The ablation of phosphorus from interplanetary dust particles entering the Earth’s atmosphere is a potentially significant source of this key bio-element. In this study, the atmospheric chemistry of phosphorus is explored by developing a reaction network of possible routes from PO, the major ablation product in the upper mesosphere/lower thermosphere region, to the stable reservoirs H3PO3 and H3PO4 that become incorporated into meteoric smoke particles as metal phosphites and phosphates, respectively. The network is constructed with reactions whose kinetics have been measured experimentally, together with reactions where theoretical rate coefficients are estimated using a combination of electronic structure theory calculations and a Rice-Ramsperger-Kassel-Markus master equation treatment. The network is then incorporated into a global chemistry-climate model, together with a phosphorus meteoric input function. The estimated global mean P deposition flux, in the form of sub-micron sized meteoric smoke particles, is 1 × 10-8 g m-2 yr-1, with a maximum of ~5 × 10-8 g m-2 yr-1 over the northern Rockies, Himalayas and southern Andes. The estimated fraction of ablated phosphorus forming bio-available metal phosphites is 11%, which results from the very large concentrations of O and H compared to OH in the upper mesosphere. A layer of OPO is predicted to occur at 90 km with a peak of concentration of ~50 cm-3; this is the counterpart of the well-known layers of meteoric metals such as Na and Fe, and may be observable spectroscopically.

We use a 3-D chemical transport model and satellite observations to investigate Arctic ozone depletion in winter/spring 2019/20 and compare with earlier years. Persistently low temperatures caused extensive chlorine activation through to March. March-mean polar-cap-mean modelled chemical column ozone loss reached 78 DU (local maximum loss of ~108 DU in the vortex), similar to that in 2011. However, weak dynamical replenishment of only 59 DU from December to March was key to producing very low (<220 DU) column ozone values. The only other winter to exhibit such weak transport in the past 20 years was 2010/11, so this process is fundamental to causing such low ozone values. A model simulation with peak observed stratospheric total chlorine and bromine loading (from the mid-1990s) shows that gradual recovery of the ozone layer over the past two decades ameliorated the polar cap ozone depletion in March 2020 by ~20 DU.

Satellite observations of relevant trace gases, together with meteorological data from ERA5, were used to describe the dynamics and chemistry of the spectacular Arctic 2019/20 winter/spring season. Exceptionally low total ozone values of slightly less than 220 DU were observed in mid March within an unusually large stratospheric polar vortex. This was associated with very low temperatures and extensive polar stratospheric cloud formation, a prerequisite for substantial springtime ozone depletion. Very high OClO and very low NO2 column amounts observed by GOME-2A are indicative of unusually large active chlorine levels and significant denitrification, which likely contributed to large chemical ozone loss. Using results from the TOMCAT chemical transport model (CTM) and ozone observations from S5P/TROPOMI, GOME-2 (total column), SCIAMACHY and OMPS-LP (vertical profiles) chemical ozone loss was evaluated and compared with the previous record Arctic winter 2010/11. The polar-vortex-averaged total column ozone loss in 2019/20 reached 88 DU (23%) and 106~DU (28%) based upon observations and model, respectively, by the end of March, which was similar to that derived for 2010/11. The total column ozone loss is in agreement with OMPS-LP-derived partial column loss between 350 K and 550 K to within the uncertainty. The maximum ozone loss (~80%) observed by OMPS-LP was near the 450 K potential temperature level (~18 km altitude). Because of the larger polar vortex area in March 2020 compared to March 2011 (about 25% at 450 K), ozone mass loss was larger in Arctic winter 2019/20.

In this presentation I will explain an analysis of three different recovered remote-sensing measurements of the 1960s Northern Hemisphere mid-latitude stratospheric aerosol layer. Two of the datasets were recovered within student projects on the Leeds MRes in Climate and Atmospheric Science, the 3rd following a collaboration with Dr. Juan-Carlos Antuna Marrero (Univ. Valladolid, Spain) as part of a “data rescue activity” within the World Climate Research Program activity on stratospheric sulphur, SSiRC: http://www.sparc-ssirc.org/data/datarescueactivity.html Two of the datasets are for the 1963-1965 period when the tropical stratospheric reservoir was highly elevated following the two March 1963 Agung major eruptions (e.g. Niemeier et al., 2019): a series of searchlight measurements from White Sands, New Mexico during 1963 and 1964 (Elterman and Campbell, 1964; Elterman, 1966; Elterman et al., 1973), and the first ever multi-annual stratospheric aerosol dataset from the MIT lidar at Lexington, Massachussetts (Grams, 1966; Grams & Fiocco, 1967; Antuna Marrero et al., 2020). The 3rd dataset, from the 1966-67 period (after the Agung aerosol cloud had fully dispersed) is from two types of balloon measurements: a dust-sonde OPC (Rosen, 1964; Rosen, 1968) and solar-extinction-sounder (Rosen, 1969; Pepin, 1970) both balloon instruments measuring during a Sep 1966 field campaign in the tropics (Panama City, Panama) and a sustained set of NH mid-latitude measurements from Minneapolis, Minnesota in 1963-1967. The observations will be compared to interactive stratospheric aerosol model simulations in GA4 UM-UKCA of the Agung aerosol cloud (Dhomse et al., 2020) and new model experiments seeking to constrain the aerosol clouds from two VEI4 eruptions in Sep 1965 (Taal, Phillipines) and Aug 1966 (Awu, Indonesia).

The first global atmospheric model (WACCM-Al) of meteor-ablated aluminum was constructed from three components: the Whole Atmospheric Community Climate Model (WACCM6); a meteoric input function for Al derived by coupling an astronomical model of dust sources in the solar system with a chemical meteoric ablation model; and a comprehensive set of neutral, ion-molecule and photochemical reactions relevant to the chemistry of Al in the upper atmosphere. The reaction kinetics of two important reactions that control the rate at which Al+ ions are neutralized were first studied using a fast flow tube with pulsed laser ablation of an Al target, yielding k(AlO+ + CO) = (3.7 ± 1.1) × 10-10 and k(AlO+ + O) = (1.7 ± 0.7) × 10-10 cm3 molecule-1 s-1 at 294 K. The first attempt to observe AlO by lidar was made by probing the bandhead of the B2Σ+(v’ = 0) ← X2Σ+(v” = 0) transition at λair = 484.23 nm. An upper limit for AlO of 57 cm-3 was determined, which is consistent with a night-time concentration of ~5 cm-3 estimated from the decay of AlO following rocket-borne grenade releases. WACCM-Al predicts the following: AlO, AlOH and Al+ are the three major species above 80 km; the AlO layer at mid-latitudes peaks at 89 km with a half-width of ~5 km, and a peak density which increases from a night-time minimum of ~10 cm-3 to a daytime maximum of ~60 cm‑3; and that the best opportunity for observing AlO is at high latitudes during equinoctial twilight.

The widespread presence of meteoric smoke particles (MSPs) within a distinct class of stratospheric aerosol particles has become clear from in-situ measurements in the Arctic, Antarctic and at mid-latitudes. We apply an adapted version of the interactive stratosphere aerosol configuration of the composition-climate model UM-UKCA, to predict the global distribution of meteoric-sulphuric particles nucleated heterogeneously on MSP cores. We compare the UM-UKCA results to new MSP-sulphuric simulations with the European stratosphere-troposphere chemistry-aerosol modelling system IFS-CB05-BASCOE-GLOMAP. The simulations show a strong seasonal cycle in meteoric-sulphuric particle abundance results from the winter-time source of MSPs transported down into the stratosphere in the polar vortex. Coagulation during downward transport sees high latitude MSP concentrations reduce from ~500 per cm3 at 40km to ~20 per cm3 at 25km, the uppermost extent of the stratospheric aerosol particle layer (the Junge layer). Once within the Junge layer’s supersaturated environment, meteoric-sulphuric particles form readily on the MSP cores, growing to 50-70nm dry-diameter (Dp) at 20-25km. Further inter-particle coagulation between these non-volatile particles reduces their number to 1-5 per cc at 15-20km, particle sizes there larger, at Dp ~100nm. The model predicts meteoric-sulphurics in high-latitude winter comprise >90% of Dp > 10nm particles above 25km, reducing to ~40% at 20km, and ~10% at 15km. These non-volatile particle fractions are slightly less than measured from high-altitude aircraft in the lowermost Arctic stratosphere (Curtius et al., 2005; Weigel et al., 2014), and consistent with mid-latitude aircraft measurements of lower stratospheric aerosol composition (Murphy et al., 1998), total particle concentrations also matching in-situ balloon measurements from Wyoming (Campbell and Deshler, 2014). The MSP-sulphuric interactions also improve agreement with SAGE-II observed stratospheric aerosol extinction in the quiescent 1998-2002 period. Simulations with a factor-8-elevated MSP input form more Dp>10nm meteoric-sulphurics, but the increased number sees fewer growing to Dp ~100nm, the increased MSPs reducing the stratospheric aerosol layer’s light extinction.

Measurements from the Solar Occultation For Ice Experiment (SOFIE) are used to characterize meteoric smoke and meteor influx in both hemispheres. New smoke extinction retrievals from sunrise measurements in the Northern Hemisphere (NH) are presented, which complement the previously reported sunset observations in the Southern Hemisphere (SH). The sunrise observations are in good agreement with simulations from the Whole Atmosphere Community Climate Model (WACCM), for both the seasonal and height dependence of smoke in the mesosphere. The SOFIE - WACCM comparisons assumed that smoke in the mesosphere exists purely as Fe-rich olivine. This is justified because olivine is detected optically by SOFIE, it has the same elemental abundance as incoming meteoroids, and it is anticipated by theory and laboratory experiments. Treating mesospheric smoke as olivine furthermore brings closure in terms of the ablated and total meteoric influx determined here from SOFIE and a recent and independent investigation based on models and observations. SOFIE observations from 2007 - 2021 indicate a global ablated meteoric influx of 7.3 +/- 2.0 metric tons per day (t/d), which corresponds to a total influx (ablated plus surviving material) of 25.0 +/- 7.0 t/d. Finally, SOFIE indicates less smoke in the polar winter SH compared to NH winter. Finally, the results indicate stronger descent in the NH polar winter mesosphere than in the SH winter. This hemispheric asymmetry is indicated by smoke and water vapor results from both SOFIE and WACCM.