Development And Application Of A Dual-channel Chemically Amplification Broadband-cavity Enhanced Spectroscopy

Peroxy radicals(RO2 and HO2)are key intermediates in the atmospheric degradation oxidation of volatile organic compounds,which play a role between degradation of primary pollutant and formation of secondary pollutant.Peroxy radicals can convert NO into NO2,and then produces O3 by photolysis of NO2,which causes the accumulation of O3 in atmosphere.At the time,the low-volatile organic compounds generated by the further reactions of peroxy radical aer important precursors of atmospheric fine particle.It is of great signif-icance to accurately measure the concentration of RO2 for understanding the atmospheric chemical reaction of VOCs and the formation mechanism of SOA.However,due to the high activity,low concentration,short life of peroxy radicals,and the complex atmospheric environment,it is always difficult to accurately measure them.In order to obtain the concentration of peroxyl radicals in the atmosphere,we have carried out the following work based on previous studies:1.We have developed a dual-channel chemically amplification broadband-cavity enhanced spectroscopy system for the measurement of the concentration of peroxy radicals.In order to determine the key parameter in PERCA-chemical chain length,we developed a hydrogen peroxide pyrolysis system to obtain stable HO2,used for calibration of chemical chain length,and optimized the relevant parameters to obtain the optimal chain length(about 92±11).Through experimental research,it is found that the dual-channel PERCA system can effectively avoid the interference of NO2 and O3 in atmosphere.2.In order to eliminate the interference of relative humidity on the chemical chain length,we have developed a new Nafion dryer based dual-channel PERCA system for accurate and sensitive measurement of ambient peroxy radicals.The Nafion dryer muted the influence of humidity on the CL.At 48%inlet RH,the value of CLwet(48%RH)/CLdry(5%RH)was?0.88.However,it bears a trade-off between inlet radical losses and moisture removal efficiency under high ambient RH conditions.3.To make the PERCA instrument well suited for most ambient conditions(with low inlet loss and low CL loss under high RHinlet condition),we made a further improvement of our previous system,by using Nafion Dryer as Amplification Reactor.A linear relationship between CL and RHinlet up to 87%RH was observed.Low loss of the CL under high RHinlet(about 10%reduction at 87%RH)was achieved,which made the system can largely remove water vapor interference and validated under most ambient conditions.4.We have successfully applied the dual-channel PERCA system to measure the concentration of peroxyl radicals in the actual atmosphere and in experiment in smog chamber In smog chamber,experiment of a-pinene ozonolysis was carried out,measured the change of the concentration peroxygen radical during the experiment by the dual-channel PERCA system.Combined with the chemical mechanism of MCM,the formation route of main RO2 and the formation process of main secondary organic aerosol during the ozonation of a-pinene were analyzed.At the site of the Guangzhou Institute of Geochemistry,we conducted continuous observation of peroxyl radicals,obtained the real-time concentration of peroxyl radicals in the region,and the relusts was similar to previous measurements.