In situ optical sensor for aerosol ovality and size

Abstract

Sensors for in situ detection of aerosols using conventional optical scattering methods generally fail to identify the types and sources of particles, and they even have a large discrepancy in particle size measurements because the particles are overly simplistically assumed to be spherical. To address this issue, we investigate the effects of particle shape on light-scattering patterns and develop a portable sensor that can simultaneously determine the particle shape and size. To describe all particles, particularly irregular particles with a generalization parameter, we define ovality to represent the properties of particle shape, which is a distinctive feature related to particle type and source. Furthermore, we analyze the multi-angle light-scattering patterns that vary for particles of different shapes and sizes. On this basis, a sensing method is proposed to simultaneously determine the ovality and size of particles by jointly assessing the light-scattering pattern features. Finally, an 8-channel sensor is developed and tested with di-ethyl-hexyl-sebacate (DEHS) aerosol, Duke particles, and N-Heptane combustion smoke. The DEHS aerosols are used for the calibration of our sensor. The average error of the shape and size of Duke particles determined by the experimental measurements of our sensor is 4.01 %. The measurement error of N-Heptane compared to an ellipsoid with an ovality of 15:1 is 5.84 %. The experimental results show that our sensor has the potential to measure the properties of particle shape to identify the types and formation mechanisms of aerosols. • The effects of particle shape on light-scattering patterns are investigated. • The conventional calculation algorithm is improved according to the geometric properties of the shape determined by our sensing method, for combustion smoke and other examples that deviate greatly from the spherical shape. • A portable sensor that can simultaneously determine the particle properties and size is developed. • Extensive experiments are repeated for proving that the developed sensor is highly portable and suitable for aerosol measurement.