Development of an ultraviolet constant angle Mie scattering detector toward the determination of aerosol growth kinetics in the transition and free molecular regime

Abstract

The measurement of aerosol growth kinetics at ever smaller sizes toward the transition and free molecular regime is of interest to provide for validation of theoretical predictions. Such measurements remain challenging to accomplish, particularly those occurring in the kinetic regime. Toward this goal, an instrument based on the ultraviolet constant angle Mie scattering (UV-CAMS) method was developed. The instrument utilizes adiabatic expansion to cause supersaturation and drive aerosol growth. Aerosol particles growing by water condensation are illuminated with a pulsed UV laser at 337 nm wavelength and a reference laser with red light (wavelength of 632 nm). The scattered light fluxes at 30° are measured simultaneously and are then compared with size resolved Mie scattering calculations providing aerosol growth measurements. The growth curves obtained from UV match those from the red laser. These measurements allow us to see the first Mie peak for UV scattering for particles in the 500 nm range. This is an almost two-fold resolution increase compared to the smallest particles that can be seen via red laser scattering in similar conditions (first Mie peak above 900 nm).