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

对流层羟基自由基测量LIF仪的研制及光化学理论验证

• 批准号: 06403031
• 负责人: AKIMOTO Hajime
• 金额: $ 18.37万
• 依托单位: RESEARCH CENTER FOR ADVANCED SCIENCE AND TECHNOLOGY,THE UNIVERSITY OF TOKY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (A)
• 财政年份: 1994
• 资助国家: 日本
• 起止时间: 1994 至 1996
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-06403031/
• 关键词: OH radical; troposphere; optical absorption; Low pressure LIF; Interference of O_3; Photon Counting; Detection Limit; Sensitivity; OHラジカル; レーザー誘起蛍光法; 長光路レーザー吸収法; 対流圏

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.

我们设计并建造了用于测量环境 OH 自由基浓度的真空室和真空系统。为了检测不受 O_3 化学干扰的 OH 自由基，采用了低压激光诱导荧光技术。构建了二极管激光器泵浦的脉冲Nd:YAG激光器二次谐波泵浦的可调谐染料激光器激光系统。染料激光的输出加倍，将 OH 自由基激发到第一双激发态的单振动电子能级 (A^2SIGMA^+v''=0)。通过透镜系统收集OH自由基的LIF信号，并在308 nm干涉滤波器后通过MCP门控PMT检测。采用光子计数技术来提高信噪比。为了确定 OH 自由基的绝对浓度，采用了两种技术来校准 LIF 仪器。一是化学滴定法控制自由基浓度；使用反应H + NO_2*OH + NO。使用该反应并假设该反应足够快并且OH自由基的化学损失可以忽略不计，OH自由基的浓度受到控制。采用的另一种方法是光吸收技术。采用多程吸收（基本路径=1 m；100次）和水蒸气的VUV光解来校准仪器。根据这些独立的技术，仪器的灵敏度被确定为5*10^-9和9*10^-9/cps mW^-1/(OH cm^-3)。这种良好的一致性表明我们的系统具有足够的精度。在目前的条件下，检测限(LOD)估计为7*10^8根cm^-3。发现该仪器具有足够的潜力测量环境HO_2自由基。