A low-cost instrument for environmental particulate analysis based on optical scattering

This paper presents the design, realization and calibration of a portable instrument for real-time measurement (concentration and size distribution) of airborne dust particles. The measuring principle is the estimation of the light scattered by the particles under illumination. The proposed design is characterized by low hardware cost and simplicity of calibration but, nevertheless, it delivers significant performance in terms of size resolution. This result could be achieved by means of an accurate processing of the detected signal, which maximizes the signal/noise ratio in detecting the scattering peaks. In order to get this signal processing chain running in real time on a low-cost platform (an ARM7-based microcontroller board), computationally efficient algorithms have been developed for optimal filtering and peak detection. For the metrological calibration of the instrument, a simple method is proposed, which employs commonly available materials with known particle size distribution, instead of expensive monodispersed test particles. The experimental results show the effectiveness of the proposed calibration and the ability of the instrument to reach a sensitivity and a granulometric resolution comparable to those of more sophisticated instruments.