PM2.5 annual average (μg/m3) over 5 years City markers indicating 2025 PM2.5 levels, size adjusted for population In 2025, Vietnam's air quality continued to deteriorate as the annual average PM2.5 concentrations climbed to 29.7 μg/m3, a 4% increase from 2024. The situation was with an annual average of 45.9 μg/m3. In the capital, residents faced hazardous conditions for nearly a third of the year, with 31% of annual hours exceeding concentrations of 50 μg/m3. These spikes peaked in January, with a monthly average of 96.2 μg/m3. Meteorological factors such as cold temperature, low wind speed, during cold conditions contribute to elevated PM2.5 levels in January, the coldest month of the year in Hanoi.46 Vietnam's air quality is impacted by vehicular emissions, coal combustion, and biomass burning.47 Construction and road dust, industrial activities, and transboundary haze exacerbated seasonal smog. Outdated motorcycles, coal-fired power plants, and rice straw burning in the Mekong Delta drove winter spikes, with indoor cooking and unvented biomass stoves adding to household exposure.48.49 noo an u s'd jo ans sis e ae sn s oo warnings were issued in January and March for Hanoi as poor air quality spiked, prompting school closures, and work slowdowns.50 In July 2025, Vietnam announced a groundbreaking ban on fossil-fuel motorcycles in central Hanoi. The ban is set to take effect in July 2026 as part of a nationwide push to slash urban smog and combat climate change.51 The directive, issued by Prime transport, compared to just over 1 million cars) within the main ring road. A second phase set for 2028 will expand the ban and restrict some gasoline cars. The plan also i o pe ui so i (t ona) ss oissa s sn by 2027, low-emission zones, an accelerated plan to shift to electric vehicles (EVs), Annual hours spent at different PM2.5 pollution levels