Oxidative Potential from Common Indoor Sources of Particulate Matter

Although people spend nearly 90% of their time indoors, the source-specific oxidative potential (OP) from indoor emissions spanning multiple particle generation mechanisms is largely unknown. Here, we quantify the OP of the PM originating from commonly used indoor sources via three different assays, i.e., dithiothreitol consumption (OP_DTT), glutathione consumption (OP_GSH), and hydroxyl radical generation (OP_OH). The intrinsic (mass-normalized) OP^m of several sources (candles, incense, cigarettes, humidifiers using tap water, toasters, and air fryers) were comparable (0.75-1.25×) or exceeded (1-6×) that of typical ambient PM_2.5. Emissions from candles in the presence of a wind-draft had the highest OP_DTT^m and OP_OH^m while OP_GSH^m was highest for cigarette emissions. Elemental carbon determined the OP of PM emitted from sources undergoing incomplete combustion, whereas, for noncombustion sources (water evaporation and heating-based), metals were the important drivers. An exploratory exposure assessment in a hypothetical apartment (volume = 100 m³, air change rate = 0.45 h^-1, and penetration coefficient = 0.6) revealed that certain sources (e.g., incense, cigarettes, toasters, and air-fryers) could result in occupants being exposed to higher OP in less than 1 h of indoor operation than that resulting from inhaling typical U.S. ambient PM_2.5 (8 μg/m³) over an entire day. Collectively, these results demonstrate the importance of indoor emissions, emphasizing the need for more comprehensive health impact assessments to assist in the development of policy recommendations aimed at mitigating indoor PM exposure.