Abstract Number: 623 Working Group: Instrumentation and Methods
Abstract Organic aerosols exhibit variability in their phase state and viscosity based on their material composition and the environmental conditions (like temperature and relative humidity). Viscosity of the organic aerosols influences particle growth rate, diffusivity, chemical reactivity, mixing state, and impacts the long-range transport of pollutants. Therefore, investigating the evolution of phase state/viscosity of organic aerosol or organic material with changing environmental factors is critically important. Currently available viscosity measurement techniques cater particle sizes greater than 20μm, whereas atmospheric aerosols span submicron size ranges, which emphasizes the need of developing new apparatus for characterizing material properties of individual organic particles of atmospherically relevant size range while controlling the temperature and relative humidity.
In this study we present a novel technique combining Environmental Scanning Electron Microscopy (ESEM) with custom made environmental cell to allow tilted viewing of the sample while controlling the environmental conditions (relative humidity and temperature). Imaging particles in tilted view enables distinguishing particles based on their deformability when impacted on substrate during sample collection. Deformability of a particle is directly linked to the viscosity or phase state of its constituting material. Tilted imaging and ESEM together enabled us to investigate viscosity/phase state of various organic aerosols at given set of environmental conditions. Here, we discuss the principle and design of the novel set-up, present the results from the water uptake experiments, and report the phase transformation and hygroscopic growth factors of standard atmospherically relevant organics and ambient organic aerosol mixtures as a function of relative humidity and temperature. In next phase of development, we plan to introduce physical poking of the individual particles with micro-manipulator to obtain an estimate of their viscosities/phase states via poke-flow technique in ESEM.