99% of People Breathe Dangerous Particulate Matter, Study Finds

Only 0.001 percent of the world’s population breathed in air considered safe by the World Health Organization (WHO) in 2019.

That’s the conclusion of a first-of-its-kind study published in The Lancet Planetary Health Monday that used a combination of air quality data and machine learning techniques to assess global concentrations of particulate matter (PM)2.5 between 2000 and 2019. 

“Almost no one is safe from air pollution,” lead study author and Monash University professor Yuming Guo told The Washington Post in an email. 

PM2.5 exposure is a major public health threat. It is estimated that outdoor air pollution – including PM2.5 – was responsible for nearly seven million early deaths in 2019. It is so dangerous because its small size means it can enter the blood through the lungs, leading to heart disease, respiratory disease and cancers, according to the WHO. There is also increasing evidence that it can impact cognitive ability and mental health.

“No safe threshold for PM2·5 has been identified below which no damage to health is observed,” the study authors wrote. 

Because of these risks, the WHO raised its PM2.5 safety limits in 2021 from 10 micrograms per cubic meter (μg/m3) to five μg/m3 for mean exposure over a year and from 25 μg/m3 to 15 μg/m3 for mean exposure over a single 24-hour period. 

The WHO’s air quality database – incorporating data from more than 6,000 cities and 117 countries – also found that 99 percent of people were breathing in unhealthy levels of both particulate matter and nitrogen dioxide. However, there are gaps in existing air quality monitoring stations that the new study was able to fill. 

“In this study, we used an innovative machine learning approach to integrate multiple meteorological and geological information to estimate the global surface-level daily PM2.5 concentrations at a high spatial resolution of approximately 10km ×10km for global grid cells in 2000-2019, focusing on areas above 15 μg/m3,” Guo said in a press release. 

The study authors found that the global average for yearly PM2.5 concentrations over the study period was 32.8 µg/m3. While the number of high-concentration days decreased during that time, the globe still saw concentrations higher than 15 μg/m3 more than 70 percent of the year in 2019. 

Regionally, both the annual averages and the number of high-concentration days decreased in North America and Europe and increased in Southern Asia, Australia and New Zealand and Latin America and the Caribbean. Overall, Asia had the most unhealthy air, with South and East Asia seeing concentrations above the WHO’s daily limit on more than 90 percent of days throughout the study period. North Africa also had high PM2.5 concentrations, while Australia, New Zealand, the rest of Oceania and South America had the lowest. 

On a country-by-country basis, the countries with the highest population-weighted PM2.5 exposure in 2019 were: 

1. China
2. North Korea
3. Bangladesh
4. Niger
5. South Korea
6. Mauritania
7. Armenia
8. India
9. Pakistan
10. Egypt 

The make-up of the top 10 changed throughout the study period, but China came in first for every year assessed. 

While the study is not good news for global health, Guo hopes it can be part of the solution.

“It provides a deep understanding of the current state of outdoor air pollution and its impacts on human health,” he said in the press release. “With this information, policymakers, public health officials, and researchers can better assess the short-term and long-term health effects of air pollution and develop air pollution mitigation strategies.”