Date: Wednesday, September 5, 2012
Location: PHYS 401
Optical, microphysical and compositional properties of volcanic ash, soil dust, urban pollution and other aerosols.
The microphysical properties of aerosols are of fundamental importance in the estimation and prediction of their direct and indirect forcing effects on the balance of energy of the Earth. One of the main parameters missing in current atmospheric models is the complex refractive index of aerosol particles from the ultraviolet (UV) to the short-wave infrared (SWIR) wavelength. The main objective of this project is to perform a detailed characterization of important optical and microphysical properties of aerosol particles, and create a database for these commonly missing parameters. This research proposes to investigate the geometrical size distribution, shape, material density, and imaginary part of the refractive index of different types of aerosols from UV to SWIR wavelengths. The proposed methodology includes in situ measurements using the LACO-UMBC Reflec-Nephelometer, and aerosol in situ filter collection using the LACO Aerosol Sampling Stations. Also, materials can be collected directly from the ground (like deposited volcanic ash, or dust) and brought to our laboratory for posterior re-suspension. Our experimental setup allows us to separate particles into PM10, PM2.5, or PM1.0. Particles collected on filters are analyzed by different techniques, such as Scanning Electron Microscopy (SEM) for determination of size distribution, reflectance measurements for determination of the optical absorption properties as a function of the wavelength, and Proton Induced X-ray Emission (PIXE) or X-Ray fluorescence for elemental composition. Finally, the spectral imaginary part of refractive index (from 300 to 2500nm) is derived numerically from the measurements of mass absorption coefficient, size distribution and geometrical shape of the particles, and the density of the material. The selected samples for this study include materials collected at vicinity of volcanic eruptions at Eyjafjallajökull (Iceland), Puyehue (Chile), Mont Saint Helens and Fuego Volcano (USA), dust from central Sahara at Birmoghrein (Mauritania) and Bordj Mokhtar (Algeria), and urban pollution with distinct organic and black carbon components.