To achieve real-time monitoring of aerodynamic submicron particle size distributions at a point-of-interest, we developed a high-performance particle size spectrometer that is compact, low-cost, and portable. The present system consists of four key components: a unipolar mini-discharger for electrically charging particles, an inertial size-separator for classifying charged particles into five size fractions in terms of their aerodynamic sizes, a portable multi-channel electrometer for detecting femto-ampere currents carried by charged particles at each stage, and a retrieval algorithm for converting the current data into a smooth particle size distribution. The unipolar mini-discharger and inertial size separator were quantitatively characterised by using standard polystyrene latex (PSL) particles. The experimentally determined cut-off diameters at each stage in the inertial size separator were 1.17, 0.94, 0.71, 0.54, and 0.23 μm, respectively. Then, the system was compared with a commercial reference aerodynamic particle sizer (APS) in the environment where the number concentration and the average size of TiO2 particles were changing. The present system resolved peak size and geometric standard deviation of particles to within 11.2%, and 6.3%, respectively, indicating that the system can be used to accurately monitor submicron particle size distributions in real time.
Abstract. We present a portable, inexpensive, and accurate
microelectromechanical-system-based (MEMS-based) condensation particle counter
(CPC) for sensitive and precise monitoring of airborne ultrafine particles
(UFPs) at a point of interest. A MEMS-based CPC consists of two main parts:
a MEMS-based condensation chip that grows UFPs to micro-sized droplets and a
miniature optical particle counter (OPC) that counts single grown droplets
with the light scattering method. A conventional conductive cooling-type
CPC is miniaturized through MEMS technology and three-dimensional (3-D)
printing techniques; the essential elements for growing droplets are
integrated on a single glass slide. Our system is much more compact (75 mm × 130 mm × 50 mm), lightweight (205 g),
and power-efficient (2.7 W) than commercial CPCs. In quantitative
experiments, the results indicated that our system could detect UFPs with a
diameter of 12.9 nm by growing them to micro-sized (3.1 µm) droplets.
Our system measured the UFP number concentration with high accuracy (mean
difference within 4.1 %), and the number concentration range for which
our system can count single particles is 7.99–6850 cm−3. Thus,
our system has the potential to be used for UFP monitoring in various
environments (e.g., as an air filtration system, in high-precision industries
utilizing clean rooms, and in indoor and outdoor atmospheres).
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