In 2025, the East Asia region was represented by 1,264 cities across seven countries and regions. Air PM2.5 concentrations compared to 2024, while 312 unchanged. At the national level, annual average concentrations rose in two countries and fell in five. Japan saw the largest relative increase, climbing 14% to 9.8 μg/m3. Conversely, Mongolia showed significant progress with a 31% decrease, dropping from 25.6 μg/ Despite these shifts, no country in the region met the Range of 2025 average PM2.5 (μg/m3) across regional cities WHO annual guideline. China recorded the highest national average at 29.6 μg/m3, a very slight drop from the 2024 average of 31 μg/m3 and continues to remain nearly six times the WHO annual guideline value. Most The regional extremes, cities with the highest and lowest PM2.5 annual concentrations, were both found in China. Hotan remained the most polluted city with an average of 109.6 μg/m3, while Ngari recorded the region's lowest concentration at 5.3 μg/m3, narrowly missing the WHO annual guideline. This is the second in East Asia in 2025. China contributed the largest number of new cities, with seven additions, followed by South Korea and Japan with four each. Among these new entries, Japan provided data for the four cities with the lowest annual average PM2.5 concentrations, all of which were below 15 μg/m3. Government-operated regional data, reflecting the highest proportion of