Radney James G, Zangmeister Christopher D
National Institute of Standards and Technology, Material Measurement Laboratory, 100 Bureau Dr., Gaithersburg, Maryland, 20899, USA.
J Quant Spectrosc Radiat Transf. 2017 Jan;187:145-149. doi: 10.1016/j.jqsrt.2016.09.026. Epub 2016 Oct 6.
Photoacoustic spectroscopy measurements of flame-generated soot aerosol coated with small amounts of water yielded absorption enhancements that were dependent on the laser used: quasi-continuous wave (Q-CW, ≈ 650 ps pulse duration and 78 MHz repetition rate) versus continuous wave (CW). Water coating thickness was controlled by exposing the aerosol to a set relative humidity (RH). At ≈ 85 % RH, the mass of the soot particles increased by an amount comparable to a monolayer of water being deposited and enhanced the measured absorption by 36 % and 15 % for the Q-CW and CW lasers, respectively. Extinction measurements were also performed using a cavity ring-down spectrometer (extinction equals the sum of absorption and scattering) with a CW laser and negligible enhancement was observed at all RH. These findings demonstrate that source choice can impact measurements of aerosols with volatile coatings and that the absorption enhancements at high RH previously measured by Radney and Zangmeister (2015) [1] are the result of laser source used (Q-CW) and not from an increase in the particle absorption cross section.
准连续波（Q-CW，脉冲持续时间约650皮秒，重复频率78兆赫）与连续波（CW）。通过将气溶胶暴露于设定的相对湿度（RH）来控制水涂层的厚度。在约85%相对湿度下，碳烟颗粒的质量增加量与沉积单层水相当，对于Q-CW和CW激光，分别使测量的吸收增强了36%和15%。还使用腔衰荡光谱仪进行了消光测量（消光等于吸收和散射之和），使用CW激光，在所有相对湿度下观察到的增强可忽略不计。这些发现表明，光源选择会影响对具有挥发性涂层的气溶胶的测量，并且Radney和Zangmeister（2015年）[1]之前在高相对湿度下测量的吸收增强是所用激光源（Q-CW）的结果，而非颗粒吸收截面增加的结果。
