First close insight into global daily gapless 1 km PM2.5 pollution, driving factors, and health impact

Abstract Fine particulate matter (PM 2.5 ) is the largest environmental risk factor impacting human health. While PM 2.5 has been measured widely across the world, there has been no high-resolution and gapless global PM 2.5 data on a daily scale. We generate a global daily PM 2.5 concentration at 1 km resolution using satellite gap-filled aerosol products and machine learning. Daily PM 2.5 retrievals agreed well with ground measurements, with sample-, space-, and time-based cross-validated correlations of 0.93, 0.89, and 0.88, respectively. This enables us to unprecedentedly monitor the day-to-day variations of PM 2.5 , exposure risk, and mortality burden around the globe. More than 96% of the days exceeded the World Health Organization (WHO) recommended daily air quality guidelines (AQG) level (15 μg m -3 ) in 2020, and 99% of populated areas were exposed to PM 2.5 risk at least one day; in particular, the proportions are 91% and 64% similarly in 7 and 30 days, respectively. The annual population-weighted mean PM 2.5 concentration was 27.6 μg m -3 (~5.5 times higher than the WHO annual AQG level of 5 μg m -3 ), resulting in estimated premature deaths of ~4.2 million people and accounting for ~6.6% of total global deaths. Substantial differences are noted in many parts of the world between 2019 and 2020 associated with widespread episodes of wildfires or the COVID-19 shutdowns. The overall air quality in 2020 was significantly better than in 2019 in more than 70% of major cities. The global population-weighted mean PM 2.5 decreased by ~5.1%, and the associated number of premature deaths dropped by 56,700.