Aerosol Detection Based On Cavity Ring-down Spectroscopy Technique

Aerosols are the main component of air pollution and the main factor affecting solar radiation and climate change.As an important component of atmospheric visibility,the extinction coefficient of aerosols is of great significance in atmospheric transport calculations,climate change research,air-to-ground observations,and aviation safety.As a rapid detection spectroscopy technique,cavity ring-down spectroscopy has the advantages of high sensitivity and strong selectivity,and is an effective means to study the extinction characteristics of aerosols.In this paper,theoretical and experimental researches on aerosol cavity ring-down spectroscopy detection technology are carried out,which mainly include the following contents:1.The measurement principle of cavity ring-down spectroscopy is studied and analyzed.Starting from the photo-bullet model and the principle of multi-beam interference,the time-domain and frequency-domain characteristics of the laser beam in the linear cavity are analyzed,and the characteristic parameters and expressions that determine the performance of the ring-down cavity are summarized;the ring-down characteristics and the Gaussian beam in the cavity are analyzed.It provides a theoretical basis for the design of the ring-down cavity.The mode matching in the cavity is studied,and a solution to the cavity mismatch and cavity mismatch problems during the matching process between the laser and the ring-down cavity is proposed.2.The whole process of cavity ring-down is studied based on the dynamic energy angle.The energy change process in the cavity during the continuous wave cavity ring-down measurement is analyzed.Aiming at the charging process of the current-modulated cavity ring-down,an injected light intensity model based on the wavelength scan rate is established,and the current-modulation detuning turn-off is explained.time overcharge.Experiments show that changing the threshold and delay time can improve the detection accuracy,which verifies the simulation of the charging time.Increasing the threshold will gradually reduce the data acquisition rate of the ring-down process.When setting,the detection efficiency must be taken into account on the premise of satisfying the detection accuracy;increasing the appropriate delay time can improve the ring-down time and detection accuracy,and achieve high-precision sampling.3.The experimental study of cavity ring-down spectroscopy aerosol extinction was carried out.The components and key process of building a cavity ring-down spectrometer are introduced,and the simulation and experimental debugging process of the mode matching and shutdown system are introduced in detail.Through the calibration measurement and performance characterization of the instrument,the background ring-down time is 38.29μs,the standard deviation is 0.62μs;the baseline drift value in the long-term measurement is2.1084×10^-8 m^-1,and the minimum extinction detection limit is 2.0843×10^-6 m^-1,the aerosol detection device has excellent performance.The experiment can obtain the ring-down time and extinction coefficient of different aerosol particle sizes,and realize the rapid online detection of aerosol extinction coefficient.During data processing,the"sampling"and"average"of the data acquisition part are also analyzed,and a single sampling can more accurately represent the error in data acquisition.