I don’t think anyone thinks the majority of the air in major metropolitan areas around the world is particularly clean. That said, it is a bit surprising, at least to me, to find out that air quality the world over should be making us cringe.

The harmful pollutants are known as PM 2.5, and according to this huge recent study, only 0.001 percent of the global population live in areas where the levels are consistently below thresholds the World Health Organization (WHO) deems safe.

Yuming Guo, the study’s lead author, describes what surprised them about the study.

“Almost no one is safe from air pollution. The surprising result is that almost all parts of the world have annual average PM 2.5 concentrations higher than air quality guidelines recommended by the World Health Organization.”

What is PM 2.5? It’s a fine air particulate that’s no more than 2.5 microns in width, which is 30 times smaller than a grain of sand. It’s small size makes it able to easily access our lungs and bloodstream. Experts say we should worry about both lung cancer and heart disease.

Research done by the Environmental Protection Agency (EPA) suggests that exposure for as little as a few hours can trigger “cardiovascular disease-related heart attacks and death.”

Long-term exposure can lead to an “increased risk of cardiovascular mortality and decreases in life expectancy.”

And get this – the threshold used to be higher; the WHO revised its air quality guidelines recently to reduce it from 10 micrograms per cubic meter to just five.

Guo’s team was able to provide insights on the daily levels of this particulate across the world by combining ground data, satellite-based meteorological data, and an “innovative machine learning approach to integrate” all of the above.

The daily levels of PM 2.5 have dropped in North America and Europe over the past 20 years but continue to climb in regions like Southern Asia, Latin America, and Australia.

Average levels are around 32.8 micrograms per cubic meter, which is 6 times the threshold recommended by the WHO.

It’s not surprising, then, to find the results of other studies blaming air pollution for around 9 million premature deaths every year.

Guo hopes the results of his study could help things start to change.

“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.”

Scientists have been ringing these kinds of bells for decades now, and it seems like things are only getting worse.

Here’s hoping there’s still time to turn the train around.