Light absorption and morphological properties of soot-containing aerosols observed at an East Asian outflow site, Noto Peninsula, Japan
Light absorption and morphological properties of soot-containing aerosols observed at an East Asian outflow site, Noto Peninsula, Japan
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DOI：
10.5194/acp-16-2525-2016
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发表时间：
2015-09
影响因子：
6.3
通讯作者：
Sayako Ueda;T. Nakayama;F. Taketani;K. Adachi;A. Matsuki;Yoko Iwamoto;Y. Sadanaga;Y. Matsumi
中科院分区：
文献类型：
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作者：
Sayako Ueda;T. Nakayama;F. Taketani;K. Adachi;A. Matsuki;Yoko Iwamoto;Y. Sadanaga;Y. Matsumi
抽象。用无机盐和有机化合物涂覆黑碳（BC）可以增强BC的光吸收幅度。为了阐明老化BC颗粒的光吸收增强及其与单个颗粒的混合状态和形态的关系，我们于2013年春季在日本诺托半岛的亚洲外流站点进行了颗粒观测。在通过维持在300或400 °C的热扩散器（TD）或维持在室温（25 °C）的旁路管线之后，分别使用三波长光声烟尘光谱仪和单颗粒烟尘光度计（SP2）测量PM2.5中的难降解BC在405、532和781 nm处的吸收和散射系数以及质量浓度/混合状态。通过比较在300 °C下穿过和不穿过TD的颗粒在781 nm处的吸收系数来估计由于涂层引起的BC光吸收的平均增强因子，发现其为1.22。最大的增强（> 1.30）在高吸收系数时期，当空气质量的长距离输送从中国的城市地区。气溶胶样品也进行了分析，使用透射电子显微镜（TEM）配备了能量色散X射线分析仪。通过对比高密度电子束辐照蒸发束敏感材料前后的显微照片，分析了在高吸收事件中收集的四个样品中含烟颗粒的形态特征和混合状态。在所有样品中的烟尘的大部分被发现作为混合颗粒与含硫酸盐的小球或作为集群的这种小球。对于显示BC光吸收的高增强（> 1.30）的样品，TEM显示内部混合的含烟灰颗粒倾向于具有更球形的形状并且被厚涂覆。SP2测量还表明，厚涂层烟灰的比例更大。因此，所观察到的BC光吸收的增强被认为是不同的，根据混合状态和含烟颗粒的形态。在我们的原位测量中BC光吸收的增强及其与含烟颗粒的个体特征的关系将有助于评估BC的大排放源的顺风区域的直接辐射强迫。
Abstract. The coating of black carbon (BC) with inorganic salts and organic compounds can enhance the magnitude of light absorption by BC. To elucidate the enhancement of light absorption of aged BC particles and its relation to the mixing state and morphology of individual particles, we conducted observations of particles at an Asian outflow site in Noto Peninsula, Japan, in the spring of 2013. Absorption and scattering coefficients at 405, 532, and 781 nm and mass concentrations/mixing states of refractory BC in PM2.5 were measured using a three-wavelength photoacoustic soot spectrometer and a single-particle soot photometer (SP2), respectively, after passage through a thermodenuder (TD) maintained at 300 or 400 °C or a bypass line maintained at room temperature (25 °C). The average enhancement factor of BC light absorption due to coating was estimated by comparing absorption coefficients at 781 nm for particles that with and without passing through the TD at 300 °C and was found to be 1.22. The largest enhancements (> 1.30) were observed under high absorption coefficient periods when the air mass was long-range transported from urban areas in China. Aerosol samples were also analyzed using a transmission electron microscope (TEM) equipped with an energy dispersive X-ray analyzer. The morphological features and mixing states of soot-containing particles of four samples collected during the high absorption events were analyzed by comparing microphotographs before and after the evaporation of beam-sensitive materials by irradiation with a high-density electron beam. The majority of the soot in all samples was found as mixed particles with sulfate-containing spherules or as clusters of such spherules. For samples showing high enhancement (> 1.30) of BC light absorption, the TEM showed that the internally mixed soot-containing particles tended to have a more spherical shape and to be thickly coated. The SP2 measurements also suggested that the proportion of thickly coated soot was greater. Thus, the observed enhancement of BC light absorption was found to differ according to the mixing states and morphology of soot-containing particles. The enhancement of BC light absorption in our in situ measurements and its relation with individual features of soot-containing particles will be useful to evaluate direct radiative forcing in the downwind areas of large emission sources of BC.