Presser Cary, Nazarian Ashot, Conny Joseph M, Chand Duli, Sedlacek Arthur, Hubbe John M
National Institute of Standards and Technology.
Pacific Northwest National Laboratory.
Aerosol Sci Technol. 2017;51(4):451-466. doi: 10.1080/02786826.2016.1267856. Epub 2016 Dec 2.
Absorptivity measurements with a laser-heating approach, referred to as the laser-driven thermal reactor (LDTR), were carried out in the infrared and applied at ambient (laboratory) non-reacting conditions to particle-laden filters from a three-wavelength (visible) particle/soot absorption photometer (PSAP). The particles were obtained during the Biomass Burning Observation Project (BBOP) field campaign. The focus of this study was to determine the particle absorption coefficient from field-campaign filter samples using the LDTR approach, and compare results with other commercially available instrumentation (in this case with the PSAP, which has been compared with numerous other optical techniques). Advantages of the LDTR approach include 1) direct estimation of material absorption from temperature measurements (as opposed to resolving the difference between the measured reflection/scattering and transmission), 2) information on the filter optical properties, and 3) identification of the filter material effects on particle absorption (e.g., leading to particle absorption enhancement or shadowing). For measurements carried out under ambient conditions, the particle absorptivity is obtained with a thermocouple placed flush with the filter back surface and the laser probe beam impinging normal to the filter particle-laden surface. Thus, in principle one can employ a simple experimental arrangement to measure simultaneously both the transmissivity and absorptivity (at different discrete wavelengths) and ascertain the particle absorption coefficient. For this investigation, LDTR measurements were carried out with PSAP filters (pairs with both blank and exposed filters) from eight different days during the campaign, having relatively light but different particle loadings. The observed particles coating the filters were found to be carbonaceous (having broadband absorption characteristics). The LDTR absorption coefficient compared well with results from the PSAP. The analysis was also expanded to account for the filter fiber scattering on particle absorption in assessing particle absorption enhancement and shadowing effects. The results indicated that absorption enhancement effects were significant, and diminished with increased filter particle loading.
采用激光加热方法（称为激光驱动热反应器，LDTR）进行吸收率测量，测量在红外波段进行，并应用于在环境（实验室）非反应条件下，来自三波长（可见光）颗粒/烟尘吸收光度计（PSAP）的含颗粒过滤器。颗粒是在生物质燃烧观测项目（BBOP）野外考察期间获得的。本研究的重点是使用LDTR方法从野外考察过滤器样本中确定颗粒吸收系数，并将结果与其他商用仪器（在本案例中为PSAP，其已与许多其他光学技术进行了比较）的结果进行比较。LDTR方法的优点包括：1）通过温度测量直接估计材料吸收率（与解析测量的反射/散射和透射之间的差异相反）；2）关于过滤器光学特性的信息；3）识别过滤器材料对颗粒吸收的影响（例如，导致颗粒吸收增强或遮蔽）。对于在环境条件下进行的测量，颗粒吸收率是通过将热电偶与过滤器背面齐平放置，并使激光探测光束垂直入射到过滤器含颗粒表面来获得的。因此，原则上可以采用简单的实验装置同时测量透射率和吸收率（在不同的离散波长），并确定颗粒吸收系数。对于本研究，在考察期间的八个不同日期，使用PSAP过滤器（空白和暴露过滤器对）进行了LDTR测量，这些过滤器具有相对较轻但不同的颗粒负载。发现覆盖在过滤器上的观测颗粒是含碳的（具有宽带吸收特性）。LDTR吸收系数与PSAP的结果比较良好。分析还扩展到在评估颗粒吸收增强和遮蔽效应时考虑过滤器纤维对颗粒吸收的散射。结果表明，吸收增强效应显著，并且随着过滤器颗粒负载的增加而减弱。
