Portable and Non-Intrusive Sensors for Monitoring Air Pollution
University of Cambridge
Doctor of Philosophy (PhD)
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Oluwasanya, P. (2019). Portable and Non-Intrusive Sensors for Monitoring Air Pollution (Doctoral thesis). https://doi.org/10.17863/CAM.54901
Air pollution is a global problem. Particulate Matter (PM) of aerodynamic diameter smaller than 2.5 μm (known as PM₂.₅) and NO₂ are important classes of pollutants because of their size and emission sources and potential effects of exposure beyond 25 μm/m³ and 40 μm/m³ annual mean respectively. This thesis presents work that has been done to develop new and miniaturized/non intrusive (<1 cm³ in volume) sensors for monitoring both classes of pollutants. A review of the current landscape of both sensor types was carried out and the challenges identified. For PM, it is the price (>$300), size (smallest ones are several tens of cm³ in volume) and the accuracy (±10%) of the sensors that motivated the design, simulation and subsequent fabrication of the miniaturized device. It is shown that the capacitive-based sensor is easily miniaturizable and has sensitivity to single particles flowing at a distance of up to 18 μm above the electrode surface. This new sensor concept and its simulated multiphysics model is unique because it uses thermophoresis to separate particles of PM₂.₅ and PM₁₀ from a single airflow. For the NO₂ sensors, the availability of selective sensors that function in humid environments is a major need. Further, both sensor types need to be robust against interferent species and environmental variations. In this thesis, I present chemiresistors based on graphene/carboxymethyl cellulose (CMC) and carbon nanotube/CMC composites capable of sensing low, down to 20 ppm and 6 ppm, NO₂ concentration respectively. The new sensors show selectivity to NO₂ because of the selective oxidation of the composite component CMC salt by NO₂. Due to the Solubility of CMC in water and response of the sensor to ppm-level NO₂, a washable textile-based NO₂ sensor based on a reduced graphene oxide/MoS₂ composite material was developed. The sensor has selectivity to NO₂ and can detect ultra-low (100 ppb) NO₂ concentration levels in >60% humid air. It can also detect down to 20 ppb NO₂ in dry air. The next objective, beyond the scope of this work, is to integrate both PM₂.₅ and NO₂ detection and monitoring. Commercial exploitation of the technologies developed is now being explored through a University spin-out.
Sensors, Air pollution
Federal Government of Nigeria through the Presidential Special Scholarship for Innovation and Development (PRESSID) administered by the National Universities Commission (NUC) and funded by Petroleum Technology Development Fund (PTDF) Engineering and Physical Sciences Research Council (EPSRC) through the Sensors CDT.
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This record's DOI: https://doi.org/10.17863/CAM.54901
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