Visualizing indoor ozone exposures via o-dianisidine based colorimetric passive sampler

In this study, we developed a colorimetric ozone passive sampler (OPS) incorporating o-dianisidine, a redox dye, into a polydimethylsiloxane sheet. The reaction between ozone (O₃) and o-dianisidine result in a visible yellowish color change. Unlike previous passive methods that rely on nitrate extraction or the color disappearance of indigotrisulfonate, the OPS offered improved recognition of average O₃ exposure. To optimize OPS based on time-weighted average (TWA), we extracted and quantified the amount of reacted o-dianisidine after exposing OPS to O₃ by varying concentrations (0–200 ppb) within 8 h. Colorimetric changes of OPS were further analyzed by capturing images, and the effective absorbance of blue scale showed the best fit (EA_B, R² =0.997). OPS validation on visual detection assessed by six parameters: limit of detection, limit of quantification, reproducibility, sampling rate, selectivity to interfering gases, and sensitivity to environmental factors. To enhance visibility, the OPS was assembled with coloration exposure guidelines, and a smartphone app was developed to quantify average O₃ exposures. We further conducted field tests that showed the significant disparity between O₃ concentrations and personal O₃ exposures, which is considered more crucial for assessing health risks. The OPS was optimized to monitor O₃ exposure levels and raise awareness among workers and occupants regarding invisible indoor hazards.