Association between particle-bound reactive oxygen species and in-vitro oxidative responses induced by traffic-related urban nanoparticles

Exposure to fine particulate matter (PM1) has been associated with health impacts, but understanding the PM1 concentration-response (PM1-CR) relationships remains incomplete, especially at low PM1. Here, we present data related to the RHAPS experiment, carried out in the Po Valley in 2019 [Costabile et al., 2023]. The study investigates the association between particle-bound reactive oxygen species (PB-ROS) and in-vitro oxidative responses induced by exposure to urban nanoparticles. To mimic lung exposure to ambient air, we employed an air-liquid interface (ALI) model using cultures of human bronchial epithelial cells (BEAS-2B). PB-ROS were measured using the DCFH assay via two approaches: offline 24-hour resolution measurements from PTFE filters (PB-ROSfilter) and semi-continuous (2-hour resolution) measurements using a Particle-Into-Liquid Sampler (PILS) (PB-ROSPILS). A comparative analysis of PB-ROSfilter and PB-ROSPILS showed significant differences in the types of ROS detected, primarily driven by the sampling resolution. PB-ROSfilter measurements predominantly identified long-lived species, which are more stable and indicative of aged aerosols, associated with secondary organic aerosols (SOA). In contrast, PB-ROSPILS measurements revealed transient PB-ROS related to urban nanoparticles, which are abundant during the day due to traffic emissions and photochemical processes. Statistically significant correlations suggest that transient PB-ROS are influenced by traffic nanoparticles, with the Condensation Sink (CS) playing a determining role in their persistence in the atmosphere. The CS indicates atmospheric conditions when condensable compounds (including ROS) do not sink rapidly onto pre-existing accumulation-mode particles and may be scavenged by or form nanoparticles [Costabile et al., 2023]. This result suggests that, at high CS values, ROS rapidly condenses onto aged aerosol particles and are depleted in the process. Conversely, at low CS values, ROS is less likely to condense quickly, thus remaining in the atmosphere at higher concentrations [Di Iulio et al., 2025]. Finally, the study highlights a positive correlation between mass-normalized PB-ROSPILS and oxidative stress gene expression, as shown in Figure 1, underscoring the potential health implications of transient ROS species associated with urban nanoparticles. The study's limitations relate to the limited temporal coverage of PILS and the absence of fully online ROS detection methods to characterize highly reactive species, which may pose immediate health risks in urban environments with fresh emissions.