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SUMMARY:Optical Absorptivity versus Molecular Composition of Model Organic
  Aerosol Matter - Dr Angela-G. Rincon-Benavides
DTSTART:20101025T131500Z
DTEND:20101025T141500Z
UID:TALK25912@talks.cam.ac.uk
CONTACT:Dr Alex Archibald
DESCRIPTION:Aerosol particles affect the Earth’s energy balance by absor
 bing and scattering radiation according to their chemical composition\, si
 ze 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 grou
 ps via high-resolution mass spectrometry although: (1) absorptivity is ass
 ociated with structural chromophores rather than with molecular formulas\,
  (2) compositional space is a small projection of structural space\, (3) m
 ixtures of polar polyfunctional species usually exhibit supramolecular int
 eractions. Here we report a suite of experiments showing that the photolys
 is of aqueous pyruvic acid (a proxy for aerosol alpha-dicarbonyls absorbin
 g at wavelength > 300 nm) generates mixtures of identifiable aliphatic pol
 yfunctional oligomers that develop absorptions in the visible upon standin
 g in the dark. These absorptions and their induced fluorescence emissions 
 can be repeatedly bleached and retrieved without carbon losses or ostensib
 le changes in the electrospray mass spectra of the corresponding mixtures\
 , and display unambiguous signatures of supramolecular effects. The non-li
 near additivity of the properties of the components of these mixtures supp
 orts 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.
LOCATION:Unilever Lecture Theatre\, Department of Chemistry
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