Abstract Simultaneous transmissivity and absorptivity measurements were carried out in the visible at a laser wavelength of 532 nm on drop-cast, carbon-black-laden filters under ambient (laboratory) conditions. The focus of this investigation was to establish the feasibility of this approach to estimate the mass absorption coefficient of the isolated particles and compare results to earlier work with the same carbon-black source. Transmissivity measurements were carried out with a laser probe beam positioned normal to the particle-laden filter surface. Absorptivity measurements were carried out using a laser-heating approach to record in time the sample temperature rise to steady-state and decay back to the ambient temperature. The sample temperature was recorded using a fine-wire thermocouple that was integrated into the transmission arrangement by placing the thermocouple flush with the filter back surface. The advantage of this approach is that the sample absorptivity can be determined directly (using laser heating) instead of resolving the difference between reflectivity (filter surface scattering) and transmissivity. The current approach also provides the filter optical characteristics, as well as an estimate of filter effects on the absorption coefficient due to particle absorption enhancement or shadowing. The approach may also be incorporated into other filter-based techniques, like the particle/soot absorption photometer, with the simple addition of a thermocouple to the commercial instrument. For this investigation, measurements were carried out with several blank uncoated quartz filters. A range of solution concentrations was prepared with a well-characterized carbon black in deionized water (i.e., a water-soluble carbonaceous material referred to as a surrogate black carbon or ‘carbon black’). The solution was then drop cast using a calibrated syringe onto blank filters to vary particle loading. After evaporation of the water, the measurements were repeated with the coated filters. The measurement repeatability (95% confidence level) was better than 0.3 K for temperature and 3 × 10−5 mW for laser power. From the measurements with both the blank and coated filters, the absorption coefficient was determined for the isolated particles. The results were then compared with an earlier investigation by You et al. and Zangmeister and Radney, who used the same carbon-black material. The measurements were also compared with Lorenz–Mie computations for a polydispersion of spherical particles dispersed throughout a volume representative of the actual particles. The mass absorption coefficient for the polydispersion of carbon-black particles was estimated to be about 7.7 ± 1.4 m2 g−1, which was consistent with the results expected for these carbon black particles.

中文翻译：

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滴铸颗粒过滤器吸收炭黑的同时透射和吸收光度法

摘要 在环境（实验室）条件下，在 532 nm 激光波长下，在滴铸、载有炭黑的滤光片上同时进行透射率和吸收率测量。这项调查的重点是确定这种方法的可行性，以估计孤立颗粒的质量吸收系数，并将结果与​​早期使用相同炭黑源的工作进行比较。透射率测量是用垂直于载有颗粒的过滤器表面定位的激光探测光束进行的。使用激光加热方法进行吸收率测量，以及时记录样品温度上升到稳态并衰减回环境温度的时间。使用细线热电偶记录样品温度，该热电偶通过将热电偶与过滤器背面齐平而集成到传输装置中。这种方法的优点是可以直接确定样品吸收率（使用激光加热），而不是解决反射率（过滤器表面散射）和透射率之间的差异。当前方法还提供滤波器光学特性，以及由于粒子吸收增强或阴影对吸收系数的滤波器影响的估计。该方法还可以结合到其他基于过滤器的技术中，例如粒子/烟尘吸收光度计，只需将热电偶添加到商业仪器即可。对于这次调查，测量是用几个空白的无涂层石英滤光片进行的。用在去离子水中充分表征的炭黑（即，称为替代炭黑或“炭黑”的水溶性含碳材料）制备一系列溶液浓度。然后使用校准注射器将溶液滴注到空白过滤器上以改变颗粒负载。水蒸发后，用带涂层的过滤器重复测量。测量重复性（95% 置信水平）优于 0.3 K 的温度和 3 × 10−5 mW 的激光功率。根据对空白过滤器和带涂层过滤器的测量结果，确定了分离颗粒的吸收系数。然后将结果与 You 等人的早期调查进行了比较。还有Zangmeister和Radney，谁用了同样的炭黑材料。测量值也与 Lorenz-Mie 计算进行了比较，以得到分散在代表实际颗粒的体积中的球形颗粒的多分散。炭黑颗粒多分散体的质量吸收系数估计约为 7.7 ± 1.4 m2 g-1，这与这些炭黑颗粒的预期结果一致。