Modelling U.K. Atmospheric Aerosol Using the CMAQ Models-3 Suite Michael Bane and Gordon McFiggans Centre for Atmospheric Science University of Manchester

© (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

© (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 built upon CMAQ v4.4  various options for mass transfer & equilibrium treatments

© (March 2007) Modal or Sectional? sectional representation of aerosol dynamics is more flexible

© (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 built upon CMAQ v4.4  various options for mass transfer & equilibrium treatments Recall CMAQ written in US for US legislation…

© (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

© (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 )

© (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…)

© (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

© (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

© (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

© (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

© (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

© (March 2007) Example comparison: 10:30-11:30 © Univ. of Manchester

© (March 2007) Nitrate Timeseries Standard CMAQ (modal) MADRID hybrid CIT equi with het chem (8 sectional) © Univ. of Manchester

© (March 2007) Sulphate Aerosol at Ground Layer © Univ. of Manchester

© (March 2007) Dry Deposition © Univ. of Manchester

© (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

© (March 2007) Mass differences in largest section at time of interest Scatter plot for mass in largest section ( micron) over all timesteps © Univ. of Manchester

© (March 2007) Mass-size & species composition at given cell at 09:00GMT on MADRID CMAQ © Univ. of Manchester

© (March 2007) Mass-size & species composition at given cell at 09:00GMT on MADRID CMAQ Too much mass in largest section © Univ. of Manchester

© (March 2007) Mass-size & species composition at given cell at 09:00GMT on MADRID CMAQ Mass shifted too far into Accumulation mode © Univ. of Manchester

© (March 2007) © Univ. of Manchester

© (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

© (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…

© (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?)

© (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