Impaction model for the aspiration efficiencies of aerosol samplers at large angles with respect to the wind

Abstract

This paper starts off by recognising that the development of a full theoretical description of the aspiration efficiencies of samplers like those used in real-life situations is still some way off. As an interim contribution to solving the problem, it describes how the simple impaction model approach, which has previously been widely applied to thin-walled sampling probes and to blunt samplers under very idealized conditions, can be extended semi-empirically to describe the performances of contrasting types of sampler—thin-walled probes and the human head—oriented at 90° and 180° to the wind, respectively. Physically-based models for aspiration efficiency at these orientations are suggested and their coefficients found by non-linear regression against the limited amount of relevant data available in the literature. Agreement between such models and the experimental data is found to be quite good. Such models have the potential to provide useful insight into the performances of practical sampling devices. Furthermore they can provide valuable guidelines for the development of more rigorous approaches to blunt sampler theory.