Mass extinction spectra and size distribution measurements of quartz and amorphous silica aerosol at 0.33-19 mu m compared to modelled extinction using Mie, CDE, and T-matrix theories

作者：Reed Benjamin E^*; Peters Daniel M; McPheat Robert; Smith Andrew J A; Grainger R G

来源：Journal of Quantitative Spectroscopy and Radiative Transfer, 2017, 199: 52-65.

DOI：10.1016/j.jqsrt.2017.05.011

• Mass extinction coefficient
• Aerosols
• Quartz
• Amorphous silica
• Mie theory
• Non-spherical scattering
• T-matrix theory
• Rayleigh CDE model

Simultaneous measurements were made of the spectral extinction (from 0.33-19 pm) and particle size distribution of silica aerosol dispersed in nitrogen gas. Two optical systems were used to measure the extinction spectra over a wide spectral range: a Fourier transform spectrometer in the infrared and two diffraction grating spectrometers covering visible and ultraviolet wavelengths. The particle size distribution was measured using a scanning mobility particle sizer and an optical particle counter. The measurements were applied to one amorphous and two crsystalline silica (quartz) samples. In the infrared peak values of the mass extinction coefficient (MEC) of the crystalline samples were 1.63 +/- 0.23 m(2)g(-1) at 9.06 mu m and 1.53 +/- 0.26 m(2)g(-1) at 9.14 gm with corresponding effective radii of 0.267 and 0.331 mu m, respectively. For the amorphous sample the peak MEC value was 1.37 +/- 0.18 m(2)g(-1) at 8.98 prn and the effective radius of the particles was 0.374).un. Using the measured size distribution and literature values of the complex refractive index as inputs, three scattering models were evaluated for modelling the extinction: Mie theory, the Rayleigh continuous distribution of ellipsoids (CDE) model, and T -matrix modelling of a distribution of spheroids. Mie theory provided poor fits to the infrared extinction of quartz (R-2 < 0.19), although the discrepancies were significantly lower for Mie theory and the amorphous silica sample (R-2 = 0.86). The CDE model provided improved fits in the infrared compared to Mie theory, with R-2 > 0.82 for crsytalline sillica and R-2 = 0.98 for amorphous silica. The T -matrix approach was able to fit the amorphous infrared extinction data with an R-2 value of 0.995. Allowing for the possibility of reduced crystallinity in the milled crystal samples, using a mixture of amorphous and crystalline T -matrix cross-sections provided fits with R-2 values greater than 0.97 for the infrared extinction of the crystalline samples.

• 出版日期2017-9