Europe-Wide Spatial Models for Ultrafine Particles Based on Mobile Monitoring

There is an unmet need for large-scale multicenter studies on health effects of long-term exposure to ultrafine particles (UFPs). Such studies have been hampered by the lack of high-resolution models covering large geographical areas. This study aims to develop and evaluate Europe-wide UFP models using mobile measurements. Between 2018 and 2024, we conducted UFP mobile measurement campaigns in nine European areas. We developed both Europe-wide pooled and area-specific models of UFP concentrations at a 25 m spatial scale, using supervised linear regression with a deconvolution approach. The performance of our pooled models, with and without deconvolution, was similar, exhibiting an overall R² of 0.33-0.36, 0.34-0.35 in 5-fold cross-validation (CV), and 0.29 in leave-one-area-out CV. When evaluated against external independent, longer term off-road measurements collected from seven areas and countries, our deconvoluted model effectively captured UFP variability in both urban and rural settings, with R² ranging from 0.25 to 0.70, modestly better than the non-deconvoluted model (R² = 0.23-0.67) and superior to area-specific models (R² = 0.15-0.42). These findings underscore the ability of our pooled deconvoluted Europe-wide UFP model to capture the variability of UFP across diverse environments. The UFP model estimates will facilitate large-scale multicenter studies to investigate the long-term health effects of UFP exposure.