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Characterization of a chemical modulation reactor (CMR) for the measurement of atmospheric concentrations of hydroxyl radicals with a laser-induced fluorescence instrument
Atmospheric Measurement Techniques ( IF 3.8 ) Pub Date : 2020-09-14 , DOI: 10.5194/amt-2020-359 Changmin Cho , Andreas Hofzumahaus , Hendrik Fuchs , Hans-Peter Dorn , Marvin Glowania , Frank Holland , Franz Rohrer , Vaishali Vardhan , Astrid Kiendler-Scharr , Andreas Wahner , Anna Novelli
Atmospheric Measurement Techniques ( IF 3.8 ) Pub Date : 2020-09-14 , DOI: 10.5194/amt-2020-359 Changmin Cho , Andreas Hofzumahaus , Hendrik Fuchs , Hans-Peter Dorn , Marvin Glowania , Frank Holland , Franz Rohrer , Vaishali Vardhan , Astrid Kiendler-Scharr , Andreas Wahner , Anna Novelli
Abstract. Precise and accurate hydroxyl radical (OH) measurements are essential to investigate how trace gases are oxidized and transformed in the troposphere and how secondary pollutants like ozone (O3) are formed. Laser induced fluorescence (LIF) is a widely used technique for the measurement of ambient OH radicals and was used for the majority of field campaigns and chamber experiments. Recently, most LIF instruments in use for atmospheric measurements of OH radicals introduced chemical modulation to separate the ambient OH radical concentration from possible interferences by chemically removing ambient OH radicals before they enter the detection cell. In this study, we describe the application, characterization, and validation of a chemical modulation reactor (CMR) applied to the Forschungszentrum Jülich LIF (FZJ-LIF) instrument in use at the atmospheric simulation chamber SAPHIR. Besides dedicated experiments in synthetic air, the new technique was extensively tested during the year-round Jülich Atmospheric Chemistry Project (JULIAC) campaign, in which ambient air was continuously flowed into the SAPHIR chamber. It allowed performing OH measurement comparisons with Differential Optical Absorption Spectroscopy (DOAS) and investigation of interferences in a large variety of chemical and meteorological conditions. A good agreement was obtained in the LIF DOAS intercomparison within instrumental accuracies (18 % for LIF, 6.5 % for DOAS) which confirms that the new chemical modulation system of the FZJ-LIF instrument is suitable for measurement of interference-free OH concentrations. Known interferences from O3 + H2O and the nitrate radical (NO3) were quantified with the CMR in synthetic air in the chamber and found to be 3.0 × 105 cm-3 and 0.6 × 105 cm-3, respectively, for typical ambient air condition (O3 = 50 ppbv, H2O = 1 %, NO3 = 10 pptv). The interferences measured in ambient air during the JULIAC campaign in summer season had the median diurnal variation of the interference with a maximum daytime value of 0.9 × 106 cm-3 and a minimum nighttime value of 0.4 × 106 cm-3. The highest interference of 2 × 106 cm-3 occurred in a heat wave from 22–29 August, when the air temperature and ozone increased to 40 °C and 100 ppbv, respectively. All observed interferences could be fully explained by the known O3 + H2O interference, which is routinely corrected in FZJ-LIF measurements when no chemical modulation is applied. No evidence for unexplained interference was found during the JULIAC campaign. A kinetic chemical model of the chemical modulation reactor was developed and applied to estimate the possible perturbation of the OH transmission and scavenging efficiency by reactive atmospheric trace gases. These can remove OH by gas phase reactions in the reactor, or produce OH by non-photolytical reactions, most importantly by the reaction of ambient HO2 with NO. The interfering processes become relevant at high atmospheric OH reactivities. For the conditions of the JULIAC campaign with OH reactivities below 20 s-1, the influence on the determination of ambient OH concentrations was small (on average: 2 %). However, in environments with high OH reactivities, such as in a rain forest or megacity, the expected perturbation in the currently used chemical modulation reactor could be large (more than a factor of 2) and would need careful analysis and correction. This implies that chemical modulation, which was developed to eliminate interferences in ambient OH measurements, itself can be subject to interferences that depend on ambient atmospheric conditions.
中文翻译:
化学调制反应器(CMR)的表征,用于使用激光诱导的荧光仪器测量大气中的羟基自由基浓度
摘要。精确而准确的羟基自由基(OH)测量对于研究痕量气体如何在对流层中被氧化和转化以及诸如臭氧(O 3) 形成。激光诱导荧光(LIF)是一种广泛用于测量环境OH自由基的技术,并用于大多数野战活动和室内试验。最近,大多数用于大气中的OH自由基测量的LIF仪器引入了化学调制,通过在环境OH自由基进入检测池之前进行化学去除,将环境OH自由基浓度与可能的干扰分离。在这项研究中,我们描述了应用于大气模拟室SAPHIR的ForschungszentrumJülichLIF(FZJ-LIF)仪器的化学调制反应器(CMR)的应用,表征和验证。除了在合成空气中进行专门的实验外,在全年的Jülich大气化学项目(JULIAC)活动中,这项新技术得到了广泛的测试,在该活动中,环境空气不断流入SAPHIR室。它允许使用差分光学吸收光谱(DOAS)进行OH测量比较,并研究各种化学和气象条件下的干扰。在仪器精度范围内的LIF DOAS比较中获得了很好的协议(LIF为18%,DOAS为6.5%),这证实了FZJ-LIF仪器的新化学调制系统适用于测量无干扰的OH浓度。来自O的已知干扰 它允许使用差分光学吸收光谱法(DOAS)进行OH测量比较,并研究各种化学和气象条件下的干扰。在仪器精度范围内的LIF DOAS比较中获得了很好的协议(LIF为18%,DOAS为6.5%),这证实了FZJ-LIF仪器的新化学调制系统适用于测量无干扰的OH浓度。来自O的已知干扰 它允许使用差分光学吸收光谱(DOAS)进行OH测量比较,并研究各种化学和气象条件下的干扰。在仪器精度范围内的LIF DOAS比较中获得了很好的协议(LIF为18%,DOAS为6.5%),这证实了FZJ-LIF仪器的新化学调制系统适用于测量无干扰的OH浓度。来自O的已知干扰 DOAS为5%),这表明FZJ-LIF仪器的新化学调制系统适用于测量无干扰的OH浓度。来自O的已知干扰 DOAS为5%),这表明FZJ-LIF仪器的新化学调制系统适用于测量无干扰的OH浓度。来自O的已知干扰在室内合成空气中使用CMR对3 + H 2 O和硝酸根(NO 3)进行定量,对于典型的环境空气,分别为3.0×10 5 cm -3和0.6×10 5 cm -3。条件(O 3 = 50 ppbv,H 2 O = 1%,NO 3 = 10 pptv)。夏季JULIAC运动期间在环境空气中测得的干扰具有中值昼夜变化,白天的最大值为0.9×10 6 cm -3,夜间的最小值为0.4×10 6 cm -3。在8月22日至29日的热浪中,最高干扰2×10 6 cm -3发生,当时空气温度和臭氧分别升高至40°C和100 ppbv。可以通过已知的O 3 + H 2充分解释所有观察到的干扰O干扰,如果不进行化学调制,则可以在FZJ-LIF测量中常规纠正。在JULIAC运动期间,没有发现无法解释的干扰的证据。建立了化学调制反应器的动力学化学模型,并将其应用于估算反应性大气微量气体对OH传输和清除效率的可能扰动。这些可以通过反应器中的气相反应除去OH,或通过非光解反应,最重要的是通过环境HO 2与NO的反应产生OH 。干扰过程在高的大气OH反应性下变得很重要。对于JULIAC运动的条件,OH反应性低于20 s -1,对环境OH浓度测定的影响很小(平均:2%)。但是,在具有高OH反应性的环境中,例如在雨林或特大城市中,当前使用的化学调制反应器中的预期扰动可能很大(超过2倍),需要仔细分析和校正。这意味着为消除环境OH测量中的干扰而开发的化学调制本身可能会受到取决于周围大气条件的干扰。
更新日期:2020-09-14
中文翻译:
化学调制反应器(CMR)的表征,用于使用激光诱导的荧光仪器测量大气中的羟基自由基浓度
摘要。精确而准确的羟基自由基(OH)测量对于研究痕量气体如何在对流层中被氧化和转化以及诸如臭氧(O 3) 形成。激光诱导荧光(LIF)是一种广泛用于测量环境OH自由基的技术,并用于大多数野战活动和室内试验。最近,大多数用于大气中的OH自由基测量的LIF仪器引入了化学调制,通过在环境OH自由基进入检测池之前进行化学去除,将环境OH自由基浓度与可能的干扰分离。在这项研究中,我们描述了应用于大气模拟室SAPHIR的ForschungszentrumJülichLIF(FZJ-LIF)仪器的化学调制反应器(CMR)的应用,表征和验证。除了在合成空气中进行专门的实验外,在全年的Jülich大气化学项目(JULIAC)活动中,这项新技术得到了广泛的测试,在该活动中,环境空气不断流入SAPHIR室。它允许使用差分光学吸收光谱(DOAS)进行OH测量比较,并研究各种化学和气象条件下的干扰。在仪器精度范围内的LIF DOAS比较中获得了很好的协议(LIF为18%,DOAS为6.5%),这证实了FZJ-LIF仪器的新化学调制系统适用于测量无干扰的OH浓度。来自O的已知干扰 它允许使用差分光学吸收光谱法(DOAS)进行OH测量比较,并研究各种化学和气象条件下的干扰。在仪器精度范围内的LIF DOAS比较中获得了很好的协议(LIF为18%,DOAS为6.5%),这证实了FZJ-LIF仪器的新化学调制系统适用于测量无干扰的OH浓度。来自O的已知干扰 它允许使用差分光学吸收光谱(DOAS)进行OH测量比较,并研究各种化学和气象条件下的干扰。在仪器精度范围内的LIF DOAS比较中获得了很好的协议(LIF为18%,DOAS为6.5%),这证实了FZJ-LIF仪器的新化学调制系统适用于测量无干扰的OH浓度。来自O的已知干扰 DOAS为5%),这表明FZJ-LIF仪器的新化学调制系统适用于测量无干扰的OH浓度。来自O的已知干扰 DOAS为5%),这表明FZJ-LIF仪器的新化学调制系统适用于测量无干扰的OH浓度。来自O的已知干扰在室内合成空气中使用CMR对3 + H 2 O和硝酸根(NO 3)进行定量,对于典型的环境空气,分别为3.0×10 5 cm -3和0.6×10 5 cm -3。条件(O 3 = 50 ppbv,H 2 O = 1%,NO 3 = 10 pptv)。夏季JULIAC运动期间在环境空气中测得的干扰具有中值昼夜变化,白天的最大值为0.9×10 6 cm -3,夜间的最小值为0.4×10 6 cm -3。在8月22日至29日的热浪中,最高干扰2×10 6 cm -3发生,当时空气温度和臭氧分别升高至40°C和100 ppbv。可以通过已知的O 3 + H 2充分解释所有观察到的干扰O干扰,如果不进行化学调制,则可以在FZJ-LIF测量中常规纠正。在JULIAC运动期间,没有发现无法解释的干扰的证据。建立了化学调制反应器的动力学化学模型,并将其应用于估算反应性大气微量气体对OH传输和清除效率的可能扰动。这些可以通过反应器中的气相反应除去OH,或通过非光解反应,最重要的是通过环境HO 2与NO的反应产生OH 。干扰过程在高的大气OH反应性下变得很重要。对于JULIAC运动的条件,OH反应性低于20 s -1,对环境OH浓度测定的影响很小(平均:2%)。但是,在具有高OH反应性的环境中,例如在雨林或特大城市中,当前使用的化学调制反应器中的预期扰动可能很大(超过2倍),需要仔细分析和校正。这意味着为消除环境OH测量中的干扰而开发的化学调制本身可能会受到取决于周围大气条件的干扰。