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

Abstract Fine particulate matter (PM2.5) is the largest environmental risk factor impacting human health. While PM2.5 has been measured widely across the world, there has been no high-resolution and gapless global PM2.5 data on a daily scale. We generate a global daily PM2.5 concentration at 1 km resolution using satellite gap-filled aerosol products and machine learning. Daily PM2.5 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 PM2.5, 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 PM2.5 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 PM2.5 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 PM2.5 decreased by ~5.1%, and the associated number of premature deaths dropped by 56,700.