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摘要

OH自由基是大气中最重要的氧化剂, 准确测量对流层OH自由基的浓度是厘清我国二次污染形成机理的关键. 本文介绍了一种基于同步光解的OH自由基便携式标定方法, 使用汞灯的185 nm线辐射处于层流状态下的具有一定水汽浓度的合成空气, 光解HO ₂和O ₂定量产生确定浓度的OH, HO ₂自由基和O ₃. 开展了臭氧浓度及廓线分布因子 P和氧气吸收截面等影响因素的准确测量, 降低该标定方法的不确定度. 进一步构建便携式标定装置, 建立应用于实际外场标定的OH自由基浓度快速获取方法. 开展基于激光诱导荧光技术OH自由基(LIF-OH)探测系统的准确标定测试, 准确产生3×10 ⁸—2.8×10 ⁹cm ^–3浓度的OH自由基, LIF-OH探测系统的荧光信号与自由基浓度具有非常好的相关性. 在综合外场观测(STORM)的应用中该标定装置的不确定度为13.0%, 具有良好的稳定性和准确性, 可以用于复杂外场环境下LIF-OH系统的快速标定.

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Abstract

OH radical is the most important oxidant in the atmosphere, and controls the tropospheric concentration of tropospheric trace gases such as CO, SO ₂, NO ₂, CH ₄and other volatile organic compounds. Accurate measurement of the concentration of OH radical in troposphere is the key to clarifying the formation mechanism of secondary pollution in China. The laser-induced fluorescence (LIF) technique is widely used in tropospheric OH radical field observation due to its high sensitivity, high selectivity, and small interference. However, the LIF technique is not an absolute measurement technology. In recent years, OH radical measurements and simulations in many field observations show that the improvement of accuracy of calibration is a way to reduce the differences. Currently, the common calibration methods are ozone-alkene method and water photolysis method. Further improving the accuracy of calibration is a key factor to ensure the accurate measurement of OH radicals. In this paper, a portable calibration method of OH radicals based on simultaneous photolysis is introduced. The synthetic air with a certain water vapor concentration is irradiated in laminar flow by 185 nm light of mercury lamp, and the photolysis of water vapor and O ₂produce OH, HO ₂radicals and O ₃. The concentration of OH radicals is calculated by oxygen concentration, water vapor concentration, ozone concentration, oxygen absorption cross section and water vapor absorption cross section. The water vapor is measured by a high-precision temperature and humidity probe, and the systematic error of the probe is corrected by 911-0016 ammonia (NH ₃, H ₂O) analyzer. As the ozone concentration is only 0.5－1 ppb in the calibration, the commercial ozone analyzer cannot meet the requirement for the measurement. A high-precision ozone analyzer O ₃-CRDS based on cavity-ring-down spectrocopy is built to achieve the detection limit of 15 ppt (1σ). Using the O ₃-CRDS analyzer, the concentration distribution coefficient of ozone in laminar flow along the radial direction of the flow tube ( P= 1.9) is measured. Because the absorption cross section of oxygen at 185 nm is seriously affected by oxygen column concentration and the characteristics of mercury lamp, the oxygen absorption cross section is remeasured based on Lambert’s law, which is

$ \sigma_{\rm O_2} $

= (1.25 ± 0.08)×10 ^–20cm ². The portable calibration device is established by establishing the corresponding relationship between ozone concentration and light intensity. By changing the concentration of water vapor in the flow tube, the OH radicals with concentrations in a range of 3×10 ⁸－2.8×10 ⁹cm ^–3are produced, which are used to calibrate the atmospheric OH radical measurement instrument based on LIF technique. The fluorescence signal has a good correlation with the concentration of OH. The calibration device of OH radical is used to calibrate the LIF system during “a comprehensive study of the ozone formation mechanism in Shenzhen” (STORM) field observation in Autumn 2018. The calibration results under the field condition show that the calibration uncertainty of the calibration device for LIF instrument is 13.0%, which has good stability and accuracy.

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作者及机构信息

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通信作者:胡仁志,rzhu@aiofm.ac.cn; 谢品华,phxie@aiofm.ac.cn;

基金项目:国家级-国家重点研发计划(2017YFC0209401)

Authors and contacts

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Corresponding author:Hu Ren-Zhi,rzhu@aiofm.ac.cn; Xie Pin-Hua,phxie@aiofm.ac.cn;

文章全文: translate this paragraph

参考文献

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施引文献

下载: 全尺寸图片幻灯片

误差源	不确定度	来源
臭氧分布系数P	6.0%	测量
臭氧灵敏度Q_v	2.9%	测量
PD光强I'	1.0%	测量
水汽浓度[H₂O]	2.0%	测量
氧气吸收截面$ \sigma _{\rm O_2} $	7.0%	测量
水汽吸收截面$ {\sigma _{{{\rm{H}}_2}{\rm{O}}}} $	3.0%	引用
标定装置产生OH自由基误差	10.4%	计算

下载: 导出CSV

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