Volatile organic compound conversion by ozone, hydroxyl radicals, and nitrate radicals in residential indoor air: Magnitudes and impacts of oxidant sources.

Indoor chemistry may be initiated by reactions of ozone (O), the hydroxyl radical (OH), or the nitrate radical (NO) with volatile organic compounds (VOC). The principal indoor source of O is air exchange, while OH and NO formation are considered as primarily from O reactions with alkenes and nitrogen dioxide (NO), respectively. Herein, we used time-averaged models for residences to predict O, OH, and NO concentrations and their impacts on conversion of typical residential VOC profiles, within a Monte Carlo framework that varied inputs probabilistically. We accounted for established oxidant sources, as well as explored the importance of two newly realized indoor sources: () the photolysis of nitrous acid (HONO) indoors to generate OH and () the reaction of stabilized Criegee intermediates (SCI) with NO to generate NO. We found total VOC conversion to be dominated by reactions both with O, which almost solely reacted with d-limonene, also with OH, which reacted with d-limonene, other terpenes, alcohols, aldehydes, and aromatics. VOC oxidation rates increased with air exchange, outdoor O, NO and d-limonene sources, and indoor photolysis rates; and they decreased with O deposition and nitric oxide (NO) sources. Photolysis was a strong OH formation mechanism for high NO, NO, and HONO settings, but SCI/NO reactions weakly generated NO except for only a few cases.