Hamilton Richard P, Heal Mathew R
School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JJ, UK.
J Environ Monit. 2004 Jan;6(1):12-7. doi: 10.1039/b311869j. Epub 2003 Nov 17.
This study was carried out in response to suggestions that the measurement of NO(2) by Palmes-type passive diffusion tubes (PDT) is affected by the method of preparation of the triethanolamine (TEA) absorbent coating on the grids. The following combinations of factors were investigated: TEA solvent (acetone or water), volume composition of TEA in solvent (50% or 20%), and grid coating method (dipping in solution prior to assembly or pipetting solution on after assembly). Duplicate PDTs prepared by each of the 8 methods were exposed in parallel, in urban air, for a total of 80 separate 1 week exposures. NO(2) concentrations derived from PDTs prepared by pipetting methods were significantly less precise than concentrations from dipping methods, with mean RSDs for duplicate measurements of 13.8% and 8.5%, respectively (n= 316 each category). Pipetting methods using solutions of 50% TEA composition were particularly imprecise (mean RSD 17.2%). Data from PDTs prepared by pipetting methods were systematically more poorly correlated with each other and with data from co-located chemiluminescence analysers, than corresponding data from PDTs prepared by dipping methods, indicating that more consistent accuracy was also obtained by the latter PDTs. The statistical evidence suggested that PDTs prepared by pipetting 50% TEA in water generally gave lower NO(2) concentrations. Although this is in agreement with a previous study, it is also possible that such an observation here may be a statistical artefact given the demonstrably poorer precision of this method. The general tendency of PDTs to show positive bias in NO(2) measurement in urban air in 1 week exposures was again evident in this study (mean biases at roadside and urban centre locations of +35% (n= 475) and +18% (n= 112), respectively) consistent with augmentation of within-tube NO(2) flux by chemical reaction between co-diffusing NO and O(3). Overall, it is recommended that the pipetting method of PDT grid preparation is avoided, or at least investigated further, because of the apparent degradation in precision and accuracy of NO(2) measurement. Potential reasons for the effect are discussed.
本研究是针对有关帕尔姆斯型被动扩散管（PDT）对二氧化氮（NO₂）的测量受网格上三乙醇胺（TEA）吸收涂层制备方法影响的建议而开展的。研究了以下因素组合：TEA溶剂（丙酮或水）、溶剂中TEA的体积组成（50%或20%）以及网格涂层方法（组装前浸入溶液或组装后用移液管滴加溶液）。通过这8种方法制备的成对PDT在城市空气中并行暴露，总共进行80次单独的为期1周的暴露。通过移液法制备的PDT得出的NO₂浓度精度明显低于浸渍法得出的浓度，重复测量的平均相对标准偏差分别为13.8%和8.5%（每类n = 316）。使用50%TEA组成溶液的移液法尤其不精确（平均相对标准偏差为17.2%）。与浸渍法制备的PDT的相应数据相比，移液法制备的PDT的数据彼此之间以及与并置的化学发光分析仪的数据之间的系统相关性更差，这表明后一种PDT也获得了更一致的准确性。统计证据表明，通过在水中移液50%TEA制备的PDT通常给出较低的NO₂浓度。尽管这与先前的一项研究一致，但鉴于该方法明显较差的精度，此处的这种观察结果也可能是一种统计假象。在本研究中，PDT在城市空气中1周暴露的NO₂测量中显示出正偏差的总体趋势再次明显（路边和城市中心位置的平均偏差分别为+35%（n = 475）和+18%（n = 112）），这与共扩散的NO和O₃之间的化学反应增强管内NO₂通量一致。总体而言，建议避免使用移液法制备PDT网格，或者至少进一步研究，因为NO₂测量的精度和准确性明显下降。讨论了产生这种影响的潜在原因。
