Optical properties of meteoric smoke analogues

Abstract

Abstract. Accurate determination of the optical properties of analogues for meteoric smoke particles (MSPs), which are thought to be composed of iron-rich oxides or silicates, is important for their observation and characterization in the atmosphere. In this study, a photochemical aerosol flow system (PAFS) has been used to measure the optical extinction of iron oxide MSP analogues in the wavelength range 325–675 nm. The particles were made photochemically and agglomerate into fractal-like particles with sizes on the order of 100 nm. Analysis using transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS) suggested the particles were most likely maghemite-like (γ-Fe2O3) in composition, though a magnetite-like composition could not be completely ruled out. Assuming a maghemite-like composition, the optical extinction coefficients measured using the PAFS were combined with maghemite absorption coefficients measured using a complementary experimental system (the MICE-TRAPS) to derive complex refractive indices that reproduce both the measured absorption and extinction.

Opinion: Recent developments and future directions in studying the mesosphere and lower thermosphere

“…Recent laboratory work has played an important role in understanding the microphysics and chemistry of MSPs with respect to the determination of the optical properties of MSP analogues, which is important for atmospheric observations (Aylett et al, 2019); a confirmation that meteoric smoke particles can provide nuclei for heterogeneous ice formation in NLCs (Duft et al, 2019); the effect of solar radiation on ice particle formation (Nachbar et al, 2019); a demonstration that MSPs provide an active surface for heterogeneous chemistry, e.g. altering the nighttime HO 2 /OH ratio (James et al, 2017); and that MSP analogues and meteoritic fragments are effective heterogeneous nuclei for crystal formation of nitric acid trihydrate (NAT) in the absence of water ice in polar stratospheric clouds (James et al, 2023).…”

Opinion: Recent Developments and Future Directions in Studying the Chemistry of the Mesosphere and Lower Thermosphere

“…Recent laboratory work has played an important role in understanding the microphysics and chemistry of MSPs: determination of the optical properties of MSP analogues, which is important for atmospheric observations (Aylett et al, 2019); confirmation that meteoric smoke particles can provide nuclei for heterogeneous ice formation in NLCs (Duft et al, 2019); the impact of solar radiation on ice particle formation (Nachbar et al, 2019); demonstration that MSPs provide an active surface for heterogeneous chemistry e.g. altering the nighttime HO2/OH ratio (James et al, 2017); and that MSP analogues and meteoritic fragments are effective heterogeneous nuclei for crystal formation of nitric acid trihydrate (NAT)…”