A major source of uncertainty in predicting climate change is due to our incomplete understanding of how various types of mixed-phase particles in the atmosphere interact with short-wave solar radiation and long-wave radiation from Earth’s surface. The extent that mixed-phase particles scatter light and cool the atmosphere or absorb radiation and warm the atmosphere depends on the internal structure and chemical composition of particles as well as their overall size and shape. Since particle composition significantly affects optical properties, it is necessary to investigate microscopically the three-dimensional chemical structure of individual particles. Another recent environmental concern is the identity and amount of microplastics in ambient air. As with atmospheric particles affecting climate, microscopy of individual microplastic particles is necessary to quantify the extent that airborne microplastics are airborne pollutants.

Focused ion-beam scanning electron microscopy (FIB-SEM) is a principal technique that we use to probe inside atmospheric particles. The technique is a type of tomography that involves high-precision ion milling of the particle along with SEM imaging and energy-dispersive x-ray microanalysis (EDX) to produce a sequence of SEM images and compositional maps of the particle’s interior. The serial images and maps are then used to create a 3-D rendering of the particle. The 3-D representation may then be used as input to radiative transfer models to calculate, for example, the amount and angular distribution of light scattered by the particle and the ratio of scattering to total extinction (i.e., the single-scattering albedo).

Other microbeam techniques that we use to analyze climate-relevant and microplastic particles include micro-Raman spectroscopy for polymeric compounds, computer-controlled SEM to analyze particle populations, electron backscatter diffraction to determine the crystalline phases, variable-pressure SEM to investigate deliquescent particles, and high-resolution scanning transmission electron microscopy to analyze, at the nanometer scale and below, the chemical structure of ultrafine atmospheric particles.

key words

Atmospheric aerosols; Microplastics; Climate change; Electron microscopy; X-ray microanalysis; Raman spectroscopy; Microbeam analysis;

Citizenship:  Open to U.S. citizens

Level:  Open to Postdoctoral applicants