Modelling for Estimating Aerosol Particle Size from Laser Light-Scattering Measurements
The need to measure aerosols has increased dramatically over the last few decades in various fields including public health, atmospheric science, nano-technology, chemical manufacturing, pharmaceuticals, medicine, and specially air pollution.
NILU is developing a Wearable particle detector, LeoPard, allows for high-precision monitoring of aerosols particle exposure of industrial workers.
Leopard is a sensor/alarm device carried by workers in the production industry. It will alert the wearer in cases exceeding limits for both peak and accumulated exposure. Therefore, it is important to control and measure aerosol particle size.
To do such job, the LeoPard device, which is based on Single Particle optical Counting (OPC), is being developed at NILU for measurements of aerosol concentrations and size distributions. OPC-based aerosol particle counters are used to determine the air quality by counting and sizing the number of particles in the air. The instrument principle is utilizing a light source (typically a plasma laser or laser diode) collimated to illuminate a sample volume of aerosol flowing out of a nozzle; a photodetector, off-axis from the light beam, measures the amount of light scattered from single particles by refraction, reflection and diffraction. Both the size and the number of particles are measured simultaneously.
Determination the particle size from the instrument response to single particles is challenging because of the complicated dependence of the response on particle size, particle index of refraction, particle shape, lens geometry of the counter optical system.
Therefore, developing a model to determine particle size from scattered light measurements is important. To estimate correctly with high accuracy, the mathematic model should take account all numerous factors that contribute to scattering intensity, such as the distance to the particle, the scattering angle, the refractive index of the particle, the optical system characteristics…