Optical properties of meteoric smoke analogues

Accurate determination of the optical properties of analogues for meteoric smoke particles 12 (MSPs), which are thought to be composed of iron-rich oxides or silicates, is important for their 13 observation and characterization in the atmosphere. In this study, a photochemical aerosol flow 14 reactor (PAFS) has been used to measure the optical extinction of iron oxide MSP analogues in 15 the wavelength range 325-675 nm. The particles were made photochemically, and agglomerate 16 into fractal-like particles with sizes on the order of 100 nm. Analysis using Transmission 17 Electron Microscopy (TEM), Energy Dispersive X-ray spectroscopy (EDX) and Electron Energy 18 Loss Spectroscopy (EELS) suggested the particles were most likely maghemite-like (γ-Fe2O3) in 19 composition. The optical extinction coefficients measured using the PAFS were then combined 20 with maghemite absorption coefficients measured using a complementary experimental system, 21 the MICE-TRAPS, to derive complex refractive indices which are able to reproduce both the 22 measured absorption and extinction.