26 global climate summit held in Glasgow from October 31 to November 12.
The WHO said that alongside climate change, air pollution was one of the biggest environmental threats to human health.
Improving air quality would enhance climate crisis mitigation efforts, and vice versa, it said.
The WHO's new guidelines recommend air quality levels for six pollutants, including ozone, nitrogen dioxide, sulphur dioxide, and carbon monoxide.
The other two are PM10 and PM2.5 - particulate matter equal or smaller than 10 and 2.5 microns in diameter.
Both are capable of penetrating deep into the lungs.
In 2019, more than 90 percent of the world's population lived in areas where concentrations exceeded the 2005 AQG for long-term PM2.5 exposure.
Southeast Asia is the worst-affected region.
Difficulty in pursuing WHO guidelines
"We hope the tighter standards will draw attention to just how critical clean air is for human and ecosystem health," Jessica Seddon, global lead for air quality at the World Resources Institute, said.
"The difficulty will come in making the WHO guidelines meaningful for the average person going about their day."
"What matters most is whether governments implement impactful policies to reduce pollutant emissions, such as ending investments in coal, oil, and gas and prioritising the transition to clean energy,” said Dr. Aidan Farrow, a Greenpeace international air pollution scientist who is based at Britain's University of Exeter.
"The failure to meet the outgoing WHO guidelines must not be repeated," he said in a statement.