Only 10 countries and territories out of 134 met World Health Organization standards for a diffuse form of air pollution last year, according to air quality data compiled by IQAir, a Swiss company.
The pollution studied is called fine particulate matter, or PM2.5, because it refers to solid particles smaller than 2.5 micrometers in size: small enough to enter the bloodstream. PM2.5 is the deadliest form of air pollution, leading to millions of premature deaths each year.
“Air pollution and climate change both have the same culprit, which is fossil fuels,” said Glory Dolphin Hammes, CEO of IQAir’s North America division.
The World Health Organization sets a guideline that people should not breathe more than 5 micrograms of fine particles per cubic meter of air, on average, over the course of a year. The US Environmental Protection Agency recently proposed tightening its standards from 12 to 9 micrograms per cubic meter.
The few oases of clean air that meet the World Health Organization’s guidelines are mainly islands, as well as Australia and the northern European countries of Finland and Estonia. Of the countries that failed, where the vast majority of the human population lives, the countries with the worst air quality were mainly in Asia and Africa.
Where some of the dirtiest air is
The four most polluted countries in IQAir’s 2023 ranking — Bangladesh, Pakistan, India and Tajikistan — are located in South and Central Asia.
Air quality sensors in nearly a third of the region’s cities reported concentrations of fine particles that were more than 10 times WHO guidelines. That was a ratio “far exceeding that of any other region,” the report’s authors wrote.
The researchers pointed to vehicular traffic, coal and industrial emissions, particularly from brick kilns, as the main sources of pollution in the area. Farmers who seasonally burn their crop waste contribute to the problem, as do households who burn wood and dung for heat and cooking.
China reversed recent gains
A notable change in 2023 was China’s air pollution increasing by 6.3% compared to 2022, after at least five years of improvement. Beijing saw a 14 percent increase in PM2.5 pollution last year.
The national government announced a “war on pollution” in 2014 and has made progress since then. However, the sharpest decline in PM2.5 pollution in China occurred in 2020, when the coronavirus pandemic forced much of the country’s economic activity to slow or shut down. Ms Dolphin Hammes attributed last year’s rise to a reopening economy.
And challenges remain: Eleven cities in China reported air pollution levels last year that exceeded WHO guidelines by 10 times or more. The worst was Hotan, in Xinjiang.
Significant data gaps
IQAir researchers analyze data from more than 30,000 air quality monitoring stations and sensors in 134 countries, territories and disputed territories. Some of these monitoring stations are run by government agencies, while others are overseen by non-profit organizations, schools, private companies and citizen scientists.
There are major gaps in ground-level air quality monitoring in Africa and the Middle East, including areas where satellite data show some of the highest levels of air pollution on Earth.
As IQAir works to add data from more cities and countries in the coming years, “the worst may be yet to come in terms of what we’re measuring,” Ms Dolphin Hammes said.
Fire smoke: a growing problem
Although North America is one of the cleanest regions in the world, in 2023 wildfires burned 4 percent of Canada’s forests, an area roughly half the size of Germany, and significantly reduced air quality.
Usually, the list of the most polluted cities in North America is dominated by the United States. But last year, the top 13 spots all went to Canadian cities, many of them in Alberta.
In the United States, cities in the Upper Midwest and Mid-Atlantic states also received significant amounts of PM2.5 pollution from wildfire smoke that drifted across the border.
Risks of short-term exposure
It’s not just chronic exposure to air pollution that harms people’s health.
For vulnerable people, such as the very young and elderly, or those with underlying illnesses, breathing large amounts of particulate pollution for just a few hours or days can sometimes be fatal. About 1 million premature deaths per year can be attributed to short-term exposure to PM2.5, according to a recent global study published in The Lancet Planetary Health.
The problem is worse in East and South Asia, as well as West Africa.
By not accounting for short-term exposures, “we may be underestimating the mortality burden of air pollution,” said Yuming Guo, a professor at Monash University in Melbourne, Australia, and one of the study’s authors.
Inequality is widening in the US
In individual countries, air pollution and its effects on health are not evenly distributed.
Air quality in the United States has generally improved since the Clean Air Act of the 1970s. Over the past decade, premature deaths from exposure to PM2.5 have fallen to about 49,400 in 2019, from about 69,000 in 2010.
But progress has been faster in some communities than in others. Racial and ethnic disparities in air pollution deaths have grown in recent years, according to a national study released this month.
Counties in the United States with the fewest white residents have about 32 percent higher PM2.5-related death rates, compared to those with the most white residents. This difference in deaths per capita increased by 16% between 2010 and 2019.
The study looked at race and ethnicity separately and found that the gap between census tracts with the most and least Hispanic residents grew even more, by 40 percent.
In IQAir’s rankings, the United States does much better than most other countries. But studies that dig deeper show that air quality is still an issue, said Gaige Kerr, a researcher at George Washington University and lead author of the disparities paper published in the journal Environmental Health Perspectives. “There’s still a lot of work to be done,” he said.
The research of Dr. Kerr showed that death rates were highest on the Gulf Coast and Ohio River Valley, areas dominated by the petrochemical and manufacturing industries. He also noted that researchers have seen a slight increase in PM2.5-related death rates starting around 2016, particularly in western states, likely due to increasing wildfires.
