Metrological Performances of a Diffusion Charger Particle Counter for Personal Monitoring

Airborne particles have been shown to be associated with a wide range of adverse health effects, and have thus attracted an increasing amount of attention by medical researchers. However, accurate evaluations of the related exposure-dose-response relationships are highly dependent on the ability to track people's actual exposure to airborne particles. This is quite a complex task, particularly in relation to submicrometer and ultrafine particles, which can vary quite significantly in terms of particle surface area and number concentration. It is thus necessary to develop suitable monitors that can be worn in order to measure personal exposure to these particles. This paper presents an evaluation of the metrological performance of six diffusion charger sensors, namely NanoTracer (Philips Aerasense) monitors, when measuring particle number and surface area concentrations, as well as particle number distribution mean, when compared to reference instruments. Tests in the laboratory (by generating monodisperse and polydisperse aerosols) and in the field (using natural ambient particles) were designed to evaluate the responses of these devices under both steady-state and dynamics conditions. The results show that the NanoTracers performed well when measuring steady state aerosols, although they strongly underestimated the actual concentrations during dynamic response testing. The field experiments also showed that, when the majority of the particles were smaller than 20 nm, which occurs during particle formation events in the atmosphere, the NanoTracers underestimated the number concentration quite significantly. Overall, even though NanoTracers can be used for personal monitoring of exposure to ultrafine particles, they have some limitations which need to be considered in order to obtain meaningful results.