AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Spectroscopy of Cloud-Processed Aerosols: Glyoxal Oligomers
SARAH D. BROOKS, Elena Avzianova, Texas A&M University
Abstract Number: 587 Working Group: Aerosol Chemistry
Abstract Quantifying the formation of secondary organic aerosol products in evaporating cloud droplets is a challenge, since reactions occurring in a water-restricted environment do not necessarily proceed by the same mechanisms as those which occur when water is readily available. Raman microscopy and Attenuated Total Reflectance Fourier Tranform Infrared Spectroscopy were utilized to facilitate investigations of equilibria between various hydrated and oligomeric forms of glyoxal in aqueous glyoxal solution droplets. The assignment of spectra is obtained through density functional quantum chemical calculations of vibrational wavenumbers, Raman activities, and infrared intensities. Several forms of glyoxal derivatives with similar functional groups, e.g., hydroxyl and dioxolane rings, are found to be present. The absence of a Raman spectral peak corresponding to the vibrational carbonyl stretch provides evidence that both carbonyl groups of a glyoxal molecule become hydrated in solutions of a broad concentration range. The presence of bands corresponding to deformation vibrations of the dioxolane ring indicates that dihydrated glyoxal oligomers are formed in glyoxal solutions with concentrations of 1 M and higher. Under typical ambient temperature and humidity conditions, concentrated glyoxal solution droplets undergo evaporation with incomplete water loss. Our results suggest that formation of crystalline glyoxal trimer dihydrate from concentrated solutions droplets is hindered by the high viscosity of the amorphous trimer and requires dry conditions that could rarely be achieved in the atmosphere. Hence, in the atmosphere particles containing these organic compounds may be present in an amorphous state under a broad range of conditions.