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Published October 1, 2009 | Supplemental Material
Journal Article Open

Optical Absorptivity versus Molecular Composition of Model Organic Aerosol Matter


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 the molecular composition 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, and (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 α-dicarbonyls absorbing at λ > 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 loss or ostensible changes in the electrospray mass spectra of the corresponding mixtures and display unambiguous signatures of supramolecular effects. The nonlinear additivity of the properties of the components of these mixtures supports the notion that full structural speciation is insufficient and possibly unnecessary for understanding the optical properties of aerosol particles and their responses to changing ambient conditions.

Additional Information

Copyright © 2009 American Chemical Society. Received: May 18, 2009; Revised Manuscript Received: July 2, 2009. Publication Date (Web): August 28, 2009. This project was financially supported by the National Science Foundation (ATM-0714329). A.G.R. acknowledges financial support from the Swiss National Science Foundation (PBL2-110274). Note Added After ASAP Publication: This article posted ASAP on August 28, 2009. Figure 4C has been revised. The corrected version posted on September 3, 2009.

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August 19, 2023
October 19, 2023