The World Health Organisation (WHO) has slashed recommended limits for key air pollutants in the face of growing evidence of their damage to health.

In the first global update of its air quality guidelines since 2005, the health body has significantly tightened recommended average annual limits for dangerous tiny particles known as PM2.5 and for nitrogen dioxide pollution.

The WHO said clean air should be a “fundamental human right” but millions were dying early each year or suffering ill health due to toxic air pollution, making it a global health risk on a par with smoking and unhealthy diets.

There has been a marked increase in the evidence of the adverse impacts of air pollution on human health in the past 15 years since the last guidelines.

The new guidelines reflect evidence of the harm these air pollutants can do, at even lower concentrations than previously understood, reducing the limits to protect people’s health, the WHO said.

Environmental campaigners in the UK said the changes meant that British legal limits for PM2.5 and nitrogen dioxide were now four times higher than the WHO recommendations.

Environmental law charity ClientEarth, which has won a series of cases against the Government over air pollution, said citizens were being exposed to toxic pollution far above what was known to be acceptable and ministers should be “scrambling to act” to tighten UK targets.

Outdoor air pollution comes mostly from burning fuels in vehicles, power plants, and heating and cooking in homes through the use of boilers or wood stoves, as well as industry, waste incineration and agriculture.

Pollutants can cause reduced lung growth and function in children, as well as respiratory infections and aggravated asthma, while heart disease and stroke are the most common causes of premature death due to air pollution in adults.

Evidence is also emerging of other effects such as diabetes and other conditions such as dementia, the WHO said.

The health risks of particulate matter are of particular concern, with PM2.5 able not only to penetrate deep into the lungs but also enter the bloodstream, with impacts on the heart and blood system and other organs.

In 2019, more than 90% of people in the world were living in areas where concentrations exceeded the 2005 air quality guidelines for long-term exposure to PM2.5, the WHO said.

The health body said air pollution was one of the biggest health risks alongside climate change, but improving air quality can also help with cutting climate emissions.

WHO regional director for Europe, Dr Hans Henri Kluge, said: “Annually, WHO estimates that millions of deaths are caused by the effects of air pollution, mainly from non-communicable diseases.

“Clean air should be a fundamental human right and a necessary condition for healthy and productive societies.

“However, despite some improvements in air quality over the past three decades, millions of people continue to die prematurely, often affecting the most vulnerable and marginalised populations.”

“These updated guidelines give policy-makers solid evidence and the necessary tool to tackle this long-term health burden.”

The WHO’s new guidelines recommend air quality limits for six pollutants – types of particulate matter PM10 and PM2.5, ozone, nitrogen dioxide, sulphur dioxide and carbon monoxide – and most of the targets have been tightened.

The annual average recommended limit for PM2.5 has been halved, and the annual limit for nitrogen dioxide has been reduced by three quarters, with interim targets to help meet the guidelines.

Andrea Lee, clean air campaigns manager at ClientEarth, said: “These new guidelines reflect the best available science and the conclusion is irrefutable: air pollution, even at levels lower than previously thought, seriously endangers people’s health and action needs to be taken.

“This must serve as a wake-up call for the UK Government – ministers should be scrambling to act.

“As the Environmental Bill is currently going through Parliament, the Government needs to listen to the health evidence, show leadership and get on with tightening air quality standards that better protect people now.”

Rosamund Adoo-Kissi-Debrah, whose daughter Ella died of an asthma attack after being exposed to toxic air pollution said: “Air pollution stunts children’s health and future – it causes premature birth, life-threatening asthma, cognitive problems, childhood cancer and so many other problems.

“There is no safe level of air pollution to breathe, but at least following the WHO’s new air quality guidelines will improve children’s health and set us on the path to achieving clean air for all.”

She urged the Government to include air quality targets in the current Environment Bill that follow the WHO’s guidelines, rather than wait for a consultation.

“It’s incredibly disappointing to see Prime Minister Boris Johnson telling other countries at the UN this week that they are not doing enough to tackle climate change, when his own government is still supporting new fossil fuel projects and delaying air quality targets that will save lives now and help reach net zero emissions by 2050.”

Acting shadow environment secretary Daniel Zeichner said: “Inaction and delay from the Conservatives has allowed catastrophic levels of air pollution to build up across the country, with toxic air estimated to cause around 40,000 premature deaths a year.

“In Government, Labour would introduce a new Clean Air Act to protect our environment, help decarbonise the economy and ensure we all have safe air to breathe.”

An Environment Department (Defra) spokesperson said the Government would set stretching and ambitious targets on air quality, and would be running a consultation on the proposed targets early next year.

“We will consider the updated WHO guidelines on PM2.5 to inform the development of air quality targets but we must not underestimate the challenges these would bring particularly in large cities and for people’s daily lives,” they said.

Sarah Woolnough, chief executive of Asthma UK and the British Lung Foundation, said the Government had dragged its heels long enough on air pollution.

“With this latest WHO guidance, COP26 on the horizon and the Environment Bill going through parliament, now is the time for politicians to commit to world-leading air pollution targets to tackle the greatest environmental threat to human health.

“We have a front row seat to the devastation caused by breathing in dirty air which creates new lung conditions, worsens existing ones and triggers life-threatening asthma attacks, and it’s plain to see that the government’s current air quality legal limits are unfit for purpose.”