Research On Humidity Correction Of Light Scattering Aerosol Mass Concentration Measurement System

The light scattering method has the advantages of on-line and non-contact measurement,which makes this method plays a pivotal role in the field of aerosol mass concentration monitoring.However,it is susceptible to the relative humidity during real-time monitoring.In order to improve the accuracy of real-time monitoring by light scattering method,the dependence of aerosol particle mass concentration and relative humidity has been figured out,through combine the theory and experiments in this study.And the main results are as follows:Firstly,the hygroscopic growth models of single-particle hydrophilic and hydrophobic aerosols were established by using the principles of thermodynamics and surface adsorption,respectively.Based on which,the two-particle and multi-particle aerosol growth models were established.By using the discrete dipole approximation method,the scattering characteristics of the above aerosol model under different relative humidity are calculated and analyzed,and the variation law of the scattered light flux of the multi-particle condensed aerosol with the particle size is obtained.The involved results provide theoretical support for humidity correction of calibration parameters in the concentration inversion model.Secondly,for the optical sensor,a multi-channel circuit is designed to collect and process the light signals scattered by the particles.This circuit uses FPGA to control the high-speed ADC for data collection and classify according to the voltage value.And then,the data is input to STM32 which transmits the collected voltage signal amplitude distribution and corresponding humidity value data to the PC host computer for real-time saving and calculations.Finally,the soot particles are used as samples,and the optical sensors are calibrated and tested in a humidity range of 40% to 90%.Combined with the relationship between the scattered light flux and particle size of condensed particles at different humidity calculated by the discrete dipole approximation method,a humidity correction method for the calibration parameters in the aerosol mass concentration fractal inversion model is given.The corrected calibration parameters were used to measure the aerosol mass concentration at high humidity.It was found that the average relative error between the mass concentration value and the standard value retrieved before the correction was up to 19.16%.The average relative error of the mass concentration is within 9.07%.It can be seen that the measurement accuracy of the corrected soot aerosol mass concentration has been improved significantly,and the problem of low real-time measurement accuracy of the light scattering method aerosol mass concentration under high humidity conditions is solved.The research in this paper is in line with the national current requirement for real-time monitoring of the atmospheric environment,and has important reference value for controlling atmospheric pollution,protecting human health,correctly understanding the attenuation law of atmospheric visibility and global climate change.