Indoor particulate reactive oxygen species concentrations

- The concentration of ROS on PM2.5 was measured inside and outside 23 buildings.
- Residential and commercial buildings had comparable concentrations.
- Indoor and outdoor concentrations were found to be not significantly different.
- Indoor exposure to particulate ROS likely dominates outdoor exposure.
- First study to simultaneously measure indoor and outdoor ROS on PM2.5.

Despite the fact that precursors to reactive oxygen species (ROS) are prevalent indoors, the concentration of ROS inside buildings is unknown. ROS on PM2.5 was measured inside and outside twelve residential buildings and eleven institutional and retail buildings. The mean (±s.d.) concentration of ROS on PM2.5 inside homes (1.37±1.2 nmoles/m3) was not significantly different from the outdoor concentration (1.41±1.0 nmoles/m3). Similarly, the indoor and outdoor concentrations of ROS on PM2.5 at institutional buildings (1.16±0.38 nmoles/m3 indoors and 1.68±1.3 nmoles/m3 outdoors) and retail stores (1.09±0.93 nmoles/m3 indoors and 1.12±1.1 nmoles/m3 outdoors) were not significantly different and were comparable to those in residential buildings. The indoor concentration of particulate ROS cannot be predicted based on the measurement of other common indoor pollutants, indicating that it is important to separately assess the concentration of particulate ROS in air quality studies. Daytime indoor occupational and residential exposure to particulate ROS dominates daytime outdoor exposure to particulate ROS. These findings highlight the need for further study of ROS in indoor microenvironments.