The team found that only 0.18% of the global land area and 0.001% of the global population are exposed to levels of PM2.5 below those recommended by the World Health Organization (WHO).
Faced with a lack of monitoring stations in some areas of the world, the team also used satellite-based meteorological and air pollution detectors as well as statistical and machine learning methods to map global changes in pm2.5 over the two decades until 2019.
Team leader Professor Yuming Guo said, “In this study, we used an innovative machine learning approach to integrate multiple meteorological and geological information to estimate the global surface-level daily PM2.5 concentrations at a high spatial resolution of approximately 10km×10km for global grid cells in 2000-2019, focusing on areas above 15 µg/m³ which is considered the safe limit by WHO.”
Apart from the headline figures above, the study found that over the 20 year period, levels fell in Europe and North America while they rose in Southern Asia, Australia, New Zealand, Latin America and the Caribbean. The global trend was slightly downwards but by 2019, 70% of days saw levels above 15 µg/m³. This figure was 90% in Southern and Eastern Asia.
In other findings, the annual average PM2.5 around the world from 2000 to 2019 was 32.8 µg/m3. The highest PM2.5 concentrations were in Eastern Asia (50.0 µg/m3) and Southern Asia (37.2 µg/m3), followed by northern Africa (30.1 µg/m3).
Professor Guo added that the study, “provides a deep understanding of the current state of outdoor air pollution and its impacts on human health. With this information, policymakers, public health officials, and researchers can better assess the short-term and long-term health effects of air pollution and develop air pollution mitigation strategies.”
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