Toward Better and Healthier Air Quality: Global PM 2.5 and O 3 Pollution Status and Risk Assessment Based on the New WHO Air Quality Guidelines for 2021.

To reduce the high burden of disease caused by air pollution, the World Health Organization (WHO) released new Air Quality Guidelines (AQG) on September 22, 2021. In this study, the daily fine particulate matter (PM 2.5 ) and surface ozone (O 3 ) data of 618 cities around the world is collected from 2019 to 2022. Based on the new AQG, the number of attainment days for daily average concentrations of PM 2.5 (≤ 15 µg m -3 ) and O 3 (≤ 100 µg m -3 ) is approximately 10% and 90%, respectively. China and India exhibit a decreasing trend in the number of highly polluted days (> 75 µg m -3 ) for PM. Every year over 68% and 27% of cities in the world are exposed to harmful PM 2.5 (> 35 µg m -3 ) and O 3 (> 100 µg m -3 ) pollution, respectively. Combined with the United Nations Sustainable Development Goals (SDGs), it is found that more than 35% of the world's cities face PM 2.5 -O 3 compound pollution. Furthermore, the exposure risks in these cities (China, India, etc.) are mainly categorized as "High Risk", "Risk", and "Stabilization". In contrast, economically developed cities are mainly categorized as "High Safety", "Safety", and "Deep Stabilization." These findings indicate that global implementation of the WHO's new AQG will minimize the inequitable exposure risk from air pollution.