MEASUREMENT OF THE KINETICS OF REACTIVE UPTAKE BY SUBMICRON SULFURIC-ACID PARTICLES

An experimental apparatus for measuring the kinetics of the reactive u ptake of gas phase species by sulfuric acid aerosol is described. The reactive uptake is studied by monitoring the concentration of the gas phase species at the exit of a laminar flow reactor as a function of t he position at which the gas is added to the aerosol flow. The gas pha se species concentration is measured by chemical ionization mass spect rometry. Sulfuric acid aerosol is generated by the gas phase reaction between SO3 and H2O. The aerosol have lognormal radius distributions w ith peak radii in the range 0.05-0.15 mu m with a radial dispersion of about +/- 30%. The particle number density (5 x 10(4)-1 x 10(6) parti cles cm(-3) in the reactor) is measured in a separate apparatus by mon itoring the extinction of visible light by the growing particles follo wing a rapid expansion at high relative humidity. The size distributio n of the aerosol in the reactor is extracted from measurements of the UV transmission between 200 and 400 nm by using Mie theory. Kinetic re sults for the reaction of N2O5 with 70 wt % sulfuric acid aerosol at r oom temperature are presented.