Modelling U.K. Atmospheric Aerosol Using the CMAQ Models-3 Suite Michael Bane and Gordon McFiggans...
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Transcript of 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
© [email protected] (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
© [email protected] (March 2007)
Modal or Sectional?
sectional
representation of
aerosol dynamics is
more flexible
© [email protected] (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…
© [email protected] (March 2007)
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
© [email protected] (March 2007)
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)
© [email protected] (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 2.5o x 2.5o
2007: moving to UM output (more later…)
© [email protected] (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
© [email protected] (March 2007)
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
© [email protected] (March 2007)
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
© [email protected] (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
© [email protected] (March 2007)
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:
© Univ. of Manchester
© [email protected] (March 2007)
Example comparison: 10:30-11:30
© Univ. of Manchester
© Univ. of Manchester
© [email protected] (March 2007)
Nitrate Timeseries
StandardCMAQ(modal)
MADRIDhybrid CITequi with het chem(8 sectional)
© Univ. of Manchester
© Univ. of Manchester
© [email protected] (March 2007)
Sulphate Aerosol at Ground Layer
© Univ. of Manchester © Univ. of Manchester
© [email protected] (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 © Univ. of Manchester
© [email protected] (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
© Univ. of Manchester
© [email protected] (March 2007)
Mass-size & species composition at given cell at 09:00GMT on 2005 140
MADRID
CMAQ
© Univ. of Manchester
© Univ. of Manchester
© [email protected] (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
© Univ. of Manchester
© [email protected] (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
© Univ. of Manchester
© [email protected] (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
© [email protected] (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…
© [email protected] (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?)
© [email protected] (March 2007)
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