Material Measurement Laboratory, National Institute of Standards and Technology , Gaithersburg, Maryland 20899, United States.
Environ Sci Technol. 2014 Mar 18;48(6):3169-76. doi: 10.1021/es4041804. Epub 2014 Feb 27.
We report the first mass-specific absorption and extinction cross sections for size- and mass-selected laboratory-generated soot aerosol. Measurement biases associated with aerosols possessing multiple charges were eliminated using mass selection to isolate singly charged particles for a specified electrical mobility diameter. Aerosol absorption and extinction coefficients were measured using photoacoustic and cavity ring-down spectroscopy techniques, respectively, for lacey and compacted soot morphologies. The measurements show that the mass-specific absorption cross sections are proportional to particle mass and independent of morphology, with values between 5.7 and 6 m(2) g(-1). Mass-specific extinction cross sections were morphology dependent and ranged between 12 and 16 m(2) g(-1) for the lacey and compact morphologies, respectively. The resulting single-scattering albedos ranged from 0.5 to 0.6. Results are also compared to theoretical calculations of light absorption and scattering from simulated particle agglomerates. The observed absorption is relatively well modeled, with minimum differences between the calculated and measured mass absorption cross sections ranging from ∼ 5% (lacey soot) to 14% (compact soot). The model, however, was unable to satisfactorily reproduce the measured extinction, underestimating the single-scattering albedo for both particle morphologies. These discrepancies between calculations and measurements underscore the need for validation and refinement of existing models of light scattering and absorption by soot agglomerates.
我们报告了首次针对大小和质量选择的实验室生成的烟灰气溶胶的比质量吸收和消光截面。通过质量选择消除了具有多个电荷的气溶胶的测量偏差，从而可以为特定的电迁移率直径隔离单电荷颗粒。使用光声和腔环衰减光谱技术分别测量了气溶胶的吸收和消光系数，用于测量疏松和密实的烟灰形态。测量结果表明，比质量吸收截面与颗粒质量成正比，与形态无关，值在 5.7 到 6 m²/g 之间。比质量消光截面取决于形态，疏松形态和密实形态的比质量消光截面分别在 12 到 16 m²/g 之间。由此产生的单次散射反照率在 0.5 到 0.6 之间。结果还与模拟粒子团聚体的光吸收和散射的理论计算进行了比较。观察到的吸收得到了很好的模拟，计算和测量的质量吸收截面之间的最小差异范围在 5%（疏松烟灰）到 14%（密实烟灰）之间。但是，该模型无法令人满意地再现测量的消光，低估了两种颗粒形态的单次散射反照率。这些计算与测量之间的差异突显了对现有的烟灰团聚体光散射和吸收模型进行验证和改进的必要性。
