Design And Application Of Portable Multipass Optical Absorption Cell

With the rapid development of society economic, emissions from factories, exhaust from motor vehicles and coal-fired power generation etc. produce a large number of inhalable particles(PM10). When the concentration of inhalable particles(PM10) in the air exceeds the air pollution index, it not only reduces the visibility of the atmosphere, but also threats the health of human. Therefore, it is important significance to monitor the concentration of particulate matter in the air. There are many kinds of methods detecting the concentration of particle matters at present, such as microscope method, weighing method, light scattering method etc. Among them, light scattering method has become a hot research topic because of its wide range of response, high precision and fast measurement.Usually, the concentration of inhalable particles in the air is small(less than 0.35?g/L), and the light intensity change little caused by scattering effect. This paper proposes a spiral type portable multipass optical absorption cell based on the structure characteristics of various multipass cells, to increase the effective optical path of light and the interaction of particles. The optical device consists of multiple torus concave mirrors in a spiral route. Incident light propagates along with radical and axial direction, and shows winding staircase pattern. The faculae on the inner wall present a spiral-type. The entrance and exit apertures are separated due to the spiral trace of optical rays, which increases the accessible adjustment of the apparatus. The effective optical length can be adjusted in accordance with the proportional relationship to the reflective times. This device is characterized with easy adjustment and excellent mechanical performance due to its cylindrical structure. Furthermore, we introduce two preconditions of reflected beam convergence in the cell and studying the characteristics of its rotation.In addition, the reflection of beam is simulated between two concave mirrors with curvature radius of 400 mm according to the structure of Herriott cell. Finally, we select the base length of 304.64 mm, the effective length of Herriott cell is 15841.3mm. Then a vacuum device of portable Herriott multipass optical absorption cell is processed for measuring the concentration of PM10 in the air. In the experiment, laser with three wavelengths output is used to realize the Mie scattering between PM10 and three different wavelengths of light in the Herriott cell. The dependence of the output intensity and wavelength is obtained in combination with the output of photo detector and Mie scattering theory. Particle sizing in polydisperse system is equivalent to particle sizing in Single disperse system base on the average particle size of Sauter method, and deriving the average size of inhalable particles. And the computational process of Mie scattering extinction coefficient is described. Finally, the PM10 concentration in the air is measured and the distribution diagram of particle size is drawn based on the average particle size and extinction coefficient. At the same time, the PM10 concentration is measured by weighing method. The results show that the PM10 concentration measured by the three wavelength Mie scattering experiment is close to that of the weighing method.