Association of PILS-based and filter-based particle-bound reactive oxygen species with urban nanoparticles, secondary organic aerosols, and in-vitro oxidative responses

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-ROS₍filter₎.