Predicting the importance of oxidative aging on indoor organic aerosol concentrations using the two-dimensional volatility basis set (2D-VBS).

Organic aerosol (OA) is chemically dynamic, continuously evolving by oxidative chemistry, for instance, via hydroxyl radical (OH) reactions. Studies have explored this evolution (so-called OA aging) in the atmosphere, but none have investigated it indoors. Aging organic molecules in both particle and gas-phases undergo changes in oxygen content and volatility, which may ultimately either enhance or reduce the condensed-phase OA concentration (COA ). This work models OH-induced aging using the two-dimensional volatility basis set (2D-VBS) within an indoor model and explores its significance on COA relative to prior modeling methodologies which neglect aging transformations. Lagrangian, time-averaged, and transient indoor simulations were conducted. The time-averaged simulations included a Monte Carlo procedure and sensitivity analysis, using input distributions typical of U.S. residences. Results demonstrate that indoors, aging generally leads to COA augmentation. The extent to which this is significant is conditional upon several factors, most notably temperature, OH exposure, and OA mass loading. Time-averaged COA was affected minimally in typical residences (<5% increase). However, some plausible cases may cause stronger COA enhancements, such as in a sunlit room where photolysis facilitates significant OH production (~20% increase), or during a transient OH-producing cleaning event (~35% peak increase).