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Mapped: Which Countries Have the Worst Air Pollution?

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Mapped: Which Countries Have the Worst Air Pollution?

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In many parts of the world, blue skies are a rarity. Instead, accumulated levels of air pollution from industrial processes and motor vehicle traffic cloak cities in smog year-round.

But to what extent does air pollution impact the human population around the world?

To answer this question, data scientist Matt Dzugan has created a cartogram that shades each country based on levels of fine particulate matter (PM2.5) air pollution experienced by the population living there.

Carto-What?

First off, let’s talk about the visualization style itself.

Not your everyday map, this unconventional cartogram resizes the borders of countries based on their total populations. In this style, a single square represents 500,000 people. According to Matt Dzugan, the cartogram view is meant to provide a bird’s eye perspective of the impact of air pollution and fine particulate matter (PM2.5) on human lives.

A clear correlation emerges: some of the most inhabited places in the world also experience the most pollution. Highly populated China and India show up the most prominently, while other countries like Australia and Canada seem to disappear off the map entirely.

To put this into perspective, 800 dark brown squares on this cartogram (a PM2.5 concentration of 50 μg/m³) represent 400 million people in India that are exposed to polluted air at levels five times past thresholds set by the World Health Organization.

Top 20 Countries with Cleanest Air

So how do countries on each end of the PM2.5 spectrum shake out? Pulling supplemental data from the WHO, here’s how the top 20 countries with the cleanest air rank.

Countries with the Cleanest Air Supplemental

New Zealand tops the above list. And as you can see, air quality tends to be highest in advanced coastal economies with low population densities—and being an island or bordering less habitable Arctic tundra also helps as well.

That said, there are temporary bouts when air quality can dip in even the best of countries. For example, recent wildfires on the West Coast of the United States and Australia resulted in reddish-orange skies and hazardous levels of air quality for weeks at a time.

The 20 Countries with the Most Air Pollution

On the other hand, it may be surprising that Nepal lands all the way at the bottom of the air quality list. Why is this landlocked country—home to less than 30 million—suffering from hazardous air pollution reaching 100μg/m³?

In short, the emissions from fossil-fuel driven traffic and manufacturing operations are trapped within the Kathmandu valley, which causes air quality issues for people living in the region.

Countries with the Most Air Pollution

The regions with lower air quality tend to be more landlocked with developing economies, such as some countries in central Africa and Asia, as well as in the Middle East.

Finally, while China is lower on this overall list, it’s worth noting that it is one of the most prominent on the cartogram due to its sheer population size.

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The Most Polluted Cities in the U.S.

What are the most polluted cities in the U.S. according to data from the American Lung Association’s 2024 State of the Air Report?

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Teaser image for an infographic showing the most polluted cities in the U.S. according to the American Lung Association's 2024 State of the Air report.

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The following content is sponsored by National Public Utilities Council

The Most Polluted U.S. Cities in 2024

According to the World Health Organization, air pollution is responsible for 7 million deaths annually, and could cost the global economy between $18–25 trillion by 2060 in annual welfare costs, or roughly 4–6% of world GDP.

And with predictions that 7 in 10 people will make their homes in urban centers by mid-century, cities are fast becoming one of the frontlines in the global effort to clear the air.

In this visualization, we use 2024 data from the State of the Air report from the American Lung Association to show the most polluted cities in the United States.

What is Air Pollution?

Air pollution is a complex mixture of gases, particles, and liquid droplets and can have a variety of sources, including wildfires and cookstoves in rural areas, and road dust and diesel exhaust in cities. 

There are a few kinds of air pollution that are especially bad for human health, including ozone and carbon monoxide, but here we’re concerned with fine particulate matter that is smaller than 2.5 microns, or PM2.5 for short. 

The reason for the focus is because at that small size, particulate matter can penetrate the bloodstream and cause all manner of havoc, including cardiovascular disease, lung cancer, and chronic pulmonary disease. 

The American Lung Association has set an annual average guideline of 9 µg/m³ for PM2.5, however, the World Health Organization has set a much more stringent limit of 5 µg/m³.

The 21 Worst Polluted Cities in the U.S.

Here are the top 21 most polluted cities in the U.S., according to their annual average PM2.5 concentrations:

RankCity, StateAnnual average concentration, 2020-2022 (µg/m3)
1Bakersfield, CA18.8
2Visalia, CA18.4
3Fresno, CA17.5
4Eugene, OR14.7
5Bay Area, CA14.3
6Los Angeles, CA14.0
7Sacramento, CA13.8
8Medford, OR13.5
9Phoenix, AZ12.4
10Fairbanks, AK12.2
11Indianapolis, IN11.9
12Yakima, WA11.8
13Detroit, MI11.7
T14Chico, CA11.6
T14Spokane, WA11.6
15Houston, TX11.4
16El Centro, CA11.1
17Reno, NV11.0
18Pittsburgh, PA10.9
T19Kansas City, KS10.8
T19Las Vegas, NV10.8

Note: The American Lung Association uses Core Based Statistical Areas in its city and county rankings, which have been shortened here to the area’s principal city, or metro area in the case of the Bay Area, CA.

Six of the top seven cities are in California, and four in the state’s Central Valley, a 450-mile flat valley that runs parallel to the Pacific coast, and bordered by the Coast and Sierra Nevada mountain ranges. As a result, when pollution from the big population centers on the coast is carried inland by the wind—cities #5 and #6 on the list—it tends to get trapped in the valley. 

Bakersfield (#1), Visalia (#2), and Fresno (#3) are located at the drier and hotter southern end of the valley, which is worse for air quality. The top three local sources of PM2.5 emissions in 2023 were farms (20%), forest management / agricultural waste burning (20%), and road dust (14%). 

Benefit to Economy

While the health impacts are generally well understood, less well known are the economic impacts.

Low air quality negatively affects worker productivity, increases absenteeism, and adds both direct and indirect health care costs. But the flip side of that equation is that improving air quality has measurable impacts to the wider economy. The EPA published a study that calculated the economic benefits of each metric ton of particulate matter that didn’t end up in the atmosphere, broken down by sector. 

SectorBenefits per metric ton
Residential Woodstoves$429,220
Refineries$333,938
Industrial Boilers$174,229
Oil and Natural Gas Transmission$125,227
Electricity Generating Units$124,319
Oil and Natural Gas$88,838

At the same time, the EPA recently updated a cost-benefit analysis of the Clean Air Act, the main piece of federal legislation governing air quality, and found that between 1990 and 2020 it cost the economy roughly $65 billion, but also provided $2 trillion in benefits

Benefit to Business

But that’s at the macroeconomic level, so what about for individual businesses?

For one, employees like to breathe clean air and will choose to work somewhere else, given a choice. A 2022 Deloitte case study revealed that nearly 70% of highly-skilled workers said air quality was a significant factor in choosing which city to live and work in.

At the same time, air quality can impact employer-sponsored health care premiums, by reducing the overall health of the risk pool. And since insurance premiums averaged $7,590 per year in 2022 for a single employee, and rose to $21,931 for a family, that can add up fast. 

Consumers are also putting their purchase decisions through a green lens, while ESG, triple-bottom-line, and impact investing are putting the environment front and center for many investors.

And if the carrot isn’t enough for some businesses, there is the stick. The EPA recently gave vehicle engine manufacturer Cummins nearly two billion reasons to help improve air quality, in a settlement the agency is calling “the largest civil penalty in the history of the Clean Air Act and the second largest environmental penalty ever.”

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