Diffusion Charging-Based Aerosol Instrumentation: Design, Response Characterisation and Performance

Abstract

The growing concern for the air quality in urban areas and the subsequent development of measurement networks has increased the need for lightweight and cost-effective air quality instrumentation. In urban areas, traffic-related emissions are one of the major contributors to the worsened air quality, which in turn has led to the stringed emission regulations set for vehicles. These regulations necessitate both on-board monitoring of the operation of the exhaust after-treatment devices and measurement of the real-word driving emissions with portable emission measurement systems. Both of these aspects increase the demand for sensor-type instrumentation for emission measurement.<br/><br/>This thesis focusses on the development of diffusion charging–based aerosol instrumentation towards more compact and sensor-type instruments. The work was started by developing an add-on module for the electrical low-pressure impactor. This extended the instrument measurement capabilities by enabling the measurement of the effective density of particles in real-time. Focussing more on the sensor-type instrumentation, three different sensors were presented for measuring particle emission directly from the exhaust line: Two of them targeting the engine laboratory work or for the portable emission measurement and one designed for on-board diagnostics. The instrument developed for the on-board emission measurement provided a very good temporal performance owing to the miniaturisation of the instrument design. Lastly, a new sensor design approach was presented in which the flow rate dependence of the instruments response is minimised. This, together with the minimised pressure drop in the design, helps in lowering the instrument cost by promoting the use of a low-cost fan for generating the sample flow.<br/><br/>Instrument response characterisation and response modelling made a central part of the study. Results from the characterisation measurements were presented for all instruments, and comprehensive response models were built for the sensor-type instruments. Depending on the instrument, both simplified approximations and theoretical responses of the instrument components were used as the starting point for the response models. Additionally, the instrument performance was demonstrated in practical measurements related to the application of each instrument. The obtained response models provide necessary information for the instrument performance evaluation and the measurement data processing.