Oxidative Potential of Particles at a Research House: Influencing Factors and Comparison with Outdoor Particles.

The oxidative potential (OP) of particles can be represented by the ability of particles to generate hydroxyl radicals in an aqueous solution which can be measured with electron paramagnetic resonance (EPR) spectrometry. The oxidative potential of particles may be a more health-relevant metric than other physicochemical properties of particles. While OPEPR has been measured in several outdoor locations, it remains largely unstudied in indoor environments. Total suspended particle samples were collected at an unoccupied research house in eighteen four-day sampling events. The OPEPR of indoor particles was found to be 59 % ± 30 % of the OPEPR of outdoor particles on a sampling volume basis during normal indoor conditions in eight sampling events. However, OPEPR per particle mass was 3.5 ± 0.62 times higher indoors than outdoors, indicating that reactions taking place indoors likely increase OPEPR of indoor particles. In ten sampling events, indoor temperature, relative humidity (RH), air change rate (λ), and cooking activities were varied. OPEPR of indoor particles was found to be significantly influenced (in order of importance) by indoor RH, λ, and temperature. OPEPR of indoor particles was higher than OPEPR for outdoor particles when indoor RH and λ were increased. The presence of cooking activities did not appear to consistently increase OPEPR of indoor particles.