You Rian, Radney James G, Zachariah Michael R, Zangmeister Christopher D
Material Measurement Laboratory, National Institute of Standards and Technology , Gaithersburg, Maryland 20899, United States.
Department of Chemistry and Biochemistry, University of Maryland , College Park, Maryland 20742, United States.
Environ Sci Technol. 2016 Aug 2;50(15):7982-90. doi: 10.1021/acs.est.6b01473. Epub 2016 Jul 14.
Optical absorption spectra of laboratory generated aerosols consisting of black carbon (BC) internally mixed with nonabsorbing materials (ammonium sulfate, AS, and sodium chloride, NaCl) and BC with a weakly absorbing brown carbon surrogate derived from humic acid (HA) were measured across the visible to near-IR (550 to 840 nm). Spectra were measured in situ using a photoacoustic spectrometer and step-scanning a supercontinuum laser source with a tunable wavelength and bandwidth filter. BC had a mass-specific absorption cross section (MAC) of 7.89 ± 0.25 m(2) g(-1) at λ = 550 nm and an absorption Ångström exponent (AAE) of 1.03 ± 0.09 (2σ). For internally mixed BC, the ratio of BC mass to the total mass of the mixture was chosen as 0.13 to mimic particles observed in the terrestrial atmosphere. The manner in which BC mixed with each material was determined from transmission electron microscopy (TEM). AS/BC and HA/BC particles were fully internally mixed, and the BC was both internally and externally mixed for NaCl/BC particles. The AS/BC, NaCl/BC, and HA/BC particles had AAEs of 1.43 ± 0.05, 1.34 ± 0.06, and 1.91 ± 0.05, respectively. The observed absorption enhancement of mixed BC relative to the pure BC was wavelength dependent for AS/BC and decreased from 1.5 at λ = 550 nm with increasing wavelength while the NaCl/BC enhancement was essentially wavelength independent. For HA/BC, the enhancement ranged from 2 to 3 and was strongly wavelength dependent. Removal of the HA absorption contribution to enhancement revealed that the enhancement was ≈1.5 and independent of wavelength.
测量了实验室生成的气溶胶的光吸收光谱，这些气溶胶由内部混合了非吸收性物质（硫酸铵，AS，和氯化钠，NaCl）的黑碳（BC）以及含有源自腐殖酸（HA）的弱吸收性棕碳替代物的BC组成，测量范围为可见光到近红外（550至840nm）。使用光声光谱仪原位测量光谱，并通过可调谐波长和带宽滤波器对超连续激光源进行步进扫描。BC在λ = 550nm处的质量比吸收截面（MAC）为7.89±0.25 m² g⁻¹，吸收埃指数（AAE）为1.03±0.09（2σ）。对于内部混合的BC，BC质量与混合物总质量的比例选择为0.13，以模拟在地球大气中观测到的颗粒。BC与每种材料的混合方式通过透射电子显微镜（TEM）确定。AS/BC和HA/BC颗粒完全内部混合，而NaCl/BC颗粒的BC既有内部混合也有外部混合。AS/BC、NaCl/BC和HA/BC颗粒的AAE分别为1.43±0.05、1.34±0.06和1.91±0.05。相对于纯BC，混合BC观察到的吸收增强对于AS/BC是波长依赖性的，并且从λ = 550nm处的1.5随着波长增加而降低，而NaCl/BC的增强基本上与波长无关。对于HA/BC，增强范围为2至3，并且强烈依赖于波长。去除HA对增强的吸收贡献表明增强约为1.5且与波长无关。
