Aerosol Composition Trends during 2000–2020: In depth insights from model predictions and multiple worldwide observation datasets

Abstract. Atmospheric aerosols significantly impact Earth’s climate and air quality. In addition to their number and mass concentrations, their chemical composition influences their environmental and health effects. This study examines global trends in aerosol composition from 2000 to 2020, using the EMAC atmospheric chemistry-climate model and a variety of observational datasets. These include PM_2.5 data from regional networks and 744 PM₁ datasets from AMS field campaigns conducted at 169 sites worldwide. Results show that organic aerosol (OA) is the dominant fine aerosol component in all continental regions, particularly in areas with significant biomass burning and biogenic VOC emissions. EMAC effectively reproduces the prevalence of secondary OA but underestimates the aging of OA in some cases, revealing uncertainties in distinguishing fresh and aged SOA. While sulfate is a major aerosol component in filter-based observations, AMS and model results indicate nitrate predominates in Europe and Eastern Asia. Mineral dust also plays a critical role in specific regions, as highlighted by EMAC. The study identifies substantial declines in sulfate, nitrate, and ammonium concentrations in Europe and North America, attributed to emission controls, with varying accuracy in model predictions. In Eastern Asia, sulfate reductions due to SO₂ controls are partially captured by the model. OA trends differ between methodologies, with filter data showing slight decreases, while AMS data and model simulations suggest slight increases in PM₁ OA across Europe, North America, and Eastern Asia. This research underscores the need for integrating advanced models and diverse datasets to better understand aerosol trends and guide environmental policy.