Study On Detection Techniques And Experiments Of Biological Aerosols In The Atmospheric Boundary Layer By Fluorescence Lidar

As an important part of atmospheric aerosols,biological aerosols can cause acute chronic diseases in plant and humans by diffusion and spread in the atmosphere.Biological aerosols can also alter g,lobal climate indirectly and show potential sig,nificant impact on atmospheric chemistry and physical processes.The real-time detection technology on the basis of atmospheric biolog,ical aerosol optical properties shows important academic and scientific value for detection of biological aerosol concentration and spatial-temporal distribution pattern in the atmosp here.As a long-range active remote sensing tool,fluorescence lidar provides an effective research tool for early warning and rapid detection of potcentially harmful biological aerosols in the atmosphere.In this paper,we studied the detection technology of fluorescence lidar in the atmospheric boundary layer.According to the dependence between the intensity and relative content of atmospheric biological aerosol fluorescence,we explored the key technique to invert biological aerosol concentration in the atmospheric boundary layer.Then we designed and developed a fluorescence lidar system,and performed continuous and long-term experimental research on atmospheric biological aerosols in Xi'an city,verifying the detection performance and feasibility of the system,as well as obtaining atmospheric biological aerosol fluorescent signal corridors.Furthermore,the correlation between biological aerosol number concentration and aerosol extinction coefficient in the atmospheric boundary layer was analyzed.Based on the detection principle of fluorescence lidar,the effective detection range of the lidar system for atmospheric biological aerosol was simulated.Within the range of error less than 10%,the minimum detection concentration of biological aerosol was evaluated with distance variation,and the effects of system device parameters,experimental environment and biological aerosol particle parameters on the detection performance of fluorescence lidar system were further analyzed.Based on the numerical simulation of the system,the detection performance of the biological aerosol early warning fluorescence lidar system was studied.By increasing the cumulative number of fluorescence signal acquisition,the recognition distance and the minimum detection concentration of the fluorescentce lidar system were improved.A fluorescence lidar was developed to continuously observe the atmospheric biological aerosol fluorescence signal(310-440 nm),and to further obtain the temporal and spatial characteristics of biological aerosol fluorescence signal in the Xi'an urban boundary layer.Based on the Mie-Rayleigh scattering lidar equation and the fluorescence lidar equation,the Mie-Rayleigh scattering echo signal collected by the lidar system was inverted to get the extinction coefficient of the excitation wavelength in the air,and then the extinction coefficient of the fluorescence wavelength in the atmosphere is obtained.The concentration of biological aerosol in the air was inverted using the known fluorescence cross-section parameters as reference values.For the first time,a continuous observation experiment of atmospheric biological aerosol concentration was conducted over the Xi'an area using a lidar,and the spatial distribution of the atmospheric biological aerosol concentration in the atmosphere at the bottom was continuously changed with time.A long-term continuous observation experiment was conducted to study the characteristics of the biological aerosols and aerosols,and to analyze the vertical variation of the fluorescence mixture ratio and the distribution characteristics of biological aerosols in different seasons.The ratio of the fluorescence signal to the intensity of the Mie-Rayleigh scattering signal was analyzed to reveal the temporal and spatial characteristics of the proportion change of the biological aerosol in the air.Simultaneous and continuous observations of biological aerosol concentrations and aerosol extinction coefficients over the Xi'an urban area were conducted to study the association characteristics between atmospheric biological aerosols and aerosols in the process of aggregation,distribution,and transmission.Seasonal concentration distribution of biological aerosol over the Xi'an region was observed using a fluorescent lidar.Based on the long-term experimental measurement data,combining with the PM2.5 and PM10 collected real time by the meteorological department,we explored the seasonal characteristics of atmospheric biological aerosol.It is difficult for long-wavelength lidar to detect the atmospheric aerosols as it is sensitive to the background of solar radiation.For the first time,we utilized the Mie scattering lidar with the wavelength of 266 nm to conduct continuous observation of biological aerosol on the atmospheric boundary layer over the Xi'an urban area.Utilizing the 266 nm lidar in the ultraviolet region,we performed continuous observation and research of the vertical variation characteristics of the aerosol extinction coefficient in the boundary layer over the Xi'an urban area.Then we compared the inversed data collected from lidar with the information provided by the real-time monitoring stations of the local meteorological department,it proved that these two have good consistency.The continuous change of aerosols over the 24-hour period is shown by the THI map,which provides new reference data for studying the overall trend of atmospheric aerosols in Xi'an urban area.