Abstract View
Using Model Particle Systems to Constrain Atmospheric Particle “Glassiness” and Mixing Limitations
LUKE HABIB, Neil Donahue, Carnegie Mellon University
Abstract Number: 119
Working Group: Aerosols, Clouds and Climate
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, especially for atmospheric models. If atmospheric aerosol particles are not internal mixtures, it could be much more difficult to understand their health and climate effects. When distinct aerosol populations come in contact with each other, mixing should happen on a time scale of a few hours in order to support the internal mixing assumption. For semi-volatile organics, gas-phase exchange between aerosol populations via condensation and evaporation (“Marcolli mixing”) can be a major source of mixing between accumulation-mode particles with slow coagulation. However, the existence of viscous, semi-solid, or “glassy” particles may impede this by posing potential diffusion limitations to Marcolli mixing. Here we describe experiments on carefully prepared particle populations representing “glassy” aged organic particles (glucose particles with ammonium sulfate seeds) and fresh biomass burning organic aerosol particles (erythritol particles with black carbon seeds) to develop a model phase space for organic aerosol systems and better understand when particle “glassiness” impedes gas-phase exchange of semi-volatile organics. The mixing state of these particle populations is quantified 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 based on “triggering” data acquisition at desired mass-to-charge ratios and the SP mode allows for refractory black carbon particles to be characterized. Preliminary results and previous studies suggest that at some relative humidity threshold, glassy particles will plasticize and diffusive mixing limitations will break down; we expect the relative humidity of the glass transition to increase with decreasing temperature.