Duration of tangent-linear regime in sectional multi-component aerosol dynamics

Abstract

In this article, a tangent-linear multi-component aerosol dynamical box model was studied. In particular, the length of time over which the tangent-linear dynamics dominate the total evolution of a particle number concentration perturbation is determined. In the experiments, three non-linear model initial number concentration distributions, perturbation distributions, and ambient vapour concentrations are used. Results indicate, based on analysis of the evolution of number distribution perturbation, that in pure nucleation events the tangent-linear regime persists for about 1.5 h, and can last for several hours in cases of weak nucleation. Analysis of the perturbation evolution with emphasis on particle surface area or volume indicates that the dynamics is tangent-linear over a much longer period. In conclusion, high ambient sulphuric acid vapour concentration maintains a large number concentration of small particles (below about 10 nm) through nucleation. These particles are the prime source of non-linearity limiting the length of the tangent-linear regime in a box model context. The results have relevance, but are, however, not directly applicable, for instance, in three-dimensional chemical transport and air-quality modelling aiming to incorporate data assimilation techniques, such as four-dimensional variational data assimilation.