Measurement of tropospheric HO_(2) radical using fluorescence assay by gas expansion with low interferences

摘要

An instrument to detect atmospheric HO_(2) radicals using fluorescence assay by gas expansion(FAGE)technique has been developed.HO_(2) is measured by reaction with NO to form OH and subsequent detection of OH by laser-induced fluorescence at low pressure.The system performance has been improved by optimizing the expansion distance and pressure,the influence factors of HO_(2) conversion efficiency are also studied.The interferences of RO_(2) radicals were investigated by determining the conversion efficiency of RO_(2) to OH during the measurement of HO_(2).The dependence of the conversion of HO_(2) on NO concentration was investigated,and low HO_(2) conversion efficiency was selected to realize the ambient HO_(2) measurement,where the conversion efficiency of RO_(2) derived by propane,ethene,isoprene and methanol to OH has been reduced to less than 6%in the atmosphere.Furthermore,no significant interferences from PM_(2.5) and NO were found in the ambient HO_(2) measurement.The detection limits for HO_(2)(S/N=2)are estimated to 4.8×10^5 cm^-3 and 1.1×10^6 cm^-3(ρHO_(2)=20%)under night and noon conditions,with 60 sec signal integration time.The instrument was successfully deployed during STORM-2018 field campaign at Shenzhen graduate school of Peking University.The concentration of atmospheric HOx radical and the good correlation of OH with j(O1D)was obtained here.The diurnal variation of HOx concentration shows that the OH maximum concentration of those days is about 5.3×10^6 cm^-3 appearing around 12:00,while the HO_(2) maximum concentration is about 4.2×10^8 cm^-3 appearing around 13:30.