Air pollution from wildfire smoke and many other sources, the focus of Wednesday’s World Environment Day, is unfortunately a growing problem around the world.

The World Health Organization recently reported that nine out of 10 people breathe polluted air, and that 7 million people die each year due to these hazards.

At the country level, India has some of the worst air anywhere — when you look at ranking of particulate pollution in cities, 11 of the 12 cities with the highest levels are in India.

The ozone, sulfur and nitrogen compounds, and fine particles that comprise this pollution can inflame airways, which in turn can trigger breathing issues and heart problems, and exacerbate illnesses. During previous wildfires in California, researchers found that emergency room visits for asthma, heart attacks, and strokes spiked in areas under dense smoke.

And all these health effects can add up to years of life lost. A 2015 study found that India’s air pollution trimmed 3.2 years from the life expectancy of 660 million people living in the country.

The Energy Policy Institute at the University of Chicago in 2018 launched an interactive tool that shows just how much different parts of the world would benefit if they breathed clean air. The Air Quality Life Index maps fine particulate air pollution concentrations and calculates how many years of life people living in an area would potentially gain if their air quality improved to meet WHO guidelines. The WHO considers 10 micrograms of fine particulates per cubic meter on average per year as the safe limit.

Not surprisingly, places with the dirtiest air right now stand to gain the most. On average, India would rise 4.3 years in life expectancy. China would see an increase of 2.9 years.

Most of the United States averages annual particulate air pollution below the WHO’s safety threshold, so the index shows there isn’t much room for the US to improve life expectancies.

What the index does make abundantly clear is that there is a direct relationship between air pollution, namely particulate matter, and health. Dirty air costs years of life, but cleaning it up yields huge dividends for billions of people. If current levels of particulate air pollution persist, the global population would lose 12.8 billion years of life. This would cost the average person 1.8 years of life.

By comparison, smoking shaves 1.6 years off of global average life expectancy. Poor sanitation cuts life expectancies by seven months. Conflict and terrorism costs 22 days.

Some of the particulates come from sources like wildfires, making them difficult to clean up. But other sources, like vehicles, power plants, and agriculture, can cut particulates by electrifying, using scrubbers, or employing dust mitigation tactics.

One limitation of the tool is that the pollution measurements in the index are based on annual averages. This highlights the most consistently polluted regions but obscures seasonal or short-term pollution spikes, like those surrounding California’s wildfires. These peaks can cause increases in emergency room visits in as little as 24 hours, so they’re still important to public health.

And fine particulates, classified as 2.5 microns or less in diameter, are just one type of pollution. Different parts of the world experience a different mix of hazards, so low particulate pollution in one area could still mean higher levels of ozone, volatile organic compounds, or nitrogen oxides.

So when someone brags about clean air in the United States using annual particulate measurements, know that it doesn’t tell the whole story.