AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Aerosol Particle Browning and Production of Semivolatile, Light-Absorbing Species upon Exposure to Gas-Phase Methylglyoxal or Methylamine
DAVID DE HAAN, Natalie Jimenez, Alexia De Loera, Paola Formenti, Mathieu Cazaunau, Aline Gratien, Jean-François Doussin, University of San Diego
Abstract Number: 348 Working Group: Aerosol Chemistry
Abstract Cloud processing causes important changes in aerosol particles. Wet scavenging of water-soluble gases, aqueous-phase oxidation, and other reactions can increase the amount of organic material and cause the particles to absorb light. Oligomer formation during droplet drying can produce semi-solid organic phases that slow the kinetics of subsequent chemical and physical processes within the particle. We report on aerosol chamber experiments with common atmospheric aldehydes (e.g. methylglyoxal), amines (methylamine, glycine), and ammonium salts. Gas-phase species are monitored by high-resolution PTR-MS, while particles and droplets are monitored for size (SMPS, WELAS), optical parameters (CAPS-PMssa, PILS / UV-vis), physical characteristics (aerosol bounce) and offline speciation (high-resolution LC-ESI-MS of aqueous filter extracts). CAPS data indicates that particle browning upon exposure to methylglyoxal or methylamine gas can occur on a timescale of less than 1 min, and is sensitive to chamber RH. However, SMPS data shows that dried particles exhibit only negligible increases in mass during browning. Furthermore, cloud events in this system trigger post-cloud uptake of volatile imine products and the production of a 2nd-generation semivolatile species that absorbs light at 450 nm. Brown carbon production rates measured in aerosol particles exceed those measured in bulk-phase experiments by at least four orders of magnitude, well in excess of any concentration effects. This suggests that surface reaction processes are dominant in the aqueous-phase atmospheric chemistry of methylglyoxal.