PM2.5 annual average (μg/m3) over 5 years City markers indicating 2025 PM2.5 levels, size adjusted for population Annual average PM2.5 levels in Thailand dropped to 17.8 μg/m3 in 2025, the lowest PM2.5 level in the last five years for the Southeast Asian country. Despite the overall improvement, peak pollutionmonths continue to pose significant publichealth risk.InJanuary2025,20% of reporting cities across the country reported monthly PM2.5 averages exceeding 50 μg/m, more than ten aow Aa pains sanai sd enuer yoyueg u auaina s'd jenuue Om u sw than 23% relative to 2024, as emissions from transportation and industrial activities converged uonid u aids si sud buunns woy buinui suossue buung sog ym triggered emergency measures, including school closures and crop burning bans.35 Despite elevated PM2.5 concentrations during the first three months of 2025, the capital ultimately achieved a 7% reduction in its annual average compared to the previous year, ending 2025 with by La Nina conditions-led to a significant decrease in fre activity and a reduction inmonthly PM2.5averagesacrossthcountryDespittheelateearprovementsthverallolltn levels remained high enough that no city in Thailand successfully met the WHO annual guidelines. Thailand's air quality challenges persisted in 2025, particularly in the northern provinces and Bangkok. Biomass burning—agricultural residues, forest fires, and sugarcane “black snow"- remained the dominant source of PM2.5 in the north and in Bangkok, alongside vehicular emissions, transboundary haze, and industrial pollution.37,3839 Additionally, a significant source When crop burning smoke forced school closures in January 2025, Thai government instructed provincial authorities to enforce the existing ban on stubble crop burning and report how many In October 2025, Thailand's House of Representatives unanimously passed the Clean Air Act, civil society, political parties, and a special vetting panelintroduced a “polluter pays" principle, economic incentives for cleaner practices, and decentralized authority for local governments to Annual hours spent at different PM2.5 pollution levels