Identification of the major HO_X radical pathways in an indoor air environment

OH and HO_2 profiles measured in a real environment have been compared to the results of the INCA-Indoor model to improve our understanding of indoor chemistry. Significant levels of both radicals have been measured and their profiles display similar diurnal behavior, reaching peak concentrations during direct sunlight (up to 1.6 × 10^6 and 4.0 × 10^7 cm^(−3) for OH and HO_2, respectively). Concentrations of O_3, NO_X, volatile organic compounds (VOCs), HONO and photolysis frequencies were constrained to the observed values. The HO_X profiles are well simulated in terms of variation for both species (Pearson's coefficients: pOH = 0.55, pHO2=0.76), and concentration for OH (mean normalized bias error: MNBE_(OH) = -30%), HO_2 concentration being always underestimated (MNBE_(HO2) = -62%). Production and loss pathways analysis confirmed HONO photolysis' role as an OH precursor (here up to 50% of the production rate). HO_2 formation is linked to OH-initiated VOCs oxidation. A sensitivity analysis was conducted by varying HONO, VOCs and NO concentrations. OH, HO_2, and formaldehyde concentrations increase with HONO concentrations; OH and formaldehyde concentrations are weakly dependent on NO whereas HO_2 concentrations are strongly reduced with increasing NO. Increasing VOCs concentrations decreases OH by consumption and enhances HO_2 and formaldehyde.