An Initial Assessment of the Viscosity and Phase State of Wildfire Smoke Particles in the Stratosphere
Allan K. Bertram, MEI FEI ZENG, Andreas Zuend, Daniel Murphy, Gregory Schill, University of British Columbia
Abstract Number: 217
Working Group: Aerosols, Clouds and Climate
Abstract
Large wildfires periodically eject massive amounts of biomass burning organic aerosol (BBOA) into the stratosphere, where it can linger for many months and catalyze ozone-destroying reactions. To predict this multiphase chemistry, information is needed on the viscosity and phase state of BBOA. In the following, we used laboratory data and a thermodynamic model to assess the viscosity and phase state of BBOA in the stratosphere. Results suggest that the unaged BBOA and BBOA aged 1.5 days by hydroxyl radicals are in a glassy state for a wide range of temperatures in the stratosphere (approximately 200-275 K). After long-term aging (weeks to months) and H2SO4 uptake (25 wt % H2SO4), the particles may still be in a glassy state or more viscous than tar pitch (108 Pa s) between approximately 205-245 K in the stratosphere. These high viscosities could shut off bulk reactions within BBOA particles, and the glassy state could nucleate crystalline polar stratospheric clouds, which can amplify stratospheric ozone depletion. If the H2SO4 content reaches 50 %, BBOA likely do not form a glassy state for the full range of temperatures in the stratosphere. However, the viscosities could still reach as high as 106-1010 Pa s for some conditions in the stratosphere, which could influence multiphase reaction rates within BBOA. Additional studies are needed to confirm the predictions presented here.