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Lower tropospheric COS as main source of stratospheric background aerosol, a CCM study Christoph Brühl (1), Holger Tost (2), Paul Crutzen (1), Jos Lelieveld.

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Presentation on theme: "Lower tropospheric COS as main source of stratospheric background aerosol, a CCM study Christoph Brühl (1), Holger Tost (2), Paul Crutzen (1), Jos Lelieveld."— Presentation transcript:

1 Lower tropospheric COS as main source of stratospheric background aerosol, a CCM study Christoph Brühl (1), Holger Tost (2), Paul Crutzen (1), Jos Lelieveld (1), and Francois Benduhn (1) (1) Max-Planck-Institut für Chemie, Mainz, Germany, (2) Universität Mainz, Germany Abstract: The modular atmospheric chemistry circulation model EMAC with the aerosol module gmxe and high vertical resolution has been used for multiyear simulations of atmospheric aerosol. As lower boundary condition observed concentrations of COS and other long lived source gases are used, together with emissions of shorter lived gas and aerosol species. The parameters for the aerosol size distribution in the 7 modes are the same for troposphere and middle atmosphere. Evaporation of sulfate particles in the middle atmosphere is taken into account. We show that the oxidation of COS transported into the stratosphere explains most of the stratospheric background aerosol (Junge layer) and SO 2 observed by satellites (SAGE, Space Shuttle), including the modulation by the (internally calculated) Quasi-Biennial Oscillation. Tropospheric SO 2 has a minimum below the tropopause due to scavenging and cannot be a large contribution to stratospheric sulfur. We show also, that the model is able to build up the aerosol from a volcanic SO 2 injection, and discuss some radiation effects. For both, the background, and the volcanic aerosol, the sedimentation is critical. The model EMAC (ECHAM5/MESSy Atmos.Chem. circulation model), ATF-version 1.9 (Jöckel et al, 2006; Pringle et al, 2010) Resolution T42/L90 and T31/L39 (to 1Pa), up to 7 years Mecca1 chemistry module, modified + GMXe aerosol module (4 soluable and 3 unsoluable modes with eqsam) + scav (cloud chemistry) In mecca1 extended SOx gas phase chemistry with HS, S, SO, SO 2, SO 3 In GMXe evaporation of sulfate particles added using Vehkamäki vapor pressure formula (essential to avoid particles in upper stratosphere), mode change due to shrinking possible; optical properties diagnosed. Modes: Nucleation < 6nm < Aitken < 70nm < Accumulation < 1000nm < Coarse (r) (sigma) Photolysis of H 2 SO 4 and SO 2 in UV and visible (vibrational overtones) included PSCs included, with sulfate sedimentation in solid particles Long lived tracers including COS nudged to observations at surface (Montzka and ALE/GAGE) Internally calculated QBO, consistent with observations Optical properties of aerosol from lookup-table (Mie based) More see References: Jöckel et al., The atmospheric chemistry general circulation model ECHAM5/MESSy1: consistent simulation of ozone from the surface to the mesosphere. Atmos.Chem.Phys. 6, , Pringle et al., Description and evaluation of GMXe: a new aerosol submodel for global simulations (v1). Geosci.Model Dev.. 3, , Vehkamäki et al., An improved parameterization for sulfuric acid–water nucleation rates for tropospheric and stratospheric conditions. J.Geoph.Res. 107, D22, 4622, Production of total anorganic sulfur from oxidation of COS (proposed first by Crutzen, 1976) QBO west to east (1999) QBO east to west (2000) COS, observed by ACE satellite (Barkley et al, 2008, corresponding season and QBO) References: Barkley et al, Global distributions of carbonyl sulfide in the upper troposphere and stratosphere, Geoph.Res.Lett. 35, L14810, Crutzen, The possible importance of CSO for the sulphate layer of the stratosphere. Geophys.Res.Lett. 3, 73-76, Watts, The mass budgets of carbonyl sulfide…, Atm.Environ. 34, , EMAC Altitude, km Altitude, km SOx, and total S, ppbv. Observed by ATMOS on Spacelab 3 at 1hPa about 0.1ppbv SO 2 (Rinsland et al, 1995, Geoph.Res.Lett.) Particulate sulfate, ppbv. Black contours: Derived from SAGE observations Grey contours: Zonal wind (QBO, m/s): -30, -10E, +10, +30W Modif. Walcek sedimentation Trapezoid sedimentation Background aerosol, Junge layer (after 3years of spinup from zero sulfur in the middle atmosphere) log(p/hPa) Sulfate, ppbv, April Black contours: SAGE fitting to QBO, grey: fitting to season. Tropical pipe better reproduced with (modified) Walcek sedimentation scheme log(p/hPa) Trapezoid Walcek Observed SO 2 by ATMOS on Spaceshuttle in March 92 at 1hPa 0.4ppbv (Rinsland et al 1995) Mostly via gaseous H 2 SO 4 and subsequent photolysis Pinatubo volcanic aerosol, ppbv (log), injection of SO 2 at 1 Sept, different sedimentation schemes and resolution, 1°N Conclusions Oxidation of COS explains most of the stratospheric Junge layer (about 75%) and stratospheric SO 2, as observed. The stratospheric aerosol layer builds up in about 1 year if initialized from zero. The Quasi-Biennual-Oscillation of the zonal wind modulates the Junge layer in EMAC, in agreement with satellite data Calculated extinctions agree with satellite data if Mie calculations are consistent with size distribution parameters. Aerosol radiative heating rates are simulated realistically. In the lowermost stratosphere aerosol water, dust and organic carbon are also important for radiative effects. It is possible to use the 7-mode scheme for troposphere and stratosphere applying the same parameters, including volcanic aerosol (here decay somewhat too fast in the first year). To obtain optimal agreement with observed SO 2 in the upper stratosphere, the use of a sedimentation scheme with small numerical diffusion is important (e.q. modified Walcek); resolution also matters. L39/T31, modified WalcekL90/T42 modif. WalcekSAGE observationsL90/T42, trapezoidL39/T31, upwind Numerical diffusion Sulfate Aitken-mode, soluableAccumulation-mode, soluable N, 1/cm³ r, µm log(p/hPa) EMACSAGE (WMO) Extinction at 1µm, 1/km (log) Extinction, 1/km, at equator Heating rates, K/d, at equator Reference: WMO, SPARC Assessment of Stratospheric Aerosol Properties, WRCP-124, 2006 SOx, 1°N SAGE observationsEMAC COS sources sinks(Mt/yr) Ocean0.30+/-0.25 Oxic soils1.05+/-0.36 DMS ox0.17+/-0.04 Vegetation0.56+/-0.10 CS2 ox0.42+/-0.12Photochem 0.18+/-0.03 Anthrop /-0.06 Biom.B /-0.05 Precip.0.13+/-0.08 Watts (2000) Other0.10+/-0.08 Montzka Best agreement with Walcek and L90/T42 Maximum shifted to higher layers Modif. Walcek sedimentation


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