Maillard-like Reactions Generate Secondary Organic Products with Oxidative Potential: Mechanisms and Photoaging Enhancement.

The formation mechanisms and atmospheric evolution of secondary organic aerosols contributing to the oxidative potential (OP) remain poorly understood, limiting the assessment of their potential health impacts. Here, we demonstrate for the first time that atmospheric aqueous Maillard-like reactions constitute an important pathway for generating secondary organic products with OP. Six representative dicarbonyl-nitrogen reaction systems were designed to systematically investigate the formation kinetics, molecular characteristics, and photoaging evolution of the products generated from the Maillard-like reactions. All reactions systems generated measurable intrinsic OP, with the methylglyoxal-ethylamine system exhibiting the highest intrinsic OP (9.8 ± 0.7 pmol/min/μg). The HULIS fraction was identified as the dominant contributor to OP, while molecular characterization further suggested that nitrogen-containing heterocyclic compounds within this fraction as important contributors to the observed OP. Photoaging further enhanced the intrinsic OP (3.8-42.3 pmol/min/μg) accompanied by an increased abundance of unsaturated chromophores with extended π-conjugation, which may facilitate electron transfer and redox cycling. These findings elucidate a mechanistic framework for understanding how Maillard-like reactions contribute to aerosol oxidative potential, thereby advancing our understanding of their potential health implications.