Brown carbon (BrC) is a key light-absorbing component of atmospheric aerosols, yet its sources, particularly those driven by aqueous-phase chemistry, remain poorly constrained, leading to an underestimation of its contribution. Here, we demonstrate efficient nitration and hydroxylation of naphthalene under atmospheric aqueous-phase conditions in the presence of HONO and simulated sunlight, yielding two BrC-active products: 2-nitro-1-naphthol and 1-nitronaphthalene. Contrary to prevailing assumptions, 2-nitro-1-naphthol is the dominant product under atmospherically relevant conditions, whereas 1-nitronaphthalene forms only at elevated solute levels characteristic of aerosol liquid water. The OH-initiated nitration mechanism is elucidated by combining macroscopic kinetic modeling with DFT-based thermochemical calculations, revealing the catalytic role of HONO and the importance of aqueous-phase stabilization of key intermediates. By integrating degradation kinetics (kappOH), pathway-specific formation rates (kNOH and kNN), and time-resolved absorbance data, we derive BrC mass absorption coefficients (MACs) of 0. 8–20. 7 m2 g–1. These values exceed those reported for gas-phase naphthalene nitration, highlighting the importance of aqueous-phase aromatic chemistry for atmospheric radiative forcing.
Vidović et al. (Mon,) studied this question.