AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Effects of Aerosol-Phase and Bulk Aqueous-Phase Browning in Aldehyde Reactions with SO2
BENJAMIN JOYCE, David De Haan, University of San Diego
Abstract Number: 536 Working Group: Effects of NOx and SO2 on BVOC Oxidation and Organic Aerosol Formation
Abstract Climate can be affected by the aqueous-phase formation of aerosol brown carbon from aldehyde reactions with SO2, due to the resulting increase in sunlight absorbed by aerosol particles. Previous studies have found that brown carbon formation occurs in the dark due to quinone formation, but this study focuses on the effect of UV exposure on brown carbon formation in bulk aqueous solution and aerosol phases. Aqueous aldehyde + SO2 bulk reaction mixtures studied at pH ~ 5.5 and concentrations of 0.25 M were analyzed via ultraviolet-visible spectroscopy (UV- Vis) to characterize the production of brown carbon products (indicated by increased absorbance in the range ~ 350-450 nm). These same aqueous solutions were either placed in vials and exposed in varying UV environments for 10 h to allow production of brown carbon or used to generate aerosol. These aerosol particles were dried in silica gel diffusion driers, and collected on Teflon membrane filters for 2 - 4 h. The filters were ultrasonically extracted in Milli-Q water, and the extract was also analyzed via UV-Vis to quantify the formation of brown carbon products. The UV environments consisted of exposing samples to direct sunlight, direct UV light (366 nm), and dark control environments. The spectroscopy data was compared on a per mass basis using mass absorption coefficients. Bulk aqueous glyoxal + SO2 solutions browned under all conditions, with the most browning in dark control conditions and the least in direct sunlight. Glyoxal + SO2 aerosol browned almost twice as fast as the corresponding bulk aqueous solution. Aqueous and aerosol methylglyoxal + SO2 solutions did not reliably form brown products in any UV environment.