AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Solidification of Organic Aerosol Particles Caused by Glyoxal +OH Radical Reactions
ALYSSA ANDRETTA, David De Haan, University of San Diego
Abstract Number: 444 Working Group: Aerosol Chemistry
Abstract The recent discovery that atmospheric organic aerosol particles are often semi-solid, rather than liquid, encourages the rethinking of how organic aerosol processes work. In bulk-phase aqueous studies performed at high concentrations, glyoxal + OH radical reactions have been reported as a source of oligomers. To determine whether this oligomer formation process can lead to rapid solidification of aerosol particles, a solution of glyoxal and hydrogen peroxide was mixed, photolyzed with a UV lamp at 366 nm, and aerosolized into a Teflon chamber via diffusion dryers. The resulting particles were exposed to increasing levels of humidity (from 25% to 50% RH) while their size distribution was measured. Control experiments were performed without UV light exposure or without HOOH. Unphotolyzed glyoxal + HOOH solutions yielded the largest aerosol particles, perhaps because they remained liquid. Photolyzed (glyoxal + ŸOH radicals) solutions generated significantly smaller aerosol particles in the chamber. Oxidation of glyoxal by OH radicals may have led to fragmentation reactions and loss of CO2 to the gas phase. Alternatively, oligomers produced by glyoxal + ŸOH radical reactions may have solidified the droplet surface during drying, producing hollow, semi-solid aerosol which later “popped” to produce smaller fragments, as previously observed in Raman microscopy experiments. In humidification experiments, aerosol generated from solutions without ŸOH radicals increased the most in size, while solutions with ŸOH radicals increased the least. This suggests that oligomers produced by the glyoxal + ŸOH radical reaction are comparatively hydrophobic.