SOLAS Dust workshop (Reading) Overview of dust modelling from Leeds global aerosol group Graham Mann, Ken Carslaw, Dominick Spracklen, Hannele Korhonen, Joonas Merikanto, Maria Frontoso Paul Manktelow, Dave Ridley, Matt Woodhouse, Zongbo Shi, Mike Krom, Lianne Benning Institute for Climate & Atmospheric Science, School of Earth & Environment University of Leeds.

SOLAS Dust workshop (Reading) Several community global aerosol models developed at Leeds (soon available) TOMCAT global CTM GLOMAP-bin aerosol module (sectional aerosol) Unified Model HadGEM climate model QUEST Earth System Model Observations Field campaigns APPRAISE Community Model Climate Prediction GLOMAP-bin (no. & mass conc. in size bins) The most complete aerosol scheme that can be run globally GLOMAP-mode (no. & mass conc. in log-normal modes) A reduced GLOMAP, cheap enough to run in the UKCA composition-climate model & coupled to Earth System. The Global Model of Aerosol Processes (GLOMAP) was developed in Leeds to model aerosol microphysics & chemistry with detailed size-resolved composition. 2 aerosol schemes GLOMAP-mode aerosol module (modal aerosol) or GLOMAP-mode aerosol module (modal aerosol) UKCA Community Model Schemes in 3 model environments 1) chemical transport model (TOMCAT) 2) nested to particular region in CTM 3) coupled to climate in GCM (UM)

SOLAS Dust workshop (Reading) Number size distributions from GLOMAP-bin & GLOMAP-mode (annual mean) GLOMAP-mode GLOMAP-bin Arctic N. Atlantic Sub-tropics Tropics Southern Ocean Antarctic Modal scheme (as implemented into UKCA) matches the number size distributions from the more detailed GLOMAP-bin scheme remarkably well. Some discrepancies in coarse mode mode overestimates (sedimentation?).

SOLAS Dust workshop (Reading) GLOMAP-bin & -mode being tested against 20 years of published observations Spracklen et al. (2005) microphysical models…to understand the factors that control the number of CCN at a given supersaturation

SOLAS Dust workshop (Reading) GLOMAP CCN against in-situ observations GLOMAP-bin GLOMAP-mode Both models compare fairly well against observations but both tend to underestimate at high CCN numbers new particle formation in BL not included.

SOLAS Dust workshop (Reading) Dust emissions scheme used in GLOMAP include in UKCA Size distribution of dust emissions is a key uncertainty in dust modelling and is critical for the climate impact of dust. Smallest dust particles (<1 m) have long lifetimes and are the most important particles with respect to climate. Have implemented scheme of Alfaro & Gomez (2001) which represents the physics of the sand-blasting process. Experiments in a wind tunnel (Alfaro et al, 1998) showed that saltating aggregates impacting on surface dust release smaller sized particles only in stronger wind events mode 1 (14.2 m mass median diameter) mode 2 (6.7 m mass median diameter) mode 3 (1.5 m mass median diameter) Modes only released once binding energies exceeded by energy of saltating aggregates. Small modes have larger binding energies (more energy required)

SOLAS Dust workshop (Reading) GLOMAP-bin (A&G) dust against Univ. Miami observations mass ( gm -3 ) Annual mean surface dust concentration Global surface fields of soil moisture, leaf area index, snow/ice cover & preferential source areas [paleolake beds] from Tegen et al (2002) determine horizontal saltation flux ISLSCP global soil texture dataset drives size distribution of saltating aggregates Influence of particle size and soil moisture on threshold friction velocity following Woodward (2001) From Manktelow PhD thesis.

SOLAS Dust workshop (Reading) GLOMAP-bin (A&G) mass conc. vs observations Overestimates at some remote sites Underestimates near source Annual mean Modelled spatial dust mass distribution in reasonable agreement with observations (log correlation coefficient of 0.8). Captures timing of Asian dust maximum (not shown). From Manktelow PhD thesis.

SOLAS Dust workshop (Reading) GLOMAP 2-mode vs 7-bin representation of dust transport GLOMAP-mode run using 2 size modes (4 tracers) GLOMAP-bin run using 7 dust bins (14 tracers) Here both use prescribed daily dust emission fluxes for AEROCOM by Paul Ginoux (GFDL) Use GLOMAP-mode and –bin driven by Alfaro & Gomez sandblasting scheme for predicting dust deposition to ocean over several years. Collaboration with UEA (Le Quere, Buitenhuis) to model ecosystem response Shift in size distribution examined at 8 sites going out from Sahara over ocean.

SOLAS Dust workshop (Reading) Influence of dust on sulphate aerosol Some studies (e.g. Bauer & Koch, 2005) have found large enhancements of sulphate due to heterogeneous oxidation of SO2 on dust. Despite high concentrations of dust in ACE-Asia Perfect Dust Storm, GLOMAP-bin sulphate still not significantly enhanced due to quenching of sites for oxidation once dust particles are aged (Manktelow, PhD thesis). However, mixing of dust with pollution affects particle lifetime, hygroscopicity & solubility SO4 ( gm -3 ) % increase

SOLAS Dust workshop (Reading) Size-dependence of dust deposition processes also important Need to test deposition of GLOMAP modal dust and coarse bin schemes to see how they perform against bin-resolved schemes with large number of bins.

SOLAS Dust workshop (Reading) GLOMAP dust deposition to ocean using A&G vs DIRTMAP Generally encouraging spatial distribution of dust deposition vs observations Sandblasting scheme seems to give too short a lifetime too low deposition. Not enough smaller particles with longer lifetimes but this could be enhanced by sub-grid wind speed variability causing more smaller particles to be ejected Marine sediment trap measurements of dust deposition as compiled by Tegen et al (2002) Deposition to ocean provides nutrients to ocean phytoplankton Dust deposition (gm -2 yr -1 ) From Manktelow PhD thesis.

SOLAS Dust workshop (Reading) SOLAS KT project on dust deposition & DMS emissions DMS production in high-nutrient low-chlorophyl areas of the ocean can be stimulated by dust-deposition as a result of Fe limitation. Consequent increase in CCN and uptake of CO 2 Uptake of acids and cycling through clouds affect Fe solubility & bio-availibility Matt Woodhouse, Graham Mann, Ken Carslaw (University of Leeds)

SOLAS Dust workshop (Reading) GLOMAP-mode 2xDMS patch experiments show CCN impact is not local. CCN change <2% in perturbed patch CCN changes seen far from patch

SOLAS Dust workshop (Reading) SOLAS project – factors controlling dust bioavailability When rocks containing iron minerals weather under desert conditions they tend to produce chemically refractory iron oxides (haemetite and goethite). When dust is taken up into the atmosphere it interacts with acid in clouds. The cloud processes may convert the refractory iron into dissolved Fe. When the dissolved Fe reprecipitates we suggest it does so as chemically reactive Fe nanoparticles Mike Krom, Zongbo Shi, Lianne Benning, Ken Carslaw, Graham Mann, Alex Baker, Tim Jickells (University of Leeds and University of East Anglia)

SOLAS Dust workshop (Reading) What we are going to do? Carry out controlled lab experiments using realistic simulated atmospheric conditions to determine the fraction of unreactive Fe converted to Fe nanoparticles. Examine dust samples collected in SOLAS cruises using modern microscopic and spectroscopic techniques with conventional methods and relate this to measures of Fe solubility. Use a global model of aerosol processes from UKCA which will be evaluated against the available and new/ongoing understandings of processes. Understand the contribution of physical size sorting and chemical processing of dust particles towards changing the solubility & bioavailability of iron

SOLAS Dust workshop (Reading) Summary Range of environmental applications involving global modelling of dust aerosol to be carried out at Leeds with GLOMAP, UKCA and QUEST models. Climate impacts of dust via direct radiative effect (UKCA) Impact on aerosol & climate feedbacks from enhanced DMS by large-scale dust deposition (SOLAS KT PhD) Impact of dust deposition to oceans on marine ecosystem (QUEST ESM & collaboration with UEA) Chemical transformation of dust during transport and impact on bioavailibility to ocean ecosystem (SOLAS) Impact of dust on sulphate aerosol properties and interaction with other aerosol components

SOLAS Dust workshop (Reading) The influence of DMS on CCN concentrations at Cape Grim Around 50% of CCN at Cape Grim in SH winter caused by sulfate particles from enhanced new particle formation as a result of DMS from phytoplankton (Korhonen et al., in preparation) Observed Model Model, no DMS

SOLAS Dust workshop (Reading) Standard UKCA Aerosol Scheme Mode nameMean rad range nm CompositionProductionComments nucleation soluble < 5SO4nucleationCurrently only binary H 2 SO 4 -H 2 O, later BLN Aitken insoluble 5 – 50BC, OCprimary BC/OC emissionsSeparation to handle BC/OC ageing (necessary if timescale for ageing > lifetime in grid box) Aitken soluble 5 – 50SO4, BC, OCgrowth of nucl. soluble, condensation (sol,ins Ait), primary SO4 ems, coag. Accum. insoluble 50 – 500DUprimary DU emissionsSeparation to handle dust ageing (as above Primary accum. mode BC/OC ageing? Accum. soluble 50 – 500SO4, SS, DU, BC, OC growth of Aitken soluble, condensation (sol,ins acc) primary SS ems, coag. Coarse insoluble >500DUprimary DU emissionsSeparation to handle dust ageing Coarse soluble >500SO4, SS, DU, BC?, OC? growth of accum soluble, primary SS emission Equates to advected aerosol tracers

SOLAS Dust workshop (Reading) Observed and modelled nucleation events Observed (using 2 DMPSs) GLOMAP -bin modelled (using BL nucleation paramn) See Spracklen et al (2006) GLOMAP simulates observed nucleation bursts at Hyytiala remarkably well given that it is from a global model run.

SOLAS Dust workshop (Reading) Impact of including BL nucleation on CCN concentrations. Absolute change Baseline CCN We find that BL nucleation has a significant impact on regional CCN, Spracklen et al.(2006) Spracklen et al (submitted 2007)

SOLAS Dust workshop (Reading) GLOMAP & UKCA simulate internal mixtures and ageing of aerosol SO4 BC OC Sea salt Coagulation CCN Primary BC/OC distribution (assumed insoluble) SOA & H 2 SO 4 Condensation of Ageing 1 monolayer Two simulations with and without condensation ageing Condensation and chemical reaction Insoluble More solublePartially soluble

SOLAS Dust workshop (Reading) Impact of particle ageing on model CCN against observations BC/OC condensation aged BC/OC not condensation aged S Africa, SAFARI-2000 Probably not aged Korea, Germany, Amazon Aged particles can act as CCN Particle chemical ageing is fundamentally important for climate change (it can change CCN by a factor 10)

SOLAS Dust workshop (Reading) Changes in global & regional sulfate aerosol since the 1980s. Considering annual regional burdens, find: 1% reduction in European SO 2 emissions. 0.65% decrease in regional SO4 burden 1% increase in E. Asian SO 2 emissions 0.88% increase in regional SO4 burden Stronger oxidant limitation in-cloud over Europe & N. America compared to S. Asia & E. Asia means 12% decrease in global SO 2 emissions resulted in only a 3% decrease in global SO 4 aerosol burden. -4mgS m mgS m -2 +6mgS m -2 -2mgS m -2 -4mgS m -2 +5mgS m -2 see Manktelow et al (2007) SO2 emissions SO4 production dry oxdn wet oxdn

SOLAS Dust workshop (Reading) Summary & conclusions A number of global aerosol models based on GLOMAP have been developed at Leeds & will soon be available as community models in CTM (offline) and GCM (coupled) frameworks. GLOMAP-bin is a detailed bin-resolved model for short timescales. GLOMAP-mode is a reduced version for longer integrations and for GCM simulations coupled to atmospheric dynamics and clouds. The UKCA sub-model now has GLOMAP-mode incorporated in the UM environment (although not yet coupled to radiation & clouds). A nested version of GLOMAP will enable high-resolution simulations of regional aerosol including long-range transport and other important global impacts (e.g. FT nucleation). The models are being used for a variety of applications including new particle formation, biomass burning, air quality, volcanic aerosol, dust-chemistry & DMS-CCN Earth System interactions.

SOLAS Dust workshop (Reading) CN & CCN from GLOMAP-bin & GLOMAP-mode (December 2000) GLOMAP-bin surface CN (cm -3 ) GLOMAP-bin surface CCN (cm -3 ) GLOMAP-mode surface CCN (cm -3 ) GLOMAP-mode surface CN (cm -3 )

SOLAS Dust workshop (Reading) Number size distributions from GLOMAP-bin & GLOMAP-mode (December 2000) GLOMAP-mode GLOMAP-bin Modal scheme (as implemented into UKCA) reproduces the number size distributions from the more detailed GLOMAP-bin scheme quite well. Some discrepancies in nucleation & Aitken modes. Arctic N. Atlantic Sub-tropics Tropics Southern Ocean Antarctic