Modelling U.K. Atmospheric Aerosol Using the CMAQ Models-3 Suite Michael Bane and Gordon McFiggans...

Modelling U.K. Atmospheric Aerosol Using the

CMAQ Models-3 Suite

Michael Bane and Gordon McFiggans

Centre for Atmospheric Science

University of Manchester

© [email protected] (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


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


Modal or Sectional?

sectional

representation of

aerosol dynamics is

more flexible


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…


Set up: Emissions, IC, BCStandard 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


Set up: Emissions, IC, BCStandard 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)


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 2.5o x 2.5o

2007: moving to UM output (more later…)


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


Assessing most useful representationRemove non-aerosol discrepancies between

versions (one example):N2O5: CMAQ includes N2O5 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 © Univ. of Manchester


Comparison of Photochemistry

Scatter plot of MADRID .v. CMAQ Ozone concentrations at 1200GMT 25 May 2005 (684th timestep of 108 km domain)

© Univ. of Manchester


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


Comparison with Aircraft MeasurementsExploring 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

09:45NB: altitude of flight varies greatly:



Example comparison: 10:30-11:30




Nitrate Timeseries

StandardCMAQ(modal)

MADRIDhybrid CITequi with het chem(8 sectional)




Sulphate Aerosol at Ground Layer

© Univ. of Manchester © Univ. of Manchester


Dry Deposition



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.



Mass differences in largest section at time of interest

Scatter plot for mass in largest section (4.64-10micron)over all timesteps




Mass-size & species composition at given cell at 09:00GMT on 2005 140

MADRID

CMAQ





MADRID

CMAQ

Too much mass in largest section





MADRID

CMAQ Mass shifted too far into Accumulation

mode






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


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…


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?)


Conclusions; Ongoing/Future WorkConclusions

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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Modelling U.K. Atmospheric Aerosol Using the CMAQ Models-3 Suite Michael Bane and Gordon McFiggans...

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