Development and Integration of Ultrafine Particle Charging Sensors

Theme: Measurement Techniques

Start date: Cohort 2: 2020

Supervisors: Prof. Simone Hochgreb (Cambridge)

Sub-micron particulates are important pollutants, but difficult to measure with inexpensive methods. This project will use and further develop two low-cost sensors developed by the group to measure total particle area (nd2) or total particle length (nd) and thus diameter (d) in the atmosphere.


Ultrafine aerosol particles, those with diameters less than100 nm, are known to be a major risk to human health due to their high number concentrations and ability to penetrate deep into the human lung.  Evidence of the effects of ultrafines from local anthropogenic sources is limited owing to the sparse availability of appropriate sensors allowing for monitoring of particles in this size range.  Current methods for ultrafine detection often rely on either expensive, complex, large bench-top systems or low-cost sensors which only provide accurate measurements for controlled sources. Low-cost charging devices, such as those utilising bipolar or photoelectric charging, offer the potential for cost effective, deployable sensors for ultrafines. Further investigation is required to understand the operating principles, practical limits and advantages of these techniques. The individual response from charging devices, as well as other low-cost instrumentation, provides a measure of average size and concentration (moment measurements), not a fully resolved particle size distribution (PSD). However, combinations of low-cost sensors can be used to; reckon individual measures of number concentration, average particle diameter; attribute the chemical fingerprint and even determine the size distribution of an aerosol. Therefore, networks of low-cost, portable sensors could be used in a wide array of applications, including vehicle emission monitoring, epidemiological studies, workplace exposure and policy informing in urban areas, to provide better characterisation of an aerosol than could be obtained by a single sensor. In order to integrate different measurements the response of each individual sensors needs to be fully understood and characterised. A research plan is proposed highlighting the use of a combination of computational fluid dynamics modelling, laboratory experimentation and ambient measurements to investigate the effects of: aerosol surface chemistry, composition, morphology; as well as charger design for photoelectric and bipolar charging sensors.  A brief discussion on the potential future application to policy along with responsible innovation is also provided.