Comparison of OH reactivity measurements in the atmospheric simulation chamber SAPHIR
Comparison of OH reactivity measurements in the atmospheric simulation chamber SAPHIR
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DOI：
10.5194/amt-10-4023-2017
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发表时间：
2017-10-27
影响因子：
3.8
通讯作者：
Wahner, Andreas
中科院分区：
文献类型：
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作者：
Fuchs, Hendrik;Novelli, Anna;Wahner, Andreas
羟基（OH）自由基反应性（k（OH））已经用不同的测量技术测量了18年。为了比较现场部署的仪器的性能，2015年10月和2016年4月在Forschungszentrum Julich的大气模拟室SAPHIR中进行了两次活动。选择的化学条件要么代表大气，要么测试仪器的潜在局限性。目前用于大气测量的所有类型的仪器都用于这两次活动中的一次。这些活动的结果表明，所有仪器都可以准确地测量各种大气相关化学条件（例如水蒸气，氮氧化物，各种有机化合物）的OH反应性。测量的精确度（在30 s至几分钟的时间分辨率下，检测限< 1 s（-1））对于直接检测羟基自由基的仪器较高，而间接比较反应性方法（CRM）在10至15 min的时间分辨率下具有2 s（-1）的较高检测限。例如一氧化碳（CO）、水蒸气或一氧化氮（NO）的浓度。在进一步的实验中，将有机反应物的混合物注入腔室以模拟城市和森林环境。总体而言，结果表明，该仪器能够测量在CO，烷烃，烯烃和芳香族化合物的存在下的OH反应性。特氟龙入口管线的传输效率可能会在某些仪器中对低挥发性有机化合物的测量中引入系统误差。与其他仪器相比，CRM仪器在数据中表现出更大的分散性。在萜烯和含氧有机化合物（OH反应物的混合比高达10 ppbv）的存在下，通过CRM仪器观察到与参考测量或计算的反应性的最大差异。在这些实验中，只有一小部分的反应性被检测到。CRM测量的准确性很可能受到需要应用的校正的限制，以解释例如与伪一阶条件、氮氧化物或水蒸气的偏差对测量的已知影响。不同的CRM工具所使用的得出这些校正值的方法各不相同。用流管仪器结合化学电离质谱法（CIMS）直接检测OH进行的测量在高反应性和高NO浓度的情况下显示出局限性，但在低反应性（< 15 s（-1））和低NO（< 5 ppbv）条件下是准确的。
Hydroxyl (OH) radical reactivity (k(OH)) has been measured for 18 years with different measurement techniques. In order to compare the performances of instruments deployed in the field, two campaigns were conducted performing experiments in the atmospheric simulation chamber SAPHIR at Forschungszentrum Julich in October 2015 and April 2016. Chemical conditions were chosen either to be representative of the atmosphere or to test potential limitations of instruments. All types of instruments that are currently used for atmospheric measurements were used in one of the two campaigns. The results of these campaigns demonstrate that OH reactivity can be accurately measured for a wide range of atmospherically relevant chemical conditions (e.g. water vapour, nitrogen oxides, various organic compounds) by all instruments. The precision of the measurements (limit of detection < 1 s(-1) at a time resolution of 30 s to a few minutes) is higher for instruments directly detecting hydroxyl radicals, whereas the indirect comparative reactivity method (CRM) has a higher limit of detection of 2 s(-1) at a time resolution of 10 to 15 min. The performances of the instruments were systematically tested by stepwise increasing, for example, the concentrations of carbon monoxide (CO), water vapour or nitric oxide (NO). In further experiments, mixtures of organic reactants were injected into the chamber to simulate urban and forested environments. Overall, the results show that the instruments are capable of measuring OH reactivity in the presence of CO, alkanes, alkenes and aromatic compounds. The transmission efficiency in Teflon inlet lines could have introduced systematic errors in measurements for low-volatile organic compounds in some instruments. CRM instruments exhibited a larger scatter in the data compared to the other instruments. The largest differences to reference measurements or to calculated reactivity were observed by CRM instruments in the presence of terpenes and oxygenated organic compounds (mixing ratio of OH reactants were up to 10 ppbv). In some of these experiments, only a small fraction of the reactivity is detected. The accuracy of CRM measurements is most likely limited by the corrections that need to be applied to account for known effects of, for example, deviations from pseudo first-order conditions, nitrogen oxides or water vapour on the measurement. Methods used to derive these corrections vary among the different CRM instruments. Measurements taken with a flow-tube instrument combined with the direct detection of OH by chemical ionisation mass spectrometry (CIMS) show limitations in cases of high reactivity and high NO concentrations but were accurate for low reactivity (< 15 s(-1)) and low NO (< 5 ppbv) conditions.