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A new technique for continuously monitoring both the size and optical properties of individual airborne particles could offer a better way to monitor air pollution. It is especially promising for analyzing fine particulate matter measuring less than 2.5 microns (PM2.5), which can reach deep into the lungs and cause health problems.
[...] For the new analysis approach, airborne particles are trapped inside a laser beam by optical forces and propelled forwards by radiation pressure. The trapping force is strong enough to overcome the gravitational force acting on very small particles such as PM2.5 and automatically aligns the particles with a hollow-core photonic crystal fiber. These special fibers feature a central core that is hollow and surrounded by a glass microstructure that confines light inside the fiber.
Once aligned, the laser light propels the particle into the fiber, causing the laser light inside the fiber to scatter and createe a detectable reduction in the fiber transmission. The researchers developed a new signal processing algorithm to retrieve useful information from the particle-scattering data in real-time. After detection, the particle simply ejects from the fiber without degrading the device.
"The transmission signal from the fiber also lets us measure time-of-flight, which is the time the particle takes to travel through the fiber," said Abhinav Sharma, the doctoral student working on this project. "The drop in fiber transmission together with the time-of-flight information allow us to unambiguously calculate the particle size and refractive index. The refractive index can assist in identifying the particle material because this optical property is already known for most common pollutants."
Journal Reference: Abhinav Sharma, Shangran Xie, Richard Zeltner, Philip St.J. Russell. On-the-fly particle metrology in hollow-core photonic crystal fibre. Optics Express, 2019; 27 (24): 34496 DOI: 10.1364/OE.27.034496
(Score: 2) by bd on Saturday November 16 2019, @12:20PM
They make it sound as if real-time, or near real-time particulate matter monitoring is somehow difficult and error-prone (it has been done since the 1980's), in order to make their overcomplicated, most likely overexpensive setup sound reasonable.
Also, it is not practical at all:
They prevent clogging of the fiber using a filter. Filters introduce large errors. If you are in a place where there is an actual health concern, this filter will also clog up.
If there is mist in the air, the filter will get wet. This will affect the size of particles it catches.