Global air pollution worsened in 2025 as Thailand ranked 48th worst

Global air quality deteriorated in 2025, with just 14% of cities worldwide meeting the World Health Organization’s annual PM2.5 guideline, down from 17% a year earlier, according to IQAir’s latest World Air Quality Report.

The report highlighted how a combination of persistent human-caused pollution and climate-related extremes continued to worsen air quality across many regions. Wildfires and dust storms were among the major factors behind the deterioration, with climate change helping to intensify both the frequency and severity of such events.

Thailand was ranked 48th among the world’s most polluted countries in 2025, with an average PM2.5 concentration of 17.8 micrograms per cubic metre. That was an improvement from 19.8 micrograms per cubic metre a year earlier, but still well above the WHO guideline of 5 micrograms per cubic metre.

IQAir’s country rankings showed Pakistan as the world’s most polluted country in 2025, with an annual average PM2.5 level of 67.3 micrograms per cubic metre, followed by Bangladesh at 66.1, Tajikistan at 57.3, Chad at 53.6 and the Democratic Republic of the Congo at 50.2. India ranked sixth at 48.9.

South Asia remained the world’s most polluted region, while New Delhi continued to rank among the most polluted capitals globally. IQAir said many of the worst readings were linked to a mix of transport emissions, industrial activity, construction dust and other combustion sources.

The report also underscored how transboundary pollution remains a persistent problem in East and Southeast Asia, where smoke from fires and industrial emissions can cross borders and undermine local clean-air efforts. IQAir said meaningful progress depends not only on national action but also on regional cooperation.

Within Thailand, the highest average PM2.5 levels were recorded in Om Noi Municipality in Samut Sakhon at 32.2 micrograms per cubic metre, followed by Map Ta Phut Municipality in Rayong at 27.9 and Wiang Phang Kham in Chiang Rai at 27.8, according to the report data cited in the source text. At the other end of the scale, some parts of the world still maintained air quality within WHO limits, with French Polynesia among the cleanest at 1.8 micrograms per cubic metre.

Air pollution remains one of the world’s most serious environmental health risks. The WHO estimates that ambient, or outdoor, air pollution causes 4.2 million premature deaths a year worldwide, largely through cardiovascular disease, respiratory illness and cancers linked to exposure to fine particulate matter.

Frank Hammes, IQAir’s global chief executive, said the findings showed how vulnerable air quality remains without sustained action. “Air quality is a fragile asset that requires active stewardship to protect public health,” he said. He added that without monitoring, it is impossible to fully understand what people are breathing, and said wider access to real-time data, lower emissions and stronger climate action were essential to achieving lasting improvements in air quality.

The economic toll is also vast. The World Bank has estimated that the global damage from air pollution runs into trillions of dollars annually, with widely cited figures putting the cost at roughly US$4.5 trillion to US$6.1 trillion, or up to around 6.5% of global GDP.

The worsening picture in 2025 has renewed calls for stronger international action, particularly on reducing fossil fuel use, controlling open burning and improving air-quality monitoring. IQAir and health experts say cleaner air will depend on sustained local, national and cross-border measures, especially as climate change makes pollution episodes harder to predict and more damaging when they occur.