Measuring Aerosol Active Surface Area by Direct Ultraviolet Photoionization and Charge Capture in Continuous Flow
R.T. Nishida1, Adam Boies1, Tyler Johnson1, Nene Yamasaki1, John Saffell2, Simone Hochgreb1
1Department of Engineering, University of Cambridge, Cambridge, CB2 1PZ, UK
2Alphasense Ltd, 300 Avenue W, Great Notley, Braintree, CM77 7AA, UK
Direct ultraviolet (UV) photoemission yields electrical current measurements proportional to aerosol active surface area which is of interest for emissions, environmental or exposure monitoring. However, the fundamental mechanisms of photoemission must be understood to accurately interpret measurements in the field. In this work, photoemission theory is evaluated by analysing photoelectric current measurements for a range of aerosol particle types, sizes, concentrations, and morphologies. Sintered silver spheres and aggregates are classified with an aerodynamic aerosol classifier (AAC) allowing a direct comparison of aerosols of the same material and electrical mobility, but with different morphologies. Photoemission measurements from raw and thermo-denuded flame soot confirm surface-dependent effects on photoemission yield. A 3D computational model of particle charging and transport is used to demonstrate the effect of particle polydispersity on integrated electrical current. Experimental and modelling results show good agreement for a range of conditions, providing confidence in the theory and modelling techniques used.