Abstract View
Using Model Particle Systems to Constrain Atmospheric Particle "Glassiness" and Mixing Limitations
LUKE HABIB, Neil Donahue, Carnegie Mellon University
Abstract Number: 257
Working Group: Wildfire Aerosols
Abstract
Atmospheric aerosols have highly uncertain and poorly understood effects on climate change and human health. That uncertainty is in part due to uncertainty surrounding the mixing state of aerosol populations, which is commonly assumed to be well internally mixed. If atmospheric aerosols are not internal mixtures, it could change how we understand their health and climate effects. When distinct aerosol populations come together, mixing should happen on a time scale of a few hours to support the internal mixing assumption. Gas-phase exchange between aerosol populations via evaporation and condensation of semi-volatile organics (“Marcolli mixing”) can be a major mechanism of mixing between accumulation-mode particles with slow coagulation. Viscous, semi-solid, or “glassy” particles may impede this by posing diffusion limitations to evaporation and/or condensation. Here we describe experiments on carefully prepared particle populations representing “glassy” aged organic particles (various non-volatile sugars as well as laboratory generated SOA with ammonium sulfate seeds) and fresh biomass burning particles (erythritol with black carbon seeds) to develop a model phase space for organic aerosol systems and better understand when particle “glassiness” impedes mixing. We quantify the mixing state of these particle populations using an Aerosol Mass Spectrometer (AMS) in the Event Trigger (ET) and Soot Particle (SP) modes simultaneously. The ET mode of the AMS records single-particle mass spectral data by “triggering” data acquisition when desired mass-to-charge ratios are detected and the SP mode enables refractory black carbon particles to be characterized. Our results suggest that the non-volatile sugar particles have no diffusive limitations to mixing at the conditions tested. Preliminary results suggest that laboratory generated SOA particles have diffusive limitations to mixing at certain conditions. Our hypothesis is that these limitations are alleviated at some relative humidity threshold, which increases with decreasing ambient temperatures.