The 2025 World Air Quality Report tells the story of the global fight for cleaner air – both the challenges and the successes. Though most metropolitan areas continue to grapple with air pollution, a select group of cities have shown that healthy air and city life can co-exist.
In many cases, their cleaner air is not the result of a single policy or advantage, but a combination of geography, infrastructure, monitoring, and long-term environmental planning.
These five major cities are among a small number of urban hubs that have maintained annual average PM2.5 levels at or below the World Health Organization’s (WHO) guideline of 5 µg/m3, setting a benchmark for others to follow. Their low annual averages reflect a combination of geographic advantages, long-term environmental planning, and sustained air quality management.
5. Seattle, USA
Seattle, Washington was the cleanest major U.S. city in 2025, and the only city outside of Oceania ranked among the top five in the world. With an average annual PM2.5 concentration of 4.5 µg/m3, Seattle benefits from its coastal location, which allows ocean and Puget Sound air to help disperse pollutants.
Sources of air pollution in Seattle can include maritime-related emissions, vehicle emissions, and wildfire smoke (1)(2). The city has also invested in reducing pollution from transportation and maritime activity. For instance, the Port of Seattle is collaborating with other ports on the Sound and in the Salish Sea to reduce emissions (3). Policy and regulations have also had a positive impact on port emissions.
Air quality in Seattle, Washington on May 12, 2026. Source: IQAir.
Seattle has recently launched a Low-Pollution Neighborhoods program focused on improving air quality and climate-related issues in more polluted areas, particularly in communities along the lower Duwamish River (4). Given these areas can have problems idling trucks at the port emitting nitrogen oxides, the city is working to replace older diesel trucks with cleaner delivery systems.
4. Melbourne, Australia
Melbourne, Australia’s annual average PM2.5 concentration is typically low, and since 2021 has consistently met Australia’s national standard of 7 µg/m3 (5). In 2025, the city’s annual concentration was 4.3 µg/m3. It’s also among three major Australian cities that have ranked as the top five cleanest cities, despite the fact that the country can be prone to bushfires and dust storms.
The 2025-2026 bushfire season was moderate, allowing the city to maintain cleaner air quality until January 2026 (6). Bushfire smoke impacted the skies in Melbourne in January and eventually crossed the Pacific to reach South America.
Victoria’s government, based in the state capital of Melbourne, has committed to increasing renewable electricity generation to 50% by 2030, growing the public transport and zero-emission vehicle fleet, and discouraging residents from using wood heaters in winter (7).
Air quality in Melbourne, Australia on May 14, 2026. Source: IQAir.
3. Auckland, New Zealand
Auckland, New Zealand continues to benefit from New Zealand’s geographical isolation and coastal winds. In 2025, Auckland had an annual average PM2.5 concentration of 4.3 µg/m3, the same concentration as Melbourne. The city’s annual average is generally under the WHO guideline, though there are concerns about potential future increases due to policy changes.
Like most of the cities on this list, Auckland is near the ocean; enjoying two natural, large harbors, fresh air and isolation from other manufacturing centers provides some air quality advantages. The city also receives 1167 mm of rainfall annually, which can help remove larger airborne particles from the atmosphere more quickly, like PM10, (particulate matter measuring 10 micrometers or smaller.)
Air quality in Auckland, New Zealand on May 12, 2026. Source: IQAir.
Air quality improvement efforts in Auckland have been ongoing over several years. The city was the cleanest major city in 2024, in part through policies supporting electric vehicles and expanded air quality monitoring to improve public awareness and source mitigation (8).
Air quality policy changes and trends could prove more challenging in the city’s future. While 4.3 µg/m3 is within the World Health Organization’s recommended guideline, it is an uptick from 2024 and 2023 when the annual average PM2.5 concentration was 3.3 and 3.4 µg/m3 respectively.
Activists sued the government in 2025, citing the fact that the government had eliminated 35 climate policies, including a decarbonization plan for industry and a discount for clean energy vehicles (9). In 2026, the government also amended climate laws to shield companies from being sued for greenhouse gas emissions (10).
2. Sydney, Australia
Sydney, Australia’s air quality remained healthy, with a 2025 annual average PM2.5 concentration of 3.9 µg/m3. The city has met the World Health Organization’s air quality guideline for the past four years.
Australia’s largest city and the capital of New South Wales, Sydney can be affected by bushfires and hazard reduction burns. For instance, the extreme bushfire season of 2019-2020 resulted in the city’s annual average PM2.5 for 2019 being 10.1 µg/m3.
However, the coastal city has taken many proactive steps to maintain clean air quality. Sydney’s bus fleet is expected to be fully electric by 2035 (11). Older vehicles which emit more emissions are also being phased out in the city in favor of EV vehicles.
Air quality in Sydney, Australia on May 12, 2026. Source: IQAir.
1. Canberra, Australia
The cleanest major city in the world for 2025 was Canberra, the capital city of Australia. The city’s annual average PM2.5 concentration was 3.6 µg/m3. In 2024, Canberra was the second cleanest major city in the world; it overtook Auckland as the city with the healthiest air quality in 2025.
Though located inland, Canberra is just 65 kilometers from the Pacific coast. This allows it to benefit from pollutant-dispersing breezes, while its relatively small population and limited industrial activity further contribute to its clean air. However, bushfire smoke remains a seasonal challenge, prompting the city to improve air quality monitoring, public alerts, and wood heater emission standards to mitigate impacts.
As Australia’s capital, Canberra both benefits from and contributes to national efforts aimed at reducing air pollution, including strict standards for PM2.5 and efforts to phase out wood heaters, a significant source of winter pollution (12).
Canberra, Sydney, and Melbourne’s success in controlling pollution at its source also reflects Australia’s broader commitment to air quality, with national standards for PM2.5 among the strictest in the world (13).
Air quality in Canberra, Australia on May 12, 2026. Source: IQAir.
Yet, the city’s clean air is not without challenges—wood heater use, bushfires, and dust storms can still cause spikes in PM2.5 concentrations, and ongoing vigilance is required to maintain its leading position. If left unchecked, softening government policies on air quality and environmental law could set back progress made over the years to improve the nation’s air quality. For example, activist groups raised concerns in early 2025 about government efforts to weaken the Environmental Protection and Biodiversity Act (14)(15).
Conclusion
Even in major cities with the cleanest air, no amount of pollution is entirely safe. Sustained action is essential to maintain progress and protect public health. And as has been seen in some cases, shifting policy focus away from emissions reductions can result in fewer wins in the fight for universally clean air.
Monitoring air quality and advocating for cleaner energy and stronger environmental policies can help ensure that these cities remain models of clean air for the world. Their progress demonstrates that cleaner air in major cities is achievable when monitoring, infrastructure, and long-term policy work together.
