Is air pollution mitigation enough? When adaptation is needed to protect health

The 2021 update to the World Health Organization (WHO) Global Air Quality Guidelines (AQGs) for Fine Particulate Matter (PM_2.5) presents ambitious targets that may not be achievable worldwide by 2030 and beyond. Regions influenced by biogenic sources, hard-to-abate sectors, or unique orographic and meteorological conditions may face persistent challenges to meet healthy targets. This research aims to evaluate the feasibility of the WHO’s AQGs for PM_2.5 on a global scale based on recent historical data, complementing evidence from simulations. Through a comprehensive review of the existing literature and analysis of recent data, we use a variety of methods to show that natural sources and background concentration levels of PM_2.5 constitute a significant share of overall concentrations and a source of inequality in exposure. Our study includes reanalysis data, high-resolution empirical estimates, and measurements from ground-level monitoring stations around the world. Using 1-km data we analyze inequality in exposure to air pollution across age, gender and income. We find that the recommended AQGs are widely exceeded globally, and show substantial heterogeneity between regions. Exceedances are particularly pronounced in many parts of Asia and Africa, where populations are exposed to unhealthy PM_2.5 levels for most of the year. In roughly a third of the analyzed areas, desert dust and sea salt aerosols alone cause exceedances of the guidelines, indicating that mitigation is not sufficient and adaptation is required. Globally, only a small share of the population currently breathes air within the recommended limits, yet we find that spatial resolution matters when assessing exposure. Income is the main source of inequality in exposure, while differences by age and gender are minimal when considering ambient air levels.