Modelling and Simulation of a portable, size-discriminating Capacitive Particulate Matter sensor

Abstract

© 2019 IEEE. Air pollution causes premature deaths and increased infant mortality. [1] Particulate Matter smaller than 2.5μm in aerodynamic diameter (PM2.5) exposure has been found to be the cause of airway inflammation and other adverse effects. [2], [3] Recent studies have shown that vehicular emissions are even more harmful for children on the roadside. [4] In fact, personal exposure has been found to be dependent on routes taken and transport modes. [5] Hence, air pollution mitigation strategies must be adapted in each location based on the emission sources. [6] A study in Brazil has estimated 400-1700 premature deaths to have been prevented by reducing deforestation, an important source of PM2.5. [7] This approach requires the use of portable sensors to provide high resolution data than obtained in stationary stations. However, smaller sensors are less accurate than the bulky static detectors. [8] Most commercially available portable PM sensors are based on light. But there has been problems with unit to unit deviation and inaccurate measurements. [9] Hence there is a need for portable, yet accurate PM sensors suitable for personal exposure monitoring. This work shows that the statistically relevant information on size distribution of particulate matter entrained in inhalable airflow can be obtained from miniaturised capacitive sensors using thermophoresis. Hence, the impact of a thermal gradient on the particles causes different sizes to separate into different streams and are deposited on corresponding electrodes and detected as capacitive jumps caused by the increase in the dielectric constant of the volume space occupied by the deposited particle. These results were obtained from modeling and simulation of the sensor using COMSOL Multiphysics® modules for computational fluid dynamics, heat transfer, particle tracing and electrostatics and were validated by comparing the simulation results with literature. This possibility to monitor different size ranges at such single particle scale in a portable device suitable for personal exposure studies is extremely important for the development of sensors suitable for non-intrusive personal exposure studies. This is because they provide high resolution measurements that account for spatiotemporal variations in air quality during its period of use in mobile conditions. The method can also be further miniaturized and integrated into MEMS as additional work anticipated elsewhere[10]. More representative information on air pollution will help to enhance the effectiveness of mitigation approaches