Probing aerosols by photoelectric charging

Abstract

Particles suspended in a gas may emit photoelectrons upon irradiation with ultraviolet light. It is shown that photoemission from small particles involves material and surface dependent physical processes that yield new information, especially on ultrafine particles not accessible to the well-known diffusion charging. An apparatus is presented for the measurement of the electric mobility and the charge generated on particles in the atmosphere using a monochromatic low-pressure Hg arc. Particles generated by combustion of organic material, e.g., auto exhaust, are charged with high efficiency. This offers a new way to detect and/or remove such particles from the air. In outside air the concentration of photoelectrically active particles has a diurnal cycle which also depends on the meteorological conditions. Surprisingly, highly mobile particles are detectable even during rainfall.