Brown carbon (BrC) components of biomass burning organic aerosol (BBOA) absorb sunlight at visible wavelengths. However, it is not clear whether the total light absorption of this BrC is simply the sum of the contributions of the individual components or whether the components can bind noncovalently to give additional absorption through charge transfer. Here, intermolecular interactions between guaiacol and quinones (1,4-benzoquinone and 1,4-naphthoquinone) were identified in proxies of the nonpolar, water-insoluble phase of BBOA, using UV-vis spectroscopy. Guaiacol and its derivatives are some of the most abundant emissions of smoldering coniferous species. Enhanced light absorption occurred instantaneously upon mixing colorless guaiacol with either quinone in