Abstract

Aerosol particles affect the Earth’s energy balance by absorbing and scattering radiation according to their chemical composition, size and shape. It is generally believed that their optical properties could be deduced from their molecular composition, particularly of the complex organic matter contained in these particles, a goal pursued by many groups via high-resolution mass spectrometry although: (1) absorptivity is associated with structural chromophores rather than with molecular formulas, (2) compositional space is a small projection of structural space, (3) mixtures of polar polyfunctional species usually exhibit supramolecular interactions. Here we report a suite of experiments showing that the photolysis of aqueous pyruvic acid (a proxy for aerosol alpha-dicarbonyls absorbing at wavelength > 300 nm) generates mixtures of identifiable aliphatic polyfunctional oligomers that develop absorptions in the visible upon standing in the dark. These absorptions and their induced fluorescence emissions can be repeatedly bleached and retrieved without carbon losses or ostensible changes in the electrospray mass spectra of the corresponding mixtures, and display unambiguous signatures of supramolecular effects. The non-linear additivity of the properties of the components of these mixtures supports the notion that even full structural speciation is insufficient, and possibly unnecessary for understanding the optical properties of aerosol particles, and their responses to changing ambient conditions.