10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Evaluation of Relative Humidity Impacts on Biomass Burning Aerosol Particle Viscosity and Volatility using a Tandem Differential Mobility Analyzer
CHRISTOPHER OXFORD, Rajan K. Chakrabarty, Brent Williams, Washington University in St. Louis
Abstract Number: 1497 Working Group: Carbonaceous Aerosol
Abstract High viscosity of the condensed phase has been predicted to inhibit diffusion of organic species in aerosol particles1. The characteristic time for diffusion of particle-phase organic species could vary by orders of magnitude depending on the particle’s viscosity. High viscosities would prevent evaporation of organic species, while lower viscosity would have little or no discernable impact2. Since vapor pressure and enthalpy measurements often use kinetic methods to characterize the aerosol, results from those measurements could be biased by particle-phase viscosity effects.
The inclusion of water in the condensed phase will reduce the particle viscosity and has been shown to reduce the characteristic time for diffusion3. The presence of inorganics in aerosols increases the ability of the particles to uptake water in an elevated relative humidity (90%) environment. Therefore, aerosol sources containing both inorganics and organics provide an ideal system for assessing the influence of relative humidity on primary particle phase volatility.
Flaming combustion of herbaceous plants often emits inorganic species, but the inorganics do not emit during low temperature (200 C) smoldering combustion. By varying the combustion phase (flaming vs smoldering vs mixed), we can alter the inorganic/organic content, and therefore the hygroscopicity of the aerosol. Water vapor can then be introduced to the aerosol to assess the impact of viscosity on primary emissions.
We emitted primary aerosol from the combustion of herbaceous plants and used a Tandem Differential Mobility Analyzer coupled with a Centrifugal Particle Mass Analyzer to measure the vapor pressure and enthalpy of the primary aerosol. By altering the relative humidity of the aerosol stream, we determine the impact of water on the apparent volatility of the emitted aerosol.
[1] Koop, T., Bookhold, J., Shiraiwa, M. & Poschl, U. Glass transition and phase state of organic compounds: dependency on molecular properties and implications for secondary organic aerosols in the atmosphere. Phys Chem Chem Phys 13, 19238-19255, doi:10.1039/c1cp22617g (2011). [2] Shiraiwa, M. & Seinfeld, J. H. Equilibration timescale of atmospheric secondary organic aerosol partitioning. Geophys Res Lett 39, doi:Artn L24801 doi: 10.1029/2012gl054008 (2012). [3] Shiraiwa, M., Ammann, M., Koop, T. & Poschl, U. Gas uptake and chemical aging of semisolid organic aerosol particles. P Natl Acad Sci USA 108, 11003-11008, doi:10.1073/pnas.1103045108 (2011).