Calibration of a Condensation Particle Counter Using a NIST Traceable Method
Calibration of a Condensation Particle Counter Using a NIST Traceable Method
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DOI：
10.1080/02786820802716735
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发表时间：
2009-01-01
影响因子：
5.2
通讯作者：
Klinedinst, D. B.
中科院分区：
文献类型：
--
作者：
Fletcher, R. A.;Mulholland, G. W.;Klinedinst, D. B.
本文介绍了一种使用美国国家标准与技术研究所(NIST)可追溯方法对商用凝结粒子计数器进行校准的方法。根据计量学的性质，这项工作还比较了三种测量气溶胶浓度的独立技术的测量结果：连续流动冷凝颗粒计数器(CPC)、气溶胶静电计(AE)和从微观颗粒计数得出的气溶胶浓度。由于气溶胶的瞬变性质，没有像颗粒直径标准那样存在的浓度伪影标准。我们使用一种流动性分类器来生产一种几乎单分散、80 nm的聚苯乙烯乳胶气雾剂。测试气溶胶被用作对CPC和AE的挑战，随后对其进行过滤采样以进行电子显微镜检查。我们的试验台设计包含一个连续的CPC气溶胶浓度监测仪，以验证气溶胶的稳定性。CPC通过在恒定样品流速下进行单颗粒计数来确定颗粒浓度。AE已根据NIST可追溯的电流标准进行了校准。随后的气溶胶浓度测量是通过确定由控制的气溶胶流速输送到探测器的带电气溶胶所产生的电流来获得的。我们对所有方法的流量都有NIST可追溯性，并有一套方法来校准AE到NIST可追溯的电气标准。后者提供了气溶胶衍生电流测量中的校准和不确定度的确定。通过使用电喷雾气溶胶发生器产生挑战粒子，观察到并克服了由于多个带电粒子造成的测量偏差。该发生器能够产生100个粒子/厘米(3)到15000个粒子/厘米(3)的气溶胶浓度，二聚体粒子的数量较少(约为1%)。在我们的工作中，气溶胶浓度的独立测量是通过在小孔过滤材料上定量采集气载聚苯乙烯乳胶球的样品并通过电子显微镜测定采集到的颗粒物的数量来实现的。使用场发射扫描电子显微镜获得的电子显微图像用颗粒计数法进行了分析。我们发现，当颗粒浓度约为120个/厘米(3)时，气溶胶静电计测量的相对不确定度超过100%，而当浓度大于6000个/厘米(3)时，相对不确定度约为5%。显微镜方法的不确定度约为3%。
This work presents a calibration of a commercial condensation particle counter using National Institute of Standards and Technology (NIST) traceable methods. By the nature of the metrology involved, this work also compares the measurement results of three independent techniques for measuring aerosol concentration: continuous flow condensation particle counter (CPC); aerosol electrometer (AE); and the aerosol concentration derived from microscopic particle counting. Because of the transient nature of aerosol, there are no concentration artifact standards such as exist for particle diameter standards. We employ a mobility classifier to produce a nearly monodisperse, 80 nm, polystyrene latex aerosol. The test aerosol is used as a challenge for the CPC and the AE, and is subsequently filter sampled for electron microscopy. Our test stand design incorporates a continuous CPC aerosol concentration monitor to verify the aerosol stability. The CPC determines particle concentration by single particle counting at a constant sample flow rate. The AE has been calibrated to a NIST traceable current standard. The subsequent aerosol concentration measurement is obtained by determining the electrical current produced by a charged aerosol transported to the detector by a controlled aerosol flow rate. We have NIST traceability for flow rates for all methods and a methodology to calibrate the AE to NIST traceable electrical standards. The latter provides a calibration and a determination of the uncertainty in the aerosol derived current measurement. A bias in the measurements due to multiple charged particles was observed and overcome by using an electrospray aerosol generator to produce the challenge particles. This generator was able to produce aerosol concentrations over the range of 100 particles/cm(3) to 15 000 particles/cm(3) with lower number of dimer particles (approximate to 1%). In our work, independent measurement of aerosol concentration is obtained by quantitatively collecting samples of the airborne polystyrene latex spheres on a small pore filter material and determining the number of particles collected by electron microscopy. Electron micrograph images obtained using a field-emission scanning electron microscope are analyzed using particle counting. We found the relative uncertainty in the aerosol electrometer measurements to be in excess of 100% for particle concentrations of approximately 120 particles/cm(3) and approximately 5% for concentrations above 6000 particles/cm(3). The uncertainty found by the microscopy method was approximately 3%.