Application of pulse cavity ring-down spectroscopy technique for aerosol extinction measurement

摘要

In recent years, there has been a rapid rise in the use of pulse cavity ring-down spectroscopy to determine the optical properties of atmospheric aerosols. In the present work ,we describes the design and performance of a CRDS system for measuring extinction coefficients of atmospheric aerosols. CRDS based methods can achieve impressive sensitivity owing to the long effective path lengths involved. More importantly, the method is not affected by laser intensity fluctuations since the rate of attenuation of light is the measured variable rather than absolute irradiance. The extinction coefficient is a function of the cavity ring-down time. Determining an accurate decay time is critical to precise measurements of the extinction coefficients. The average and standard deviation of the decay time (τ_0 is measured 6 hours ,cavity filled only with dry nitrogen) is about 42.21 μs and 0.16μs, respectively. Moreover, a minimum detectable aerosol extinction coefficient of 0.41Mm~(-1) is achieved. Allan deviation plots for the value of tτ_0 measurements, close to a flicker noise. The minima(～5.8×10~(-4)μs) in the Allan plots indicate the optimum average time(～60s) for optimum detection performance. To test the performance of the CRDS system, we monitored the optical properties of ambient aerosols on the campus of the Zhejiang Normal University from January 3rd to January 7th, 2014. During this period, the average value of the extinction coefficient is 816.8Mm~(-1), a maximum value more than 1800 Mm~(-1), and a minimum aerosol extinction coefficient of 119.27 Mm~(-1) is detected.