Warning over air quality improvement slowdown

China’s air quality improvement has slowed dramatically over the past five years.

A new study, which analysed 10 years of data, found that since 2020 the country’s period of rapid reduction in fine particulate matter (PM2.5) had ended while ozone (O3) levels had continued to increase, despite other studies predicting they would fall.

It suggests that without urgent and ambitious government action, deaths in China caused by PM2.5 – tiny particles that penetrate the lungs – look set to increase.

Scientists behind the research say the country must now hit its air quality goals around twice as fast to avert a rise in avoidable deaths.

Ageing population more vulnerable to PM2.5

The team explains that China's rapidly ageing population is a major contributor to the problem as the older someone is, the more vulnerable they are to PM2.5 air pollution.

They warn it is a race against time to improve the country’s air quality fast enough to counter the effect of population ageing on mortality rates.

More than two million people in China are estimated to die early each year due to PM2.5 air pollution exposure.

This number had been falling due to a rapid improvement in air quality in the 2010s when the country made huge changes in its “war on pollution,” but this study has found it now looks likely to start rising again.

The paper, “A decade of China’s air quality monitoring data suggests health impacts are no longer declining” is published in Environment International.

The team hope that by sharing their findings they will provide evidence to support further action and improve the lives and health of millions.

The paper’s lead author Postdoctoral Research Fellow Dr Ben Silver, from the School of Earth and Environment, said: “The current narrative is that China has rapidly improved air quality and ‘won the war’ on air pollution.

“While it is true that the improvement in air quality during the 2010s was an outstanding achievement, it should be recognised that continuing to improve air quality is not so easy.

“This slowdown over the past five years, coupled with the country’s ageing population, means there’s still a serious air pollution problem.”

Action on air pollution

China is not only the country with the second largest population on Earth, but it is also one of the countries with the fastest ageing population.

This is mainly due to decades of falling birth rates on the one hand and steeply rising life expectancy on the other.

In 2013, when China’s pollution hit record levels, the government prohibited new coal-fired power plants, shut down coal mines and restricted the number of cars on the road.

Its Air Pollution Action Plan helped the nation make significant improvements between 2013 and 2017, reducing PM2.5 levels by 33% in Beijing and 15% in the Pearl River Delta region.

PM2.5 refers to particulate matter where the particles are smaller than 2.5 micrometres in diameter.

Their tiny size means they can penetrate deep into the respiratory system and even enter the bloodstream, causing a range of adverse health effects

World Health Organisation (WHO) air quality guidelines (AQG) offer global guidance on key air pollutants that pose health risks.

It currently recommends PM2.5 annual mean concentrations be kept below 5 microgram per cubic metre (μg/m3).

China has adopted a target of 25 PM2.5 μg/m3 by 2030, equivalent to the second WHO interim target for PM2.5.

Interim targets are air pollutant levels that are higher than the AQG levels, but which authorities in highly polluted areas can use to develop pollution reduction policies that are achievable within realistic time frames.

However, partly due to the slowdown in air quality improvement and partly due to China’s ageing population, even if China meets its current target the number of annual fatalities resulting from PM2.5 will still increase, according to this study.

It suggests the government’s target needs to be around twice as ambitious to reduce deaths.

Major challenges in preventing harmful impacts

Stephen Arnold, Professor of Atmospheric Composition in the School of Earth and Environment, who supervised the research, said: “These findings emphasise the importance of monitoring data for detecting changes in the exposure of people to harmful air pollution.

“The recent improvements that China has achieved in air pollution are slowing, and this will present major challenges in preventing harmful health impacts, particularly as the population grows and becomes older.

“Our research provides new information on how pollution levels will need to be reduced further to meet this challenge.”

The Leeds team used a new “robust trend-fitting technique” to analyse historical air quality data, then generated three hypothetical future PM2.5 scenarios to demonstrate the health impact of potential future trajectories of China’s PM2.5 concentrations.

Dr Silver said the China National Environmental Monitoring Centre (CNEMC) had created an “impressive” network of around 2,000 air quality stations, which have provided more than 800 million hourly measurements since 2014.

He said: “Despite the data being collected, it is not easily accessible. But it is a much-needed resource as China’s air pollution doesn't just affect China, it affects the global climate.”

Dr Silver said future trends should continue to be closely monitored to understand whether the apparent slowdown in improvement was temporary or the new standard. Further research could explore the emissions reduction policies required to achieve the PM2.5 decrease this study suggests is necessary, to resume reduction of negative health impacts.

The research was funded by AIA Group Limited, and the UK Research and Innovation (UKRI) Natural Environment Research Council (NERC).