Measure particles below the optical range (<300 nm) as well as in the ultrafine region (<100 nm).

Lead Research Organisation: University of Cambridge
Department Name: Engineering

Abstract

There is great interest in the measurement of particulate levels in the environment. Current legislation mandates measurements of PM2.5 and PM10 but there is a drive to measure particles below the optical range (<300 nm) as well as in the ultrafine region (<100 nm).
In previous projects we have developed compact sensor techniques for measuring the second moment of the particle distribution (nd2) using UV photoionization and electrometry [1,2]; a new technique using bipolar charging in an inexpensive sensor has been shown to offer an absolute measurement of the first moment (nd) [3,4]. These techniques have been favourably compared to other sensors, including corona-based sensors such as Partector, which use corona discharge, and result in measurements of nd1.1[5].
These two techniques are currently being developed as practical sensors for ultrafines, yet much remains to be done to understand the practical limits and advantages of the two techniques relative to existing systems such as aethalometers. In the case of the photoionization method, there a number of issues which need to be further explored and solutions developed:
- Sensitivity to relative humidity (signal loss)
- Materials sensitivity not fully understood: insensitive to salts, probably sensitive to presence of PAHs
- Understand the correlation between the signal from the photoionization method with other devices (aethalometers, corona ionization) in controlled and uncontrolled field applications.
The (nd) sensor based on low-cost radiation ionization has been demonstrated over a wide range of diameters (40-1000 nm), but the device has yet to be tested with a variety of materials and background gases. A number of topics need to be further investigated, including:
- Comparison of the range of values for mobility ratio of ions (Z+/Z-) relative to previous studies
- Determination of the desirable minimum range of ion concentration and residence time (nit) per unit particle concentration compatible with equilibrium conditions required for the operation of the sensor
- Sensitivity to operating conditions (humidity, background)
- Correlation of signal between the signal from the (nd) method with other devices (aethalometers, corona ionization) in controlled and uncontrolled field applications.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/S023593/1 01/04/2019 30/09/2027
2440023 Studentship EP/S023593/1 01/10/2020 30/09/2024 Joshua Hassim