The uptake of HO₂ on meteoric smoke analogues

Abstract

The kinetics of heterogeneous HO2 uptake onto meteoric smoke particles (MSPs) has been studied in the laboratory using analogues of MSP aerosol entrained into a flow tube. The uptake coefficient, γ, was determined on synthetic amorphous olivine (MgFeSiO4) to be (6.9 ± 1.2) × 10−2 at a relative humidity (RH) of 10%. On forsterite (Mg2SiO4), γ = (4.3 ± 0.4) × 10−3 at RH = 11.6% and (7.3 ± 0.4) × 10−2 at RH = 9.9% on fayalite (Fe2SiO4). These results indicate that Fe plays a more important mechanistic role than Mg in the removal of HO2 from the gas phase. Electronic structure calculations show that Fe atoms exposed at the particle surface provide a catalytic site where HO2 is converted to H2O2 via an Eley‐Rideal mechanism, but this does not occur on exposed surface Mg atoms. The impact of this heterogeneous process in the middle atmosphere was then investigated using a whole atmosphere chemistry‐climate model which incorporates a microphysical treatment of MSPs. Using a global MSP production rate from meteoric ablation of 44 t/day, heterogeneous uptake (with γ = 0.2) on MSPs significantly alters the HOx budget in the nighttime polar vortex. This impact is highly latitude dependent and thus could not be confirmed using currently available satellite measurements of HO2, which are largely unavailable at latitudes greater than 70°.

Heterogeneous reactions of mineral dust aerosol: implications for tropospheric oxidation capacity

“…It appears that compared to meteoric smoke particles which do not contain Fe, Fe-containing meteoric smoke particles show much larger heterogeneous reactivity towards HO 2 radicals. The experimental result indicates a catalytic role of Fe in HO 2 uptake, as supported by electronic structure calculations (James et al, 2017). Though its tropospheric relevance is limited, this study provides valuable mechanistic insights into the heterogeneous reaction of mineral dust with HO 2 radicals.…”

“…Apart from these displayed in Fig. 6, the uptake of HO 2 by analogues of meteoric smoke particles was also examined at room temperature (James et al, 2017), using an aerosol flow tube. At (10 ± 1) % RH, the uptake coefficient was determined to be 0.069 ± 0.012 for olivine (MgFeSiO 4 ), 0.073 ± 0.004 for fayalite (Fe 2 SiO 4 ), and 0.0043 ± 0.0004 for forsterite (Mg 2 SiO 4 ).…”

Constraints on Meteoric Smoke Composition and Meteoric Influx Using SOFIE Observations With Models

“…The present study uses observations from the Solar Occultation For Ice Experiment (SOFIE) at three wavelengths to constrain the composition of smoke particles in the mesosphere. Smoke composition is important for ion and neutral chemistry in the mesosphere and upper stratosphere (Frankland et al, ; James et al, ; Summers & Siskind, ), is relevant to the nucleation of polar mesospheric clouds (PMCs) (Havnes & Næsheim, ) and stratospheric aerosols, and is germane to astronomy. In addition, the interpretation of smoke observations will benefit from knowledge of smoke composition.…”

Impacts of Cosmic Dust on Planetary Atmospheres and Surfaces

“…There has been a great deal of work in the past decade on meteoric smoke particles. This has included laboratory investigations into MSP formation (Saunders and Plane 2006) and ice-nucleating ability (Nachbar et al 2016); detection in the terrestrial atmosphere by rocket payloads , radar ) and optical extinction (Hervig et al 2009); and modelling impacts through providing a surface for heterogeneous chemistry (Frankland et al 2016;James et al 2017b) and ice nuclei for the formation of mesospheric clouds on Earth (Rapp and Thomas 2006;Hervig et al 2012) and Mars (Määttänen et al 2013;Listowski et al 2014). The role of MSPs in the formation of sulphuric acid particles in Venus, and polar stratospheric clouds in the terrestrial atmosphere, still needs to be better understood.…”

“…Frankland et al (2015) used a laboratory measurement of the uptake coefficient of HNO 3 on MSP analogue particles to show that heterogeneous removal on MSPs in the winter polar vortex between 30 and 60 km should provide an important sink for HNO 3 . Similarly, heterogeneous uptake of the HO 2 radical on MSPs, which is sensitive to the fraction of Fe in the particles, should significantly alter the general radical chemistry of the nighttime polar vortex (James et al 2017b). …”