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Stationary source emissions of key industries, such as thermal power plants, have become the central consideration in environmental protection programs. Existing photoelectric sensors at stationary sources usually use a single wavelength laser to measure the total mass concentration of the particulate matter, bearing inherent errors due to the changing particle size distribution (PSD). However, the total mass concentration cannot comprehensively estimate the air pollution caused by the stationary sources. Therefore, it is required to measure both the mass concentration and PSD of the aerosols emitted by the stationary sources, based on which we can get a distributed mass concentration. To implement this, in this study, we designed a novel three-wavelength photoelectric sensor and tested its performance. Results showed that the prototype correctly determines the mean particle size and standard deviation of the PSDs and consequently adjusts the coefficient for measuring the mass concentration from light intensity, providing a comprehensive assessment of the pollutants.

Aerosol plays an important role in a broad range of scientific disciplines, such as atmospheric chemistry and physics, fuel combustion, and human health. Current particle sizing instruments are usually bulky, complicated, and expensive, while the portable ones cannot provide sufficient measurement channels to describe the particle size distribution accurately. To address this challenge, we propose an optical sensing method to analyze the particle size distribution of aerosols based on the light scattering intensity field (LSIF). The LSIF is a set of scattering lights in all directions around the particles, which contains the scattering light signals in different observing angles. Then, the particle size distribution of the aerosol samples is retrieved by the Tikhonov regularization algorithm. A portable and low-cost aerosol sizing prototype sensor is designed to image part of the LSIF signals, where the LSIF is collected by a parabolic reflector and projected on the image sensor as an image with telecentric lenses. According to the experimental result of di-ethyl-hexyl-sebacate aerosol test, the relative measurement error of LSIF can be controlled to ±10%. With an integrated and cost-effective design, this particle sizing sensor shows great potential for routine field measurements outside of the laboratory.

Mass concentration is a commonly used but insufficient metric to evaluate the particulate matter (PM) exposure hazard. Recent studies have declared that small particles have more serious impacts on human health than big particles given the same mass concentration. However, state-of-the-art PM sensors cannot provide explicit information of the particle size for further analysis. In this work, we adopt Sauter mean diameter (SMD) as a key metric to reflect the particle size besides the mass concentration. To measure SMD, an effective optical sensing method and a proof-of-concept prototype sensor are proposed by using dual wavelengths technology. In the proposed method, a non-linear conversion model is developed to improve the SMD measurement accuracy for aerosol samples of different particle size distributions and reflective indices based on multiple scattering channels. In the experiment of Di-Ethyl-Hexyl-Sebacate (DEHS) aerosols, the outputs of our prototype sensor demonstrated a good agreement with existing laboratory reference instruments with maximum SMD measurement error down to 7.04%. Furthermore, the simplicity, feasibility and low-cost features of this new method present great potential for distributed PM monitoring, to support sophisticated human exposure hazard assessment.