Although all cities in Southeast Asia continue to fall short of the World Health Organisation’s (WHO’s) recommended air pollution limits in 2025, the region reached an encouraging collective milestone, according to new data.
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For the first time, every country in Southeast Asia met the WHO’s target for maintaining annual PM2.5 concentrations below 35 micrograms per cubic metre (µg/m³), said air pollution monitoring group IQAir.
PM2.5 refers to airborne particles with a diameter of 2.5 micrometres or smaller that can penetrate deep into the lungs and bloodstream, posing significant health risks.
“Progress was headlined by Laos, Myanmar, Indonesia, Thailand, Malaysia, and Cambodia, all of which continued their year-on-year improvements,” said IQAir in its 2025 World Air Quality Report, published today.
One of the reasons that air pollution levels fell was the La Niña weather phenomenon, which brought substantial rains, intense typhoons, and strong winds to the region, IQAir said in a media statement. The wetter conditions also suppressed agricultural fires that typically contribute to haze.
However, three countries recorded a decline in air quality. “Vietnam and Singapore reported slight increases in pollution levels, while the Philippines saw a sharp 28 per cent rise, with concentrations climbing from 14 µg/m³ in 2024 to 19 µg/m³ in 2025,” the report said.
IQAir told Eco-Business that the main cause for the rise in air pollution in the Philippines was due to several factors, including an expanded monitoring network. Ground level monitors were up 25 per cent in 2025 compared to the year before, and the number of cities covered increased by 50 per cent.
“As air quality monitoring networks expand, they provide a more representative picture of PM2.5 levels by capturing pollution across a wider range of locations,” said Dr Christi Chester Schroeder, IQAir’s senior air quality scientist.
“Air pollution can vary significantly within the same country due to traffic, industry, and local geography, so a limited number of monitors may miss important hotspots or overrepresent cleaner areas. With more monitors, annual averages become more accurate and better reflect the true exposure people experience.”
Indonesia recorded the highest air pollution among Southeast Asian countries in 2025, but recorded a 15 per cent decrease in PM2.5 compared to its 2024 levels. Image: 2025 World Air Quality Report/ IQAir
Of the eight most polluted cities in the Philippines, six of them are new additions to the report. Pasay (42 µg/m³, most polluted city), Quezon City (24.3 µg/m³, third most polluted city), and Marikina (22.7 µg/m³, fifth most polluted city) are all within the five most polluted cities in the Philippines after not being in last year’s report, raising the country’s overall average.
Transboundary concerns
Indonesia remained the worst country for air pollution in the region, despite having shown improvements across several key cities including capital Jakarta. The report said that transportation emissions remains a persistent problem for air quality in large urban centres,
Meanwhile, agricultural burning and wildfires in Indonesia continue to cause transboundary pollution and seasonal spikes in particulate matter.
“Coal-fired power plants, especially pre-2019 facilities near Jakarta, remained a key source of air pollution in parts of the country,” IQAir’s report added.
No Southeast Asian cities met the WHO’s annual PM2.5 guideline in 2025, with nine of the region’s top 15 most polluted cities recorded in Vietnam. (see table)
Hanoi recorded its sixth consecutive year of rising air pollution, with an annual average of 45.9 µg/m³ in 2025. Its residents faced hazardous conditions for nearly a third of the year, with 31 per cent of annual hours exceeding concentrations of 50 µg/m³, IQAir data showed.
“Vietnam’s air quality is impacted by vehicular emissions, coal combustion, and biomass burning,” the report said. The country makes the most cement after China, with cement factories a significant source of PM2.5 pollution.
Outdated motorcycles, coal-fired power plants, and rice straw burning in the Mekong Delta also drove up pollution levels, with indoor cooking and unvented biomass stoves adding to household exposure, IQAir added.
In July 2025, the country’s administration announced a ban on fossil-fuel motorcycles in central Hanoi, which is set to take effect this July as part of a nationwide push to slash urban smog and combat climate change.
Thailand’s government also took measures to combat air pollution last year, as the House of Representatives unanimously passed the Clean Air Act in October. The law guarantees citizens’ right to clean air and imposes strict penalties on polluters.
Nine out of the 15 most polluted cities in Southeast Asia were in Vietnam in 2025. Image: 2025 World Air Quality Report/ IQAir
However, regional challenges remain. Although countries like Malaysia recorded a modest decline in PM2.5 concentration in 2025, it faced its worst transboundary haze crisis in years in July and August due to forest and peatland fires in Indonesia’s Sumatra and Kalimantan.
“Transboundary haze remains a shared struggle for all Southeast Asian nations, signaling that while local improvements are vital, long-term success will depend on sustained international cooperation,” IQAir said.
The air quality monitoring group also highlighted challenges related to the availability and reliability of government-led data.
“While 406 cities in Southeast Asia were included in this year’s Report, fewer than 47 per cent – only 190 cities – were equipped with official government monitoring stations,” the report said.
“This gap underscores a critical need: while policy initiatives to reduce emissions are essential, they must be supported by a robust, well-maintained data network to accurately measure progress and validate environmental outcomes.”
