Inherently Charged Particle (ICP) Sensor Design

Ambient particles from natural and anthropogenic sources are a major cause of premature deaths globally. While there are many instruments suitable for scientific measurements of aerosols, better methods for long-term monitoring purposes are still needed, especially low-maintenance, affordable solutions for ultrafine particles. In this article, we present a new sensor design and prototype, the inherently charged particle (ICP) sensor, which uses the preexisting electrical charge of particles to measure particle concentration, instead of employing a charging mechanism, as is typical for instruments based on electrical detection. When the ICP-sensor is employed in conjunction with another instrument, information on the particle charge state can also be derived. We present the results of a laboratory characterization as well as two measurements in suggested applications: 1) engine exhaust measurements and 2) ambient measurements in a traffic environment, where we compare the sensor response to three particle concentration metrics: 1) number; 2) surface area; and 3) mass. The sensor proved suitable for both applications, the signal correlated best with number concentration in the engine emission measurements and with particle surface area in the ambient measurements. The measured charge concentrations were well-correlated ( ${R}^{\,2} >0.8$ ) with theoretical values calculated from the number size distribution assuming an equilibrium charge distribution.