Detection And Correlation Analysis Of Atmospheric Aerosol And VOC Based On Lidar And PTR-MS

The content of aerosol in the atmosphere is relatively small,and from the time of large-scale spanning,the generation and disappearance of aerosol particles are in a dynamic equilibrium,and the natural source is the dominant factor.However,in recent years,with the development of various industries and the acceleration of urbanization,the leading role of human activities in urban areas is becoming more and more obvious,and various atmospheric environmental problems are common.Atmospheric aerosol has the characteristics of uneven distribution and small variation scale.The near-surface aerosol is closely related to human activities and has important effects on human health,climate and traffic safety.In the study of atmospheric aerosols,the observation methods of aerosols mainly include direct detection and remote sensing detection.Direct detection is the use of in-situ measuring instruments and methods such as ground base stations,sounding balloons,and aircraft mounting.Lidar is an active atmospheric remote sensing detection tool in optical frequency band.It has the advantages of extremely high angular resolution,temporal and spatial resolution,wide detection range,small disturbance to the atmosphere,long-term continuous monitoring and real-time data acquisition,etc.Physical parameters and environmental detection have been widely used.Through the detection and analysis of the echo signal after the emitted narrow pulse laser interacts with atmospheric molecules and aerosols on the transmission path,the parameters such as the temperature,humidity,and extinction coefficient of the measured area can be obtained.Vertical aerosol extinction coefficient profile is the key to evaluating the aerosol radiation effect,what’s more,it is also the premise of indirect inversion of fine particulate matter(PM_2.5)concentration from lidar signal.Volatile organic compounds（VOC）,as precursors of aerosol and Ozone（O₃）,have become substances that urgently require coordinated control.Therefore,the detection of aerosols and volatile organic compounds is of great significance.The main research work of this article is divided into the following aspects:（1）In this paper,Charge Coupled-Device（CCD）camera and back scatter lidar are proposed to realize the detection of aerosol extinction coefficient in a wide range and without blind area.The accurate lidar ratio is obtained by using Mie channel and Raman channel.The relative error and the height resolution of the side scatter lidar are analyzed,and the backscattering signal of the side-scatter lidar and the back-scatter lidar are stitched together.（2）A side-scatter lidar system composed of a horizontally placed CCD camera and two vertically placed CCD cameras with different horizontal distances is used to obtain the optimized phase function,and then the accurate aerosol extinction coefficient is obtained by reverse calculation.（3）The relative humidity segmentation method is proposed for the conversion between the extinction coefficient of aerosol and the concentration of fine particulate matter.The segmentation standard is as follows:when the relative humidity is lower than 75%,the exponential fitting model is used for the conversion of aerosol extinction coefficient and PM_2.5concentration.On the contrary,when the relative humidity is higher than 75%,the linear fitting model is used.The variation trend of the fitted PM_2.5concentration and the PM_2.5concentration measured by field instruments showed a high correlation.The correlation coefficient reached0.850.Then,the fitting model in this paper is compared with the fitting model proposed by Zhang et al.The PM_2.5concentration fitted by the two methods is in good agreement with the PM_2.5concentration measured by field instruments.The correlation coefficients are all above0.889,which further proves the rationality of the relative humidity segmentation method.（4）In this paper,the vehicle differential absorption lidar（DIAL）and Proton Transfer Reaction Mass Spectrometry（PTR-MS）system were used to detect the volatile organic compounds,fine particulate matter and ozone emission sources in the environment in real time.The echo signals of 289 nm and 299 nm wavelength of differential absorption lidar were selected to invert the vertical distribution profile of O₃concentration,and the echo signals at 316nm wavelength were selected to invert the extinction coefficient of aerosols.The differential absorption lidar and proton transfer reaction mass spectrometer were mounted on the vehicle platform,and the three-dimensional distribution characteristics of environmental VOC,particulate matter and O₃were obtained by plane scanning,navigation detection and vertical fixed detection methods.Combined with the vehicle GPS data,the precise traceback of pollutants was realized.