Peroxy Radicals Measurements By Using Chemical Amplification Cavity Enhanced Spectroscopy

Atmospheric peroxy radical, with strong oxidizing and high reactivity, is important antioxidants in atmospheric environment. The peroxy radical study is important for an understanding of atmospheric oxidizing capacity and the generate of photochemical ozone and secondary organic aerosol, and its study of measurements has become the hot spot of domestic and international research.In this study, an instrument for real-time online measurement of peroxy radical by chemical amplification has been developed, named as PERCA-CEAS. It firstly combined chemical amplification and broadband cavity enhanced absorption spectroscopy to the real-time, online, continuous measurement of peroxy radical. The main contents can be generalized as follows:(1) Based on the principle of chemical amplification method, we set up a chemical amplification gas circuit system that could realize the chain reaction of peroxy radical, which low concentration, difficult to measured peroxy radicals can be convert into high concentration, easy to measured NO2.(2) We designed and set up a system of HO2 radical standard source. The source can generated continued, steady HO2 radical based the principle of the thermal decomposition of hydrogen peroxide in 600℃。The source used bubbling method, zero air carrier and it can be used the calibration of chain length.(3) Carring out the research of the measurement of NO2 using broadband cavity enhanced absorption spectroscopy. We describes the development and measurement principle of Cavity enhanced absorption spectroscopy, and introduced the design and establishment of the CEAS. The CEAS selected a bule LED as light source which central wavelength is 460nm. The LED and temperature sesor (AD590) were installed on a thermal conductivity piece, current and temperature is controlled by a high precision power control, to ensure the stability of light source output light intensity. The Optical cavity is composed of a quartz tube and two high reflectivity mirrors at the ends of the cavity, which the quartz tube is 85 cm length and 25 mm inner diameter. The high reflectivity mirrors (LGR,1 m in diameter, curvature radius of 1 m), whose wavelength range of high reflectivity area is 415 nm to 465 nm. The two high reflectivity mirrors were flushing by high purity nitrogen to protect the mirrors against pollution and corrosion. The optical cavity fixed within the framework of stainless steel, can be very good to keep the stability of the instrument. And we also described the calibration of the reflectivity and the effective length of CEAS.(4) We described the chain length calibration results of chemical amplification method, and gives the analysis and optimization for the influencing factor of chain length that concluded that in NO concentration of 7.7 ppm, CO concentration was 8.5%, under the condition of reaction time of 1 s, chain length can reach up to 91±11, the uncertainty was 12%. The detection limit of the PERCA-CEAS system was 2.08 pptv when the sampling time is 9s.