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

An experimental apparatus for measuring the kinetics of the reactive uptake 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 the position at which the gas is added to the aerosol flow. The gas phase species concentration is measured by chemical ionization mass spectrometry. Sulfuric acid aerosol is generated by the gas phase reaction between SO3 and H2O. The aerosol have lognormal radius distributions with 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) particles cm(-3) in the reactor) is measured in a separate apparatus by monitoring the extinction of visible light by the growing particles following a rapid expansion at high relative humidity. The size distribution of the aerosol in the reactor is extracted from measurements of the UV transmission between 200 and 400 nm by using Mie theory. Kinetic results for the reaction of N2O5 with 70 wt % sulfuric acid aerosol at room temperature are presented.