Custom Particles for Aerosol Field Calibration

A breakout meeting of ARM/ASR users determined that some of the greatest needs in the subject of aerosol measurement has to do with unsolved challenges for aerosol standards. It is known that calibrations drift after they have been performed in the lab. Sources of particles of known composition and mass are fundamental needs for field calibrations. More specifically it is important to be able to generate particles of known scattering and absorption properties and known shape factor. The Phase I will be to show that it is feasible to produce monodisperse particles with known composition and relevant shapes through lithography or other processes, and to test the produced particles on a laboratory instrument. It may also be useful to pre-sort particles that are currently commercially available as a way of reducing the uncertainty in their properties. During Phase II, the most promising type or two) of particles from Phase I will be selected and the work would focus on increasing throughput and uniformity. During Phase I, several candidate particles will be chosen for production, some with complex, but reproducible shapes and some with better characterized scattering and absorption properties. The particles will be characterized with scanning electron microscopy, transmission electron microscopy, optical microscopy and optical spectroscopy. Next, a method to disperse the particles at a known concentration will be implemented. Finally, the particles will be used to calibrate a cavity ring-down spectrometer, and the resulting uncertainty will be compared to the uncertainties resulting from standard calibration procedures. Besides producing kits to sell to atmospheric scientists to enable more accurate field calibrations, the processes developed for this program can also be applied to the production of nano- and microparticles to be used in medicine.