The Study Of Atmospheric PM2.5 Concentration Based On Side-scattering Echo Signal

In this paper,we made the following research about the side-scattering lidar and atmospheric PM2.5 concentration inversion mechanism:(1)The background and significance of PM2.5 research and several mainstream methods and principles of concentration measurement are introduced,and the current research situation of lidar and atmospheric exploration at home and abroad is described in detail.(2)The propagation characteristics and physical parameters of gaussian beam in the atmosphere are introduced.The composition of atmospheric aerosols and three scattering modes between laser and aerosol are described.Then the mie scattering theory of single spherical particles on the laser is described emphatically.(3)The Monte Carlo scattering model is established,the parameters of the Monte Carlo simulation method based on the light intensity distribution of the side-scattering echo signals are set strictly according to the parameters of the experimental device.Different calibration factors g are set in the Monte Carlo program,the distributions of light intensity and SPF corresponding to different g from simulation are compared with the experimental measurement results,when g is taken as 0.9,the consistency between the two results is good.Then,taking g from 0.86 to 0.95 at intervals of 0.01,ten simulation results show that the total number of photons on the receiving detector is nearly proportional to the number of times scattering between photons and particles.At the same time,takeing 220 experimental datas collected,fitting T(0)and PM2.5 concentration relationship,the results are in good agreement with the simulation results.Therefore,the method is very suitable for simulating the light intensity distribution of atmospheric aerosols when the laser side-scattering lidar is emitted horizontally,in particular,providing guidance for designing PM2.5concentration-related characteristic value S(i)algorithm.(4)A CCD side-scattering lidar experimental system has been set up,set the CCD at different gains,using the system to complete the acquisition,BAM-1020 air quality detector recording the PM2.5 concentration at the same time.S(i)is the total light intensity distribution that extracted from the echo signals,Fitting a large number of data points between S(i)and PM2.5 concentration values to obtain ten fitting results and empirical formulas.The fitting results show that the S(0)and S(20)inversion models are more suitable for inversing values of PM2.5 concentration when CCD were low gain,and the inversion models of S(0),S(20),S(40),S(60)and S(80)can all be used for accuratly inversing values of PM2.5 concentration when CCD were high gain.Then the PM2.5particle concentration measured by BAM-1020 was taken as the standard reference value,and the measurement error of each grade S(i)inversion model is analyzed based on statistical parameters such as average error,residual variance and comprehensive deviation rate.The results of the analysis confirm the gain and grade i values of the best inversion accuracy model,When the concentration of PM2.5 is in the range of 0-70μg/m~3,the inversion accuracy of the S(i)inversion model at high gain of the CCD is higher than that of the S(i)inversion model at low gain of the CCD,and when CCD at high gain,and i=20 level of inversion has highest accuracy.(5)An all-weather PM2.5 concentration real-time detection device based on the side-scattering lidar was designed and the combination methods of each unit in the device and the operation method of the experiment were given.Draw a real-time curve of the PM2.5 concentration values retrieved and calculate its rate of deviation,compared with a small air quality detector on the market and the experimental device that is not installed in the test box.The results show that the all-weather real-time detection device can well eliminate the effect of air humidity on the concentration of PM2.5 inversed,and has obvious advantages in accuracy.