Lab-on-printed circuit board based water harvesting condensation particle counter for ubiquitous monitoring of airborne ultrafine particles

Abstract

We have developed a water harvesting condensation particle counter (WHCPC) using lab-on-printed circuit board (PCB) technology. Our method provides an inexpensive, compact, and highly accurate system for the ubiquitous monitoring of airborne ultrafine particles (UFPs). Lab-on-PCB-based WHCPC uses water as the working fluid to monitor harmless UFPs; it does not require water replenishment using a moderated water condensation method. Lab-on-PCB-based WHCPC consists of two main parts, a UFP growth section and a mini-OPC, through which UFPs are grown into micro-sized droplets and the grown droplets are single-counted. The UFP growth section consists of two PCBs and a 3D-printed channel. The heater, temperature sensor, and hydrophilic micropillar array wick, which are essential for the growth of UFPs, are integrated on the PCBs. Simulations were performed to verify the saturated-air generation and water collection in the UFP growth section. The dew points of the inlet and outlet air samples were measured to verify water collection using the moderated water condensation method. Through quantitative experiments using UFPs artificially generated in the laboratory, particles of 9.4 nm could be counted. It was possible to precisely measure the number concentration (2500–270000 N cm−3) over a wide range. In addition, the stability of the proposed system was confirmed through a long-term comparison with the reference CPC in an outdoor environment. The proposed system realized the sensorization of CPC because it could monitor harmless UFPs, with minimal maintenance; the proposed system is also inexpensive and compact.