Development And Applications Of Aerosol Extinction Spectrometer Based On Cavity Ring Down Spectroscopy

Aerosol particles are the major component of urban pollution. They influence climate directly by scattering and absorbing of incoming solar radiation and indirectly by acting as cloud condensation nuclei. Recently, much attention has been paid to the global estimate of direct radiative forcing, due to aerosols. Hence, accurate determination of aerosol extinction is crucial for reducing uncertainties of estimated radiative forcing caused by aerosol. Cavity ring-down spectroscopy(CRDS) technique, which benefits from its long effective path length in absorption, and has the advantages of high sensitivity and low detection limit, is commonly recognized as one of the best candidates to measure the extinction coefficient of aerosol.In the present work, the technology of aerosol extinction spectrometer based on the CRDS theory was expounded and a high performance aerosol extinction spectrometer used to measure the actual atmospheric aerosol extinction coefficient was established. The performances of aerosol extinction spectrometer were characterized, and the aerosol extinction characteristic and its diurnal pattern around yangcheng lake, kunshan, was analyzed in detail through a long-term observation.The main merits and innovations of this thesis are as follows:(1) The aerosol extinction spectrometer for the aerosol extinction characteristic measurement based on the CRDS technology developed in our team was the first one in China. After aerosol extinction spectrometer has been established, the uncertainty is determined to be less than 3% by laboratory-generated standard particles with different sizes and concentrations to verify the reliability of the system.(2) Using the established aerosol extinction spectrometer, the performance indices of the instrument were also characterized: the ring-down time of filtered background air is 51.26 μs, has a detection limit of aerosol extinction as low as 10-7m-1 level, and the response time is less than 2 min. It was demonstrated that the performance of this home-made aerosol extinction spectrometer introduced in this thesis was high performance and it could meet requirements of most atmospheric aerosol studies. This instrument will play important roles in areas associated with aerosol optical properties environmental monitoring.(3) Combining the statistical results of meteorological factors, the aerosol extinction characteristics and its diurnal pattern around yangcheng lake, kunshan, was analyzed in detail through a long-term observation. Observation results show that the the reasons are due to the great influence of the surrounding heavily polluted areas and the meteorological conditions.(4) To understand the influence of relative humidity to aerosol extinction coefficient, two same instruments were employed to determine the atmospheric aerosol extinction coefficient in different relative humidity. The hydrophilic properties of atmospheric aerosol in the monitoring site was also studied preliminarily by using hydrophilic parameters gamma.