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Modelling U.K. Atmospheric Aerosol Using the CMAQ Models-3 Suite Michael Bane and Gordon McFiggans Centre for Atmospheric Science University of Manchester
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© michael.bane@manchester.ac.uk (March 2007) Requirements for Aerosol Transport Model Necessity to interpret aerosol process research in light of aircraft (etc) measurements – what we require from a model: Framework for testing process descriptions eg equilibrium properties Prediction of Aerosol Field Measurements Size distributions Component loading by size Operational Model Future fieldwork planning & real time deployment
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© michael.bane@manchester.ac.uk (March 2007) Review: Aerosol Treatment in Models-3 Modal (“standard” CMAQ) version 4.6 released very recently (Oct 2006) Sectional (MADRID) model of aerosol dynamics, reaction, ionisation and dissolution “development” release 2004 - built upon CMAQ v4.4 various options for mass transfer & equilibrium treatments
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© michael.bane@manchester.ac.uk (March 2007) Modal or Sectional? sectional representation of aerosol dynamics is more flexible
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© michael.bane@manchester.ac.uk (March 2007) Review: Aerosol Treatment in Models-3 Modal (“standard” CMAQ) version 4.6 released very recently (Oct 2006) Sectional (MADRID) model of aerosol dynamics, reaction, ionisation and dissolution “development” release 2004 - built upon CMAQ v4.4 various options for mass transfer & equilibrium treatments Recall CMAQ written in US for US legislation…
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© michael.bane@manchester.ac.uk (March 2007) Set up: Emissions, IC, BC Standard CMAQ (modal) Emissions: 1999 EMEP (50km res, Europe), NAEI (1km res, UK)… gridded according to chemical mechanism (RADM2) IC, BC profiles for outer 108km domain
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© michael.bane@manchester.ac.uk (March 2007) Set up: Emissions, IC, BC Standard CMAQ (modal) Emissions: 1999 EMEP (50km res, Europe), NAEI (1km res, UK)… gridded according to chemical mechanism (RADM2) IC, BC profiles for outer 108km domain MADRID (sectional) Sectional emissions as per MADRID pre-processors (SCAQS, Aug 1987) Size & composition disaggregated from PM2.5 & PM10 IC, BC profiles for 108km domain: “import” CMAQ values into MADRID Reapportion (eg) sulphate Aitken & Accumulation mode masses into sectional representation (using CMAQ’s logNormal parameters) Ongoing ATMOS work Better size- & species- resolution of PM emissions and IC / BC for the UK from UK measurements ( e.g. from AMPEP flights & NCAS/DIAC work )
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© michael.bane@manchester.ac.uk (March 2007) Set-up: Domains, chemistry schemes, met Domains 108km 36km 12km 9 days’ spin up (too much?) Configuration Radm2 with isoprene (4 product) chem, aerosol & aqueous CMAQ: radm2_ci4_ae3_aq MADRID: radm2_ci4_aqRADM_aeMADRID1_8sec Rosenbrock solver (ros3) Met generated using MM5 and ECMWF gridded 2.5 o x 2.5 o 2007: moving to UM output (more later…)
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© michael.bane@manchester.ac.uk (March 2007) Aerosol At Manchester, our expertise is in modelling aerosol. Do standard CMAQ and MADRID model UK aerosol adequately? Can we incorporate Manchester’s new models into Models-3? Computational cost Increased accuracy Suitable parameterisations
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© michael.bane@manchester.ac.uk (March 2007) Assessing most useful representation Remove non-aerosol discrepancies between versions (one example): N2O5: CMAQ includes N 2 O 5 heterogeneous hydrolysis within aerosol routines; MADRID does not represent uptake dependence on aerosol nitrate (CMAQ uses N2O5 as function of nitrate loading) © Univ. of Manchester
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© michael.bane@manchester.ac.uk (March 2007) Comparison of Photochemistry Scatter plot of MADRID.v. CMAQ Ozone concentrations at 1200GMT 25 May 2005 (684 th timestep of 108 km domain) © Univ. of Manchester
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© michael.bane@manchester.ac.uk (March 2007) Gas/particle Mass Transfer Important aerosol process Condensation (evaporation) onto aerosol Dependent on: difference in partial pressure of gas and aerosol Size of particle (larger particles take longer to reach equilibrium) How treated? CMAQ [subroutine eql3()] Assumes aerosol totally aqueous (ISORROPIA metastable) Determines nitrate (etc) condensed to Ait & Acc modes, in proportion to sulphate mass distribution MADRID choices Bulk equilibrium: “fullCIT”, “hybridCIT” ie presumes “instanteous” equilibrium and use “correction factor” to distribute over sections (dependent on sulphate distribute or growth law dependent on particle size) Hybrid (small: bulk equilibrium; large: dynamic): “hybrid CMU” »Looked at bulk equilibrium & at 2 largest (>2.15micron) as dynamic »Dynamic: much more expensive, gives less mass in largest sections (as expected) All allow condensation to all sections
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© michael.bane@manchester.ac.uk (March 2007) Comparison with Aircraft Measurements Exploring how Models-3 (standard CMAQ & MADRID) predicts measurements BAe 146 Flights 2005 / 6, focus on B097, AMPEP Anticlockwise, May 2005, (S) Westerlies Aerodyne AMS 07:48 10:25 11:50 09:45 NB: altitude of flight varies greatly: © Univ. of Manchester
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© michael.bane@manchester.ac.uk (March 2007) Example comparison: 10:30-11:30 © Univ. of Manchester
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© michael.bane@manchester.ac.uk (March 2007) Nitrate Timeseries Standard CMAQ (modal) MADRID hybrid CIT equi with het chem (8 sectional) © Univ. of Manchester
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© michael.bane@manchester.ac.uk (March 2007) Sulphate Aerosol at Ground Layer © Univ. of Manchester
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© michael.bane@manchester.ac.uk (March 2007) Dry Deposition © Univ. of Manchester
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© michael.bane@manchester.ac.uk (March 2007) Compare mass-size distributions CMAQ only has sulphate in Aitken and Accumulation modes – nothing in the Coarse mode. This limits the amount of aerosol mass in largest sections – exactly those sections that will have highest rates of deposition. No such limitation exists for sectional MADRID. © Univ. of Manchester
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© michael.bane@manchester.ac.uk (March 2007) Mass differences in largest section at time of interest Scatter plot for mass in largest section (4.64-10micron) over all timesteps © Univ. of Manchester
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© michael.bane@manchester.ac.uk (March 2007) Mass-size & species composition at given cell at 09:00GMT on 2005 140 MADRID CMAQ © Univ. of Manchester
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© michael.bane@manchester.ac.uk (March 2007) Mass-size & species composition at given cell at 09:00GMT on 2005 140 MADRID CMAQ Too much mass in largest section © Univ. of Manchester
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© michael.bane@manchester.ac.uk (March 2007) Mass-size & species composition at given cell at 09:00GMT on 2005 140 MADRID CMAQ Mass shifted too far into Accumulation mode © Univ. of Manchester
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© michael.bane@manchester.ac.uk (March 2007) © Univ. of Manchester
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© michael.bane@manchester.ac.uk (March 2007) Comparisons of Gas-Particle Mass Transfer CMU hybrid: Some sections treated dynamically (MADM) – each iteration calls ISORROPIA (not cheap) Needed to correct code to check for and deal with convergence of ODEs If no convergence then use bulk equilibrium for all sections Other sections (small particles) can assume bulk equilibrium No dynamic sections Very similar results to CIT method (as expected: both bulk equilibrium) 2 dynamic sections Computation time rises dramatically <1% non-convergence Results need statistical analysis but appear to show that slightly less mass is put into the larger (dynamic) sections
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© michael.bane@manchester.ac.uk (March 2007) Also looked at… Setting ammonia emissions to zero Some US developers of MADRID have noted problems in ammonia rich regimes More likely in UK due to flue gas desulphurisation & other legislation Results need analysing…
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© michael.bane@manchester.ac.uk (March 2007) Aerosol in Models-3 Summary MADRID’s sectional approach gives more info CMAQ unrealistic: doesn’t allow growth into coarse mode Both CMAQ and MADRID seem to have shifted aerosol to unrealistically high sizes (possibly a US issue?)
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© michael.bane@manchester.ac.uk (March 2007) Conclusions; Ongoing/Future Work Conclusions Models-3 is suitable framework for advancing our understanding of aerosol processes & analysing measurements A sectional approach seems more suitable than a modal approach Ongoing/Future work Firmly establish suitability of MADRID Continue to investigate mass-size issue More detailed comparisons: additional aerosol species and flights; also ground-based measurements Use of Met Office UM & UM-MCIP (BADC archive; running PUM) Better emissions: UK size-resolved segregation (and more recent emissions) from ongoing NCAS work Improving MADRID Improve treatment of heterogeneous chemistry Use kinetic gas/particle dis-equilibrium mass transfer Improve SOA treatment Increase # sections within MADRID Use improved chemistry schemes (RADM2 no longer supported) Use model in operational mode
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