Basic concepts and development of dry deposition modelling

Abstract EN

Dry deposition is the primary mechanism by which suspended particles are transported from gas onto surfaces.

Prediction of this transport rate represented by the dry deposition velocity (Vd) is needed in a vast range of applications, such as atmospheric climate and air quality models, industrial processes, nanomaterials, clean rooms, building engineering, particle losses inside sampling lines, health effect of atmospheric particles and pharmaceutics.

The particle transport rate towards the surface depends on many factors: above-surface air flow and fluid characteristics, physical characteristics of the particles and surface properties.

Although dry deposition models have been improved significantly, they still need to be further developed to improve the model accuracy and include weak mechanisms of particle transport.

In general, a dry deposition model incorporates Fickian diffusion (Brownian and Eddy) and gravitational settling.

Turbophoresis was introduced to compensate for the enhancement in Vd as a result of inhomogeneous turbulent mixing.

In real-life conditions, electrophoresis and thermophoresis are not strong enough mechanisms to be included in model calculations, but for some applications (such as air purifiers), these transport mechanisms are very important to be considered in model formulation.

Magnetophoresis, which is a very weak mechanism in real-life conditions, can be enhanced for certain industrial applications.

In general, deposition surfaces are rarely smooth and researchers have put great efforts to describe surface roughness in dry deposition models.

After all, a unified dry deposition formulation is needed to be developed/ improved in the future to make dry deposition prediction and calculations easier and more accurate.

In this paper, we present the basic concepts that have been developed and implemented in dry deposition models and illustrate the effect of different processes on the transport rate of suspended particles in the fluids towards surfaces.

As a benchmark for the accuracy of the current dry deposition modelling, we present a comparison between model calculations and experimental data-bases found in the literature.