AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Formation of Semi-solid, Oligomerized Aqueous SOA: Cloud and Aerosol Lab Simulations
LELIA HAWKINS, Amanda Lemire, Katherine Muller, David De Haan, Molly J. Baril, Alec Rynaski, Nahzaneen Sedehi, Harvey Mudd College
Abstract Number: 713 Working Group: Aerosols, Clouds, and Climate
Abstract Glyoxal and methylglyoxal form high molecular weight (HMW), N-containing compounds during simulated cloud processing with small amines, amino acids, and ammonium sulfate (AS); the measured residual particles are semi-solid and may require equilibration with humid air beyond the traditional 1-2 s residence time in hygroscopicity tandem differential mobility analysis (HTDMA). Using a novel HTDMA system that allows varied residence time in the humidification chamber, the hygroscopic growth (HG) of each of the resulting products of simulated cloud processing was measured. Gradual deliquescence was observed beginning at 40% RH. Using longer humidification times (20 min vs 3.4 s) produced an increase in growth factors for the glyoxal-methylamine (19% by vol) and methylglyoxal-methylamine (8% by vol) systems, indicating that the 3.4 s residence time was insufficient to achieve equilibrium. Semi-solid products showed a measurable impact on the deliquescence relative humidity (DRH) and growth of AS aerosol, with up to 7% reduction in DRH and up to 10% reduction in growth factor at 80% relative humidity. Droplet evaporation experiments showed that the mixed glyoxal-AS particles, but not methylglyoxal-AS, require at least 30 min of drying to achieve equilibrium, due to the reduced diffusivity of water in the semi-solid particles. To compliment the HTDMA measurements, atomic force microscopy was used to probe the viscosity (liquid-like, glassy, rubbery, crystalline) of the simulated particles. Results show that for some SOA mimics, particles are more like rubber than organic liquid or crystalline solids.