The cities with the most and fewest good air days

By
Updated on April 15, 2024
Written by
Danny Ashton
Danny is the founder of HouseFresh and has been writing about air purifiers and indoor air quality since 2010. He is our lead tester, conducting all the tests we use to evaluate air quality products. That is why you will always see his name attached to our reviews.

Few things affect a person’s quality of life more than good air. Data from the Institute for Health Metrics and Evaluation shows ambient particulate matter as the sixth leading cause of global excess deaths each year. The World Health Organization (WHO) claims that 93% of the world’s children breathe air with higher levels of pollution, and medical studies have demonstrated the connection to respiratory diseases, including lung cancer.

While rising global temperatures and the climate crisis are existential threats to humanity, air pollution from fossil fuels is an immediate risk to human life, with a study from Harvard University linking fine particulate matter (PM 2.5) to one in five excess deaths globally. These air particles, which occur naturally and through man-made activity, are roughly 2.5 micrometers in diameter — around 30 times smaller than a strand of human hair.

Removing pollution from the atmosphere and exposing the world’s population to clean air is a major priority, with the United Nations listing it as one of their Sustainable Development Goals. The benefits of clean air are plain to see: reduced illnesses and death, improved quality of life and healthier and more sustainable cities.

The U.S. Air Quality Index (AQI) is a widely-accepted barometer for air quality and ranks pollution levels based on the concentration of PM 2.5 particles in the atmosphere. These range from “Good,” with less than 12 µg/m3, to “Hazardous,” with more than 35 μg/m3.

To find out which cities around the world have the cleanest air, HouseFresh analyzed pollution levels in more than 500 global urban areas, ranking them to see which locations have the most and fewest good air days.

How we conducted this study

Particulate matter (PM 2.5) pollution data was sourced from the World Air Quality Index database of air quality measures, with supplementary data from the AirNet API. Pollution values represent PM 2.5 pollution levels in each city, expressed as micrograms per cubic meter of air, or µg/m3, an average of daily observations during a given year.

The number of “Good Air Days,” as defined under the U.S. Air Quality Index (AQI), was taken as the total number of days where the PM 2.5 concentration was below 12 µg/m3.

We have reviewed the data and, according to the World Air Quality Index, all air quality monitoring stations in Calama report good air quality, with three stations reporting that there has been good air quality for the last 12 months. We have double-checked this data against IQAir’s air quality data for Chile, and it also shows Calama as one of the cities with the cleanest air in the country regarding PM2.5 air pollution.

Even though this data is correct from a methodological point of view, it might not be reflective of other types of air quality issues experienced by residents of Calama. In fact, there is currently a decontamination plan being discussed by the local government to tackle PM10 pollution by regulating mining activities and their associated emissions in the area. 


Key findings

  • Nine cities, including six in Australia and New Zealand, have 365 days of good air every year.
  • Zürich, Switzerland, and Reykjavik, Iceland, have the most ‘good air days’ in Europe, with 365 days of low pollution.
  • Los Angeles, Fresno and San Diego — all in California, have the lowest amount of good air days in the U.S., with less than 250 days with low pollution during the year.
  • Honolulu, Hawaii, has America’s lowest pollution for a major city, with 365 days where the PM 2.5 concentration is below 12 µg/m3.

Looking for clean air? Move to Australia

Improving air quality in major cities is an expensive challenge for metropolitan mayors around the world. WHO data shows that 9 in 10 people living in cities breathe polluted air. From transportation schemes to reduce car and bus emissions to renewable energy programs to decarbonize a city’s power grid, the world’s major cities are taking serious steps to reduce air pollution and improve the quality of life for their residents.

But if you’re looking to move to a city with clean air, our research shows that the best place to start is Australia. Six of the ten global urban areas with the most good air days can be found there, all of which benefit from 365 days a year without high levels of PM 2.5 matter in the atmosphere.

Sydney, Australia’s largest urban area, is one of these locations. It is frequently recognized as one of the world’s most livable cities and is home to more than 400 parks and green spaces. However, the city is growing rapidly. Research from the University of Wollongong has created a blueprint for Sydney to lower its air pollution moving forward, from banning diesel vehicles to reducing smoke pollution from wood heaters.

Only one city in the Americas enjoys 365 days of good air per year — Honolulu, Hawaii. Located around 2,000 miles from the U.S. mainland, its residents benefit from some of the cleanest city air in the world. This is likely a result of Hawaii’s strict anti-pollution regulations, and the state is recognized by the American Lung Association for its low PM 2.5 levels.

At the opposite end of the spectrum, four of India’s major cities have one day or less each year of good air. This could be a result of the country’s geography, where pollution in the country’s northern states is trapped by the Himalayan mountains — an occurrence felt especially in the winter months. As an emerging economy reliant on heavy industry and fossil fuel usage, 93% of its population is exposed to unsafe levels of PM 2.5 matter.

Los Angeles has fewer than five months of clean air each year

The White House Office of Science and Technology Policy lists a range of benefits from cleaner air, from the improvement of cognition and productivity to the reduction of environmental triggers for conditions like asthma and allergies. However, a report from the American Lung Association shows that 63 million Americans in 96 counties are subject to the country’s poorest levels of air quality.

Our research shows that six major urban areas in California have the lowest total number of good air days in the country, and its largest city Los Angeles has 71 fewer days with low pollution than anywhere else. With a sprawling urban population of 18 million people, the City of Angels is notorious for its smog and pollution.

It has some of the worst traffic corridors in the U.S., and reports from the Environmental Protection Agency suggest that pollution levels have been at their highest in the area since 2010. While other major urban areas in the state, including Fresno (240 good air days), San Diego (246 days) and Sacramento (294 days), are short of good air days, California’s state government has taken action to improve the state’s air quality record.

In November 2022, Governor Gavin Newsom unveiled a plan to reduce air pollution by 71% and greenhouse gas emissions by 85%. At the same time, the state is facing a battle to secure funding for a proposed high-speed rail line to connect Los Angeles and San Francisco — a plan that would cut carbon emissions by 100 million metric tons within 50 years.

America’s largest metropolitan area New York is a stark contrast to its West Coast counterpart. Despite being home to two million more residents than Los Angeles, it sees good air days for 340 days of the year, making it one of the country’s cleanest cities. New York City has cut its PM 2.5 pollution levels by 40% over the last 20 years, transforming itself away from toxic air quality that plagued the health of its residents for decades.

Nordic cities among Europe’s cleanest air locations

Air quality in Europe is subject to tougher regulation than other parts of the world. For the 27 countries in the European Union, a directive restricts the quantity of fine particulate matter in the atmosphere. Brussels took this a step further in November 2022, limiting PM 2.5 matter to 10 µg/m3 in response to data from the European Environment Agency, which links 307,000 excess deaths in the continent to air pollution.

Our research shows that two major European cities (both outside of the EU) have 365 days a year of good air — Zurich, Switzerland, and Reykjavik, Iceland. Located 600 miles off the coast of continental Europe, Iceland’s small population (approx. 300,000) and clean energy production contribute to its low particulate matter levels. Reykjavik is one of six Nordic cities with the most good air days, according to our research. Sweden, Finland, Denmark, Norway and Iceland cooperate directly on air quality through the Nordic Council.

However, three major cities in southeastern Europe have less than 100 good air days each year. The capitals of Pristina (27 days), Nicosia (75 days) and Sarajevo (97 days) are among Europe’s most polluted, according to our research. Kosovo’s energy sector is predominantly reliant on coal, with two major plants polluting Pristina’s air to such an extent that residents have protested against the state’s policy.

Lowering air pollution in the world’s major cities

Air pollution in major cities is a huge stumbling block for the world’s climate scientists. United Nations data predicts that 68% of the global population will live in urban areas by 2050. Yet air quality data shows that residents in many of the world’s largest cities struggle to enjoy good air days, potentially causing long-term damage to their respiratory health and well-being.

You can explore our full dataset of 500+ urban areas below, allowing you to see which cities have the most and fewest good air days where you live.

As our cities continue to grow and population centers become more concentrated, how can societies ensure sustainable living conditions for decades to come? Getting it right is central to the commitment made by national governments to the UN’s Sustainable Development Goals. A 2021 report on this issue found that most cities are shifting their focus toward the decarbonization of heavy industry and low-carbon transportation (e.g., vehicle emissions standards).

However, the clock is ticking on air quality as the urgency of the climate crisis mounts. With WHO data indicating that 80% of city dwellers are still exposed to excessive fine particulate matter levels, major metropolitan areas must continue to prioritize the health of their residents by directly targeting air pollution.

The method behind the study

To find the global and American Cities with the most and fewest good air days, we sourced particulate matter (PM 2.5) pollution from the World Air Quality Index database of air quality measures, with supplementary data from the AirNet API. Only cities that have data from at least two (2) monitoring stations for at least 300 days of the year 2022 were included in the dataset. 

Pollution values represent PM 2.5 pollution levels in each city, expressed as micrograms per cubic meter of air, or µg/m3, an average of daily observations during a given year.

To arrive at these numbers, AQI PM2.5 was converted into µg/m3 values using a formula developed by AirNow, a partnership of the U.S. Environmental Protection Agency, National Oceanic and Atmospheric Administration (NOAA), National Park Service, NASA, Centers for Disease Control and tribal, state and local air quality agencies.

The number of “Good Air Days” was taken as the total number of days where the PM 2.5 concentration was below 12 µg/m3. This is defined under the U.S. Air Quality Index (AQI).

Cities in Ukraine were excluded from the comparison due to the ongoing military conflict having an inevitable impact on the level of air pollution.

New York City pollution levels were calculated by aggregating the data from Manhattan, The Bronx, Staten Island, Brooklyn and Queens by taking the median pm2.5 values on each day.

At HouseFresh, we have been reviewing air quality products since 2010, and this includes air quality monitors like the Purpleair Indoor Sensor II, which also provides shared air quality data with the world that helps support big data campaigns like this. If you have any questions about our testing process for different air-quality products, just email us at hello@housefresh.com.

Join our newsletter

We’ll send you a nice email every once in a while. No spam.

Support HouseFresh

Buy us a coffee
Your support makes it possible for us to keep doing what de wo.
About the author

Danny Ashton

Danny is the founder of HouseFresh and has been writing about air purifiers and indoor air quality since 2010. He is our lead tester, conducting all the tests we use to evaluate air quality products. That is why you will always see his name attached to our reviews.

Join our newsletter

We’ll send you a nice email every once in a while. No spam.

Support HouseFresh

Buy us a coffee
Your support makes it possible for us to keep doing what we do.
We are ad-free and buy all the devices we test with our own money. When you buy through links on our site, we may earn an affiliate commission, which we use to fund new product tests. Learn more