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A real-time fine particulate matter monitor based on inertial size-separation and optical detection in a microchannel

University of British Columbia

Exposure to fine particulate matter smaller than 2.5 μm in diameter (PM 2.5) is linked to increased mortality and morbidity. The real-time monitoring of PM 2.5 has important applications in indoor and outdoor air quality monitoring including occupational environments. However, commercially available real-time instruments are bulky and expensive, not suitable for personal exposure level monitoring. This thesis presents a real-time, miniaturized PM 2.5 monitor which consists of a microfluidic-based particle trapping impactor and a forward light scattering optical detector with a 3D-printed housing. The particle trapping impactor channel includes a 90° turn, where larger particles experience a greater inertial force and enter and become captured in the particle trapping region. The detector, positioned downstream from the separator, illuminates the sized particles with a focused laser beam and detects light scattered by the particles using a photodiode to obtain the particle count. The baseline geometry of the impactor is designed according to conventional impactor design methods and analytical calculations. The geometry is further optimized through an iterative process by simulating the flow velocity and particle behavior in the microchannel to obtain the sorting efficiency. The fabricated impactor channel is tested by transmitting particles from 0.5 to 3 µm through the device and is shown to have a 50% cut-off diameter of around 3 µm. The experimental sorting efficiency curve agrees with simulation-based predictions. The arrangement of the detection system is optimized based on Mie scattering intensity and ray tracing calculations. Inexpensive, commercially available components are selected by modeling the optical power of scattered light on the photodiode surface. The detector is tested in parallel with a commercial instrument and shows good correlation at 1 minute sampling interval for 2 µm particles. The measured pulse peak voltage and pulse width agree with the theoretical calculations. The integrated device requires a 10 minutes sampling time for a statistically significant measurement due to particle loss at the interface between the separator and detector. The experimental results demonstrate the potential of using microfluidics as a platform for a low-cost, real-time portable PM 2.5 sensor.

Text

2016-04-30

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/52832

Mechanical Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/