An integrated electrical condensation particle counter for compact and low-cost ultrafine particle measurement system

In this study, we developed a compact and low-cost measurement system that can measure the real-time number concentration of airborne ultrafine particles (UFPs, particles smaller than 100 nm). Our system is based on the condensation nucleation method; however, it counts particles based on their electrostatic properties (i.e., dielectric constant) to overcome the limitations of complex optical systems that have traditionally been employed. The new system consists of two components: a microfluidic particle growth channel to grow UFPs into micron-sized water droplets and a capacitive particle counter to count the grown droplets. To effectively reduce the size and cost of the system, each system was fabricated into a single module using a semiconductor manufacturing process prior to integration. Super-hydrophilic micropillar wicks were monolithically integrated with Printed Circuit Board substrate channels to use water as the condensing working fluid. A glass substrate interdigitated electrode chip with a 3 μm gap was fabricated and placed on the impaction plate of an inertial impactor to be used as a sensor. Numerical calculations were performed to verify the dimensions of the channel required for efficient supersaturated vapor generation. Quantitative experiments using NaCl, (NH₄)₂SO₄, and Ag₂O UFPs showed that our system could grow particles larger than 50 nm into micron-sized droplets and count up to 10,300 N cm⁻³ particles with linear electrostatic properties.