Global Fine-Scale Acute Exposure to Ambient Nitrogen Dioxide (NO2)

Acute exposure to surface nitrogen dioxide (NO ₂ ) poses substantial health risks worldwide. Using advanced machine learning techniques, we retrieved the first global, daily, gap-free surface NO ₂ data at 1-km resolution from downscaled TROPOMI satellite observations since its launch to 2022. Global NO ₂ exhibited pronounced day-to-day variability, with population-weighted values ranging from 11.8 to 23.7 µg m ^− 3 , representing daily fluctuations of up to 73% relative to the mean level of 16.4 µg m ^− 3 . China (23%) and India (18%) contribute most significantly to global NO ₂ exposure. Although only 28% of inhabited areas experience daily NO ₂ concentrations exceeding the World Health Organization’s short-term air quality guideline of 25 µg/m ³ for at least one day within the year, these exceedances disproportionately affect over 61% of the global population. This disparity is especially pronounced in densely populated megacities, where 98% experience at least one day of unhealthy air quality per year. The proportion remains high (77% and 56%) when extending the threshold to 7-day and 30-day exceedances, respectively. We estimate that acute NO ₂ exposure contributed to approximately 576,000 (95% CI: 473,000–678,000) premature deaths globally in 2019, while the chronic mortality burden was roughly five times higher, at 2,688,000 (95% CI: 702,000–3,921,000). The strictest COVID-19 pandemic lockdowns implemented in 2020 caused widespread temporary declines in NO ₂ levels globally, followed by rebounds as restrictions eased in 91% of countries by 2022; however, 59% of countries have maintained NO ₂ levels below 2019 pre-pandemic baselines. Our findings underscore the significant yet often under-recognized risks posed by acute NO ₂ exposure, highlighting the urgent need for comprehensive and detailed global exposure assessment to inform the design of effective public health and environmental policies.