Application Research Of Phase Shift Spectroscopy Technology Measurements Of Aerosol Extinction Cofficient

The atmospheric aerosols play an important role in the radiation budget of Earth-atmosphere system and have significant radiative effects to the human health, the atmospheric climate, air quality and ecological changes. Atmospheric aerosols have been recognized as one of the largest contributors in increasing atmospheric greenhouse effect. Aerosol radiative forcing remains one of the largest uncertainties in quantifying the role that aerosol play in the Earth’s radiative budget. However, aerosol radiative forcing has important scientific significance on the analysis of atmospheric radiation balance, chemical process and climate change. Therefore, to better quantify the influence of atmospheric particles on radiative forcing, the measurement of aerosol radiative forcing has always been a research hot spot.With the in-depth development of the aerosol radiative forcing effect on the climate, the precise measurement of aerosol optical parameters is becoming particularly important. As the key in the study of aerosol climate model, aerosol optical parameters has great significance for improving the prediction precision of climate models. For example, aerosol extinction coefficient can be used as a measure reflecting the atmospheric visibility, etc. At the same time, aerosol extinction coefficient has close radiations with the aerosol absorption, scattering and single albedo. So an accurate measurement of aerosol extinction characteristics is of great scientific significance in understanding the aerosol radiative forcing.At present, there are three kinds of technology of aerosol extinction characteristics measurement, such as Lidar technology, sun photometer technique and pulse ring-down spectroscopy technique. A variety of optical properties of aerosol parameters can be determined at the same time, through the use of laser radar technology. However, this method costs high, not suitable for routine measurement, large volume and background interference etc. Using photometer measurement extinction coefficient, simple operation and portable system. Unfortunately, this method cannot normal measurement in cloudy or rainy days, and the measurement precision is low. Monitoring optical properties of aerosols with cavity ring-down spectroscopy technology, accurate, in situ measurements of optical absorption and extinction, but the cost of the laser is thousands of times the cost of LED light source. In order to solve the existing problems of the measuring methods, a detection method based on Phase shift spectroscopy technique is presented in this paper.Phase shift spectroscopy technique based methods can achieve impressive sensitivity owing to the long effective path lengths involved. More importantly, the technology using the light source is cheap.Phase shift spectroscopy has more prominent advantages in the practical application process, and the application is very extensive, such as measurement reflectivity, trace gas concentration, measurement of aerosol extinction coefficient. Phase shift spectroscopy uses a square wave modulated light emitting diode (LED) as a light source and measures the change in the phase shift of the distorted waveform of the modulated light leaving a highly reflective optical cell. The aerosol extinction aext is derived from such change in the phase shift.In this article, first using the theory of first-order sensing, optical cavity as a first-order system, this paper derived the Pulse Cavity ring-down spectroscopy technology and Phase shift spectroscopy technology theory. Theoretical simulation analysis of the extinction coefficient measurement technique index. We describe the design and function of a simpler Phase Shift system. The measurement system mainly includes:LED, optical cavity, a photomultiplier tube and a lock-in amplifier. First of all, the system used for measuring the cavity reflectivity. Secondly, the system used for measuring the optical cavity loss qualitative, simultaneously measuring the stability of the system. Through the Allan analysis of variance, phase shift measurement system detection limit the size of the extinction coefficient. Finally, phase shift system used for measuring atmospheric aerosol extinction coefficient in Jinhua area, and analysis of measurement results. In last, we summarize the full text, and put forward the prospect of future work.