Development of LIF instrument for Measuring Tropospheric Hydorxyl Radicals and Verification of Photochemical Theory

1996 Fiscal Year Final Research Report Summary

• Project/Area Number: 06403031
• Research Category: Grant-in-Aid for Scientific Research (A)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Environmental dynamic analysis
• Research Institution: RESEARCH CENTER FOR ADVANCED SCIENCE AND TECHNOLOGY,THE UNIVERSITY OF TOKY
• Principal Investigator: AKIMOTO Hajime THE UNIVERSITY OF TOKYO,RESEARCH CENTER FOR ADVANCED SCIENCE AND TECHNOLOGY,PROFESSOR, 先端科学技術研究センター, 教授 (50101043)
• Co-Investigator(Kenkyū-buntansha): HIROKAWA Jun THE UNIVERSITY OF TOKYO,RESEARCH CENTER FOR ADVANCED SCIENCE AND TECHNOLOGY,RESE, 先端科学技術研究センター, 助手 (20262115) ; KAJII Yoshizumi THE UNIVERSITY OF TOKYO,RESEARCH CENTER FOR ADVANCED SCIENCE AND TECHNOLOGY,RESE, 先端科学技術研究センター, 助教授 (40211156)
• Project Period (FY): 1994 – 1996
• Keywords: OH radical / troposphere / optical absorption / Low pressure LIF / Interference of O_3 / Photon Counting / Detection Limit / Sensitivity

Research Abstract

We designed and constructed vacuum chamber and vacuum system for measuring ambient OH radical concentration. To detect OH radical free from O_3 chemical interference the Low Pressure Laser Induced Fluorescence technique was employed. The lasers system of tunable dye laser pumped by 2rd harmonic of pulsed Nd : YAG laser which was pumped by diode laser was constructed. The out-put of dye laser was doubled to excite OH radical into single ro-vibronic level of the first doublet excited state (A^2SIGMA^+v''=0). LIF singnals of OH radicals were collected by lens system and detected by MCP gated PMT after interference fillter of 308 nm. Photon counting technique was employed to improve S/N ratio. To determine the absolute concentration of OH radicals, two techniques were employed for calbration for the LIF instrument. One is chemical titration method to control radical concentrations ; the reaction H + NO_2*OH + NO was used. Using this reaction and assuming that this reaction is fast enough and chemical loss of OH radical is negligible, concentration of OH raical was controled. The other method employed was optical absorption technique. Multi-pass absorption (base path=1 m ; 100 times) and VUV photolysis of water vapor were used to calbrate the instrument. From these independent techniques, sensitivity of the instrument was determined to be 5 * 10^<-9> and 9 * 10^<-9>/cps mW^<-1>/ (OH cm^<-3>). This good agreement indicates our system has enough precision. Limit of detection (LOD) was estimated to be 7 * 10^8 radicals cm^<-3> under present condition. It is found that this instrument has enough potential for measuring ambient HO_2 radical.