Laboratory Validation of Aerosol Extinction Coefficient Measurements by a Field-Deployable Pulsed Cavity Ring-Down Transmissometer
Laboratory Validation of Aerosol Extinction Coefficient Measurements by a Field-Deployable Pulsed Cavity Ring-Down Transmissometer
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通过现场可部署脉冲腔衰荡透射仪进行气溶胶消光系数测量的实验室验证
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发表时间：
2009
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通讯作者：
D. Atkinson
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作者：
J. Radney;M. Bazargan;Monica E. Wright;D. Atkinson
脉冲腔衰荡透射仪能够同时灵敏地测量两个波长(λ=532,1064 nm)的气溶胶消光系数。该仪器可与浊度计(测量同一气溶胶的530 nm散射系数)和颗粒计数器配合使用，以实现对气溶胶广泛而密集的光学性质和颗粒数浓度的现场测量。根据散射系数和消光系数的测量，可以计算气溶胶吸收系数，并可以确定单次散射反照率和消光指数。本文通过一系列的实验室实验对脉冲腔衰荡透射仪进行了验证。对于纯散射亚微米粒子，证明了腔衰荡透射仪的消光系数与浊度计的散射系数之间的一致性。然后，证明了当使用尺寸选定的测量数浓度的粒子时，测量消光与Mie理论之间的一致性。根据颗粒大小和组成的不同，与Mie理论的一致性从优秀(偏差小于1%)到边缘(12%)不等。已经观察到与Mie理论类似的偏差(Baynard等人)。2007)，我们认为这可能是由于多电荷粒子在尺寸选择(DMA)过程中的影响。对于CRD透射仪的消光测量，其检测和定量的95%置信限估计分别为BEXT=4.0 mm−1和13.4 mm−1(Skoog等人。2004年)。
A pulsed cavity ring-down transmissometer is shown here to be capable of sensitively measuring the aerosol extinction coefficient at two wavelengths (λ = 532, 1064 nm) simultaneously. This instrument can be coupled with a nephelometer (yielding a measurement of the 530 nm scattering coefficient of the same aerosol) and a particle counter to allow the in situ measurement of extensive and intensive optical properties and particle number concentrations of aerosols. From the scattering and extinction coefficient measurements, the aerosol absorption coefficient can be calculated and the intensive properties single scattering albedo and extinction Ångström exponent can be determined. In this report, the pulsed cavity-ring down transmissometer (CRDT) is validated through a series of laboratory experiments. Agreement between the extinction coefficients from the cavity ring-down transmissometer and the scattering coefficient from the nephelometer is demonstrated for purely scattering sub-micron particles. Then agreement between measured extinction and Mie theory is demonstrated when using size-selected particles of measured number concentration. The agreement with Mie theory ranges from excellent (less than 1% deviation) to marginal (12%) depending on the particle size and composition. Similar deviations from Mie theory have been observed (Baynard et al. 2007) and we suggest that they could be due to the influence of multiply charged particles in the size-selection (DMA) process. The 95% confidence level limits of detection and quantitation for the extinction measurement by the CRD transmissometer are estimated to be bext = 4.0 Mm−1 and 13.4 Mm−1, respectively (Skoog et al. 2004).