Exposures to fine particulate matter (PM₁) have been associated with health impacts, but our understanding of PM₁ concentration-response (PM₁-CR) relationships remains incomplete. This study investigates the association between particulate-bound reactive oxygen species (PB-ROS) and cellular oxidative stress responses induced by urban nanoparticles. PB-ROS were measured using the DCFH assay, both on PTFE filters (24-hour resolution, PB-ROS_filter) and PB-ROS measured using a Particle-Into-Liquid Sampler (2-hour resolution, PB-ROS_PILS). We compared these with oxidative stress markers in BEAS-2B human cell lines exposed directly to ambient air at the air-liquid interface. A comparative analysis of PB-ROS_filter and PB-ROS_PILS revealed significant differences in the types of PB-ROS detected, mainly due to the temporal resolution of sampling and the measurement techniques. In most cases, PB-ROS_filter levels were reduced by more than 90% compared to PB-ROS_PILS. PB-ROS_filter predominantly identified long-lived species, which are more stable and indicative of aged aerosols. In contrast, PB-ROS_PILS provided insights into transient PB-ROS, which correlated with urban nanoparticles. A low condensation sink played a decisive role, suggesting atmospheric conditions in which condensable compounds (including ROS) did not rapidly deposit onto pre-existing accumulation-mode particles but instead bound to nanoparticles. Finally, we demonstrate that gene expression patterns for oxidative stress in BEAS-2B human cell lines correlate with PB-ROS_PILS, but not with PB-ROSfilter.

Addressing the planetary crisis associated with climate change, biodiversity loss, global pollution, and public health requires novel and holistic approaches. Here, we present the methodology and initial results of an experiment conducted in Rome within the framework of the National Biodiversity Future Center (NBFC) project, Spoke 6. The major objective of this study was to outline the planetary health approach as a lens to assess urban health. This transdisciplinary case study explored the relationship between urban traffic-related external exposome and pro-oxidative responses in humans and plants. This methodology is based on the integration of atmospheric dynamics modeling, state-of-the-art aerosol measurements, biomonitoring in human cohorts, in vitro cellular assays, and the assessment of functional trait markers in urban trees. The results indicate that short-term exposure to urban aerosols, even at low concentrations, triggers rapid oxidative and inflammatory responses in bronchial epithelial cells, modulates gene and miRNA expression, alters gut microbiota diversity, and induces functional trait changes in urban trees. This study also highlights the feedback mechanisms between vegetation and atmospheric conditions, emphasizing the role of urban greenery in modulating microclimate and exposure. The methodology and initial results presented here will be further analyzed in future studies to explore proof of a cause–effect relationship between short-term exposure to traffic-related environmental stressors in urban areas and oxidative stress in humans and plants, with implications for chronic responses. In a highly urbanized world, this evidence could be pivotal in motivating the widespread implementation of planetary health approaches for assessing urban health.