On the Relationship Between Aerosol Dynamics and the Rate of Gas-to-Particle Conversion

A theoretical and experimental study of the dynamic behavior of secondary aerosols generated by homogeneous gas phase reactions is presented. The relationship between the rate at which new aerosol is formed by chemical reaction and the development of the aerosol is emphasized. The effect of an initial aerosol, present at the start of gas-to-particle conversion, on aerosol dynamics is also investigated. Aerosol dynamics in such systems are typically separated into two stages. During the early stage, new particles are often formed by homogeneous nucleation. Particle concentrations rise to a maximum value after timescales of 10-60 minutes, then decrease continually as the coagulation rate exceeds the rate at which new particles are formed. A new theory which predicts the rate at which new particles of a given size are formed during the early stages of aerosol growth is presented. This rate is shown to be a known function of a single parameter which depends on the rate at which condensable molecules are produced and on the amount of preexisting aerosol surface area per volume of gas. This parameter can be calculated from experimental data.