development of the cmaq-ucd sectional aerosol model k. max zhang and anthony s. wexler university of...
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Development of the Development of the CMAQ-UCD Sectional CMAQ-UCD Sectional
Aerosol ModelAerosol ModelK. Max Zhang and Anthony S. WexlerK. Max Zhang and Anthony S. Wexler University of California DavisUniversity of California Davis
Biosketch of CMAQ-Biosketch of CMAQ-UCDUCD
19919900
19919988
1999-1999-20002000
2002-2002-20032003
8:30pm (EST) Feb 9, 8:30pm (EST) Feb 9, 2005, Atlanta2005, Atlanta
Tony Wexler wrote the Tony Wexler wrote the original AIMoriginal AIM
Sun and Wexler Sun and Wexler simulated SCAQS simulated SCAQS particle size particle size distributionsdistributions
Clegg, Brimblecombe Clegg, Brimblecombe and Wexler and Wexler developed online AIMdeveloped online AIM
CMAQ-AIM in CMAQ-AIM in VISTASVISTAS
Started CMAQ-Started CMAQ-AIM effortAIM effort
Renamed to Renamed to CMAQ-UCDCMAQ-UCD
2004 - 2004 - presentpresent
CMAQ-AIM in BRACE, CMAQ-AIM in BRACE, CRPAQSCRPAQS
20062006CMAQ-UCD public CMAQ-UCD public releaserelease
• Uses Models-3/CMAQ as platformUses Models-3/CMAQ as platform• Incoporates an aerosol module developed Incoporates an aerosol module developed
by Sun, Zhang and Wexler.by Sun, Zhang and Wexler.• The aerosol module is sectional, fully The aerosol module is sectional, fully
dynamic and computationally efficient.dynamic and computationally efficient.
CMAQ-UCDCMAQ-UCD
Gas ChemistryGas Chemistry Aerosol DynamicsAerosol Dynamics
Integration of large set of Integration of large set of stiff ODEsstiff ODEs
the calculation of rate of the calculation of rate of change for gas-phase species change for gas-phase species is is mathematically trivial: mathematically trivial:
...21 RRi ckc
dtdc
requires requires partitioningpartitioning between between gaseous and particulate phasesgaseous and particulate phases
the calculation of rate of the calculation of rate of change for particulate species change for particulate species needs needs aerosol thermodynamicsaerosol thermodynamics computationcomputation
Gas-phase chemistry vs. Aerosol Gas-phase chemistry vs. Aerosol dynamicsdynamics
Dynamic Gas-to-Particle Dynamic Gas-to-Particle TransportTransport
• UncoupledUncoupled Partitioning of each volatile species one by onePartitioning of each volatile species one by one
• CoupledCoupled (near pH independent) (near pH independent) NHNH33 and HNO and HNO33 and/or NH and/or NH33 and HCl condense and and HCl condense and
evaporate together to maintain near acid-neutralityevaporate together to maintain near acid-neutrality
• ReplacementReplacement (near pH independent) (near pH independent) HNOHNO33 condenses as HCl evaporates or vice versa condenses as HCl evaporates or vice versa
in near acid-neutrality conditionsin near acid-neutrality conditions
HNOHNO33(g)(g)UncoupUncoupledled
Calculate vapor pressure Calculate vapor pressure of HNOof HNO33 and NH and NH33 on on particle surfaceparticle surface
NHNH33(g)(g)
NONO33--
Then partition NHThen partition NH33..
NHNH33(g)(g)UncoupUncoupledled
NHNH44++
NONO33--
UncoupUncoupledled
NHNH44NONO33
HNOHNO33(g)(g) NHNH33(g)(g)CoupleCoupledd
In near acid-neutrality In near acid-neutrality conditionsconditionsNHNH44NONO33
HNOHNO33(g)(g) HCl(g)HCl(g)ReplacemReplacementent
ClCl--NONO33-- In near acid-neutrality In near acid-neutrality
conditionsconditions
CaseCase TTAA TTNN TTCC Mechanism(s)Mechanism(s)11 No Aerosol ThermodynamicsNo Aerosol Thermodynamics
22 XX UncoupledUncoupled
33 XX UncoupledUncoupled
44 XX UncoupledUncoupled
55 XX XX Coupled NHCoupled NH33 and HNO and HNO33
66 XX XX Coupled NHCoupled NH33 and HCl and HCl
77 XX XX ReplacementReplacement
88 XX XX XX Coupled NHCoupled NH33 and HNO and HNO33, NH, NH33 and HCl and HCl
Simplified Simplified ThermodynamicsThermodynamics
• A rigorous approach is to minimize Gibbs A rigorous approach is to minimize Gibbs free energyfree energy
• What we need: equilibrium vapor pressures What we need: equilibrium vapor pressures of NHof NH33/HNO/HNO33/HCl, and water content /HCl, and water content (requiring (requiring phase state)phase state)
• Strategies:Strategies: Using phase diagrams to determine phase stateUsing phase diagrams to determine phase state Using vapor pressure cap to determine the Using vapor pressure cap to determine the existence of NHexistence of NH44NONO33(s) and NH(s) and NH44Cl(s)Cl(s)
Phase diagram of Phase diagram of HH++, NH, NH44++, SO, SO44
2-2-, NO, NO33--
2233 ANANANHNONH mKpp
ANHNONH Kpp 33
Vapor Pressure CapVapor Pressure Cap
ConstantConstant
MolalityMolality
Activity CoefficientActivity CoefficientVapor Vapor pressurepressure
0.1
1
10
100
PN
H3P
HN
O3
(ppb
2 )
0.90.80.70.60.50.4Relative Humdity
10-19
10-18
10-17
10-16
PN
H3 P
HN
O3 (atm
2)
10 oC
20 oC
30 oC
Numerical Integration Numerical Integration using ATSusing ATS
• We are developing an Asynchronous Time-We are developing an Asynchronous Time-Stepping (ATS) integration method.Stepping (ATS) integration method.
• Similar concepts have been applied in Similar concepts have been applied in molecule dynamics and solid mechanics.molecule dynamics and solid mechanics.
• With ATS, each variable is integrated based With ATS, each variable is integrated based on its intrinsic time scale.on its intrinsic time scale.
• CPU time can be saved by reducing number CPU time can be saved by reducing number of integrations for slow variables and of integrations for slow variables and avoiding inversion of large Jacobian. avoiding inversion of large Jacobian.
ε1c1
c2
c3
. . .
cn
tcurr tnew
ε2
ε3
εn
“pass”
“scan”……
……
……
……
……
. . .
t1,local
t2,local
t3,local
fastest
slowest
tn,local
ATS vs. GEAR for typical ATS vs. GEAR for typical TampaTampa conditions conditions
Condensation caseCondensation case Evaporation caseEvaporation case
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
RM
S
0.12 3 4 5 6
12 3 4 5 6
102 3
CPU time (s)
Gear ATS
(a)
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
RM
S
0.012 3 4 5 6
0.12 3 4 5 6
12
CPU time (s)
Gear ATS
(b)
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
RM
S
0.0012 3 4 5 6
0.012 3 4 5 6
0.12 3
CPU time (s)
Gear ATS
(c)
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
RM
S
0.0012 4 6 8
0.012 4 6 8
0.12 4
CPU time (s)
Gear ATS
(d)
ATS vs. GEAR for typical ATS vs. GEAR for typical BakersfieldBakersfield conditions conditions
Condensation caseCondensation case Evaporation caseEvaporation case
ATS vs. GEAR for typical ATS vs. GEAR for typical Los AngelesLos Angeles conditions conditions
Condensation caseCondensation case Evaporation caseEvaporation case
2
46
0.001
2
46
0.01
2
46
0.1
RM
S
0.1 1 10CPU time (s)
(e)
Gear ATS
10-6
10-5
10-4
10-3
10-2
RM
S
5 6 7 8 90.1
2 3 4 5 6 7 8 91
CPU time (s)
(f)
Gear ATS
ATS vs. GEAR for typical ATS vs. GEAR for typical RiversideRiverside conditions conditions
Condensation caseCondensation case Evaporation caseEvaporation case
2
3
456
0.01
2
3
4
RM
S
5 60.1
2 3 4 5 61
2 3 4 5 610
2
CPU time (s)
(g)
Gear ATS
68
0.001
2
4
68
0.01
2
4
68
0.1
RM
S
4 5 60.1
2 3 4 5 61
2 3 4 5 610
CPU time (s)
Gear ATS
(h)
ATS BenchmarkATS BenchmarkTest Test CasesCases
EPS = 0.1EPS = 0.1 EPS = 0.01EPS = 0.01
RMSRMSCPU CPU time time (s)(s)
RMSRMS CPU time CPU time (s)(s)
TampaTampa Cond.Cond. 4.74.71010-2-2 0.230.23 8.68.61010-4-4 0.470.47
Evap.Evap. 1.71.71010-2-2 0.040.04 1.31.31010-3-3 0.140.14
BakersfieBakersfieldld
Cond.Cond. 1.01.01010-2-2 0.00240.0024 1.31.31010-3-3 0.0130.013
Evap.Evap. 1.21.21010-2-2 0.00240.0024 5.85.81010-4-4 0.0190.019
Los Los AngelAngeleses
Cond.Cond. 4.34.31010-3-3 0.030.03 2.92.91010-3-3 0.140.14
Evap.Evap. 5.45.41010-3-3 0.050.05 1.11.11010-3-3 0.180.18
RiversideRiverside Cond.Cond. 8.08.01010-3-3 0.050.05 2.92.91010-3-3 0.180.18
Evap.Evap. 8.08.01010-3-3 0.040.04 3.63.61010-3-3 0.120.12
SDASDA 1.91.9 2.72.7
Summary• We developed a sectional, dynamic partitioning and We developed a sectional, dynamic partitioning and
computationally efficient aerosol module in CMAQ-computationally efficient aerosol module in CMAQ-UCD.UCD.
• CMAQ-UCD adopts three gas-to-particle partitioning CMAQ-UCD adopts three gas-to-particle partitioning schemes: Uncoupled, Coupled and Replacement.schemes: Uncoupled, Coupled and Replacement.
• CMAQ-UCD applies simplified thermodynamic CMAQ-UCD applies simplified thermodynamic schemes to determine the vapor pressures of volatile schemes to determine the vapor pressures of volatile species and particle phase states.species and particle phase states.
• CMAQ-UCD employs a novel asynchronous time-CMAQ-UCD employs a novel asynchronous time-stepping (ATS) integration technique to solve stiff stepping (ATS) integration technique to solve stiff ODE problems in aerosol dynamics.ODE problems in aerosol dynamics.
AcknowledgementAcknowledgement• USEPA• California Air Resources Board• VISTAS• Dr. Robin Dennis, Dr. Ajith Kaduwela and
Dr. Gail Tonnesen
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