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

摘要

Indoor chemistry may be initiated by reactions of ozone (O_3), the hydroxyl radical (OH), or the nitrate radical (NO_3) with volatile organic compounds (VOC). The principal indoor source of O_3 is air exchange, while OH and NO_3 formation are considered as primarily from O_3 reactions with alkenes and nitrogen dioxide (NO_2), respectively. Herein, we used time-averaged models for residences to predict O_3, OH, and NO_3 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: (ⅰ) the photolysis of nitrous acid (HONO) indoors to generate OH and (ⅱ) the reaction of stabilized Criegee intermediates (SCI) with NO_2 to generate NO_3. We found total VOC conversion to be dominated by reactions both with O_3, which almost solely reacted with D-limonene, and also with OH, which reacted with D-limonene, other terpenes, alcohols, aldehydes, and aromatics. VOC oxidation rates increased with air exchange, outdoor O_3, NO_2 and D-limonene sources, and indoor photolysis rates; and they decreased with O_3 deposition and nitric oxide (NO) sources. Photolysis was a strong OH formation mechanism for high NO, NO_2, and HONO settings, but SCI/NO_2 reactions weakly generated NO_3 except for only a few cases.