Abstract
Ambient air pollutants are leading contributors to global mortality. Despite the well-established risks, most studies have relied on single-pollutant models in limited regions, leaving the combined effects and individual contributions of pollutants unclear, particularly across countries. Here, we integrate daily mortality and air pollutant (nitrogen dioxide [NO(2)], ozone [O(3)], fine particulate matter, and sulfur dioxide) data from 482 cities in 12 countries/territories from 1998 to 2021 to assess the joint mortality risks and identify the main contributing pollutant through an air quality health index of multi-pollutant constrained groupwise additive models (AQHI-Multi). AQHI-Multi outperformed commonly used air quality indices in capturing the overall mortality risks. O(3) and NO(2) were the leading contributors (accounting for over 70% across countries/territories), with O(3)'s share increasing slightly to moderately in most countries/territories. These findings highlight the need for developing air quality indices using advanced multi-pollutant models and the emerging global significance of targeted control of O(3) and NO(2).