Atmospheric Peroxy Radical Measurement And Field Observation Based On Chemical Amplification

Peroxy radicals(RO2*=RO2+HO2)are key species in atmosphere.They are produced during the oxidation of volatile organic compounds(VOCs)and are involved in the formation of photochemical pollutants such as ozone(O3)and secondary organic aerosols(SOA).Consequently,knowledge about the spatial distribution and concentration of HO2 and RO2 is essential to test the present understanding of tropospheric chemistry.However,measuring peroxy radicals is particularly difficult due to their reactive nature and their low ambient concentrations,which require highly sensitive techniques.The peroxy radical chemical amplifier(PERCA)is an indirect measurement method,which measures the sum of peroxy radicals continuously with high sensitivity and low limit detection.In this paper,a chemical amplified peroxy radical instrument was used to measure the peroxy radical in situ.The main contents can be generalized as follows:1.Based on the Nafion drying tube as a chemical reaction chamber,a dual-channel chemically amplification broadband-cavity enhanced spectroscopy system for the measurement of the peroxy radicals was developed.The experimental chain length(CL)for PERCA was 100 ± 10.And the dual-channel PERCA system can effectively reduce the effect of high relative humidity on CL.2.A single-channel BBCEAS-PERCA system was established.The chemical amplification peroxy radical measurement system and the peroxy radical calibration system were optimized,the measurement device is more integrated and lower cost,the volume and mass are further reduced,more convenient for field observation.3.Different peroxy radical calibration sources were established.High-purity N2carrying water was used to generate water vapor,which was photolyzed and reacted with O2 to generate HO2.The method can effectively avoid the interference of O3,and the calibration process was fast,simple,and free of other interference.For the source of organic peroxy radicals,high-purity N2-loaded acetone was used to photolyze and react with O2 to generate organic peroxy radicals.And the chemical chain length of the peroxy radical source from H2O2 pyrolysis,H2O photolysis,and acetone photolysis is the same as the reactant gas(NO,CO)and relative humidity.4.The measurement device based on chemical amplification-broadband cavity enhanced spectroscopy was applied to the atmospheric field observation.Peroxy radicals in Heshan,Hefei,Nyingchi,and Huaibei were measured respectively.The peroxy radicals have an obvious diurnal variation,which was low at night and high during the day,reaching a peak at noon.In 2019 autumn,at Heshan site,the peak concentration of RO2*was 43.56pptv;in 2020 summer,at Hefei site,the RO2*peak was 43.8pptv;in 2021 spring,at Nyingchi site,the daily variation of RO2*was similar to the plain area,the peak concentration of RO2*was 62.23pptv;in 2021 summer,at Huaibei site,the RO2*peak was 75pptv.5.Using the observed peroxy radical,combined with the measurement of NO,the photochemical ozone production rate can be determined with real-time.Based on the measured peroxy radical,the ozone production rate in summer at Hefei site and Huaibei site were analyzed.The peak ozone production rate in the western suburbs of Hefei in summer 2020 was 10.6ppbv/h;in summer 2021,the peak ozone production rate in Huaibei was 14ppbv/h.The characteristics of the generation and elimination of ozone pollution in Huaibei area were discussed,and the results showed that photochemical generation of ozone increased significantly,which made an important contribution to the locally high concentration of O3.