evaluation of emission control strategies for regional scale air quality: performance of direct and...
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Evaluation of Emission Control Strategies for Regional Scale Air Quality:
Performance of Direct and Surrogate Techniques
Presented at the 6th Annual CMAS Conference Friday Center, UNC-Chapel Hill
October 1-3, 2007
Computational Chemodynamics Laboratory (CCL)Environmental and Occupational Health Sciences Institute (EOHSI)
A Joint Institute of UMDNJ-RW Johnson Medical School and Rutgers University170 Frelinghuysen Road, Piscataway, NJ 08854
*Atmospheric Sciences Modeling Division, Air Resources Laboratory, NOAA in partnership with the USEPA
S. Isukapalli, S. Wang, S. Napalenok* T. Kindap, and P. Georgopoulos
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Acknowledgments
• Alper Unal, WRI• Talat Odman and Yongtao Hu, Georgia Institute of Technology• USEPA (Funding for Center for Exposure and Risk Modeling)• NJDEP (Base funding for the Ozone Research Center)
• OTC Modeling Group Centers (Emissions inventories, Meteorology, etc.)
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Overview
• Surrogate Modeling Techniques • HDMR• DDM• Automatic Differentiation• Response Surface Modeling
• Case Study• Emissions and Regions• Estimates vs Brute Force
• Results and Discussion
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Use of surrogate models for emission control analysis
• Emissions control analysis is a multi-dimensional problem• Geographic regions [states/counties, etc.]• Types of emissions [point, biogenic, area, mobile, etc.] • Primary emissions [NOx, VOC, etc.]
• Some times, multi-objective problems
• Ozone, PM2.5, etc.
• Direct model simulation is expensive• 2 hours/day for OTC-12 domain simulation (8 Opteron nodes)
• Surrogate models can provide significant speedups• Construction of surrogate models is often parallelizable
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Use of surrogate models for emission control analysis
• Can provide a “Fast Equivalent Operational Model” (FEOM)• Can also be used in Uncertainty Propagation
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Use of surrogate models for emission control analysis
Several techniques exist for surrogate modeling• Response Surface Methods (Deterministic and Stochastic)• High Dimensional Model Representations (HDMR)• Local Gradient-Based Methods
•Decoupled Direct Method (DDM)•Adjoint Sensitivity Analysis Method•Automatic Differentiation
Features• Black-box models (Response Surface; HDMR; etc.)• Some changes to code (Automatic Differentiation)• Extensive changes to model code/new modules (DDM; Adjoint
Sensitivity)
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High Dimensional Model Representation (HDMR)
• System (a mathematical model; e.g. CMAQ):- Input I:- Output O:
• HDMR expresses model outputs as expansions of correlated functions:
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•The expressions of HDMR component functions are optimal choices for the output f (x) over the desired domain of the input variable space such that the HDMR expansion converges very rapidly
•Cut-HDMR:
• In practice, the HDMR expansion functions are represented as a set of low dimensional look-up tables
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•Decomposition of variance:
•The total variance 2(g) attributable to all inputs can be decomposed into individual contributions
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Automatic Differentiation (www.autodiff.org)
y(1) = 1.0 y(2) = 1.0 do i = 1,n if (x(i) > 0.0) then y(1) = x(i) * y(1) * y(1) else y(2) = x(i) * y(2) * y(2) endif enddo
dy(1) = 0.0 y(1) = 1.0 dy(2) = 0.0 y(2) = 1.0 do i = 1,n if (x(i) > 0.0) then dtemp = y(1)*dx(i) + x(i)*dy(1) temp = x(i) * y(1) dy(1) = y(1)*dtemp + temp*dy(1) y(1) = temp * y(1) else dtemp = y(2)*dx(i) + x(i)*dy(2) temp = x(i) * y(2) dy(2) = y(2)*dtemp + temp*dy(2) y(2) = temp * y(2) endif enddo
Chain Rule on Computer Instructions
Problems:ADIFOR does not support
F90/F95Commercial tools unproven
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Decoupled Direct Method (DDM)
• CMAQ-DDM 4.5 with CB4, Aero4, AQ • Serial version from Talat Odman, Georgia Inst. of
Technology• Parallel version from Sergey Napalenok, USEPA
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Domain for the Case Study
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• Impact of reductions in NOx emissions from five states:
• DE, MD, NJ, NY, and PA• Base Case:
• OTC12 BaseB
Case Study
• Evaluate performance of HDMR and DDM as surrogate models• 10% overall• 25% overall• 75% overall except PA (zero
reduction)
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Base Case (08/01/2002; Hours 14-17)
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10% overall reduction; HDMR (08/01/2002; Hours 14-17)
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25% overall reduction; HDMR (08/01/2002; Hours 14-17)
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75% overall reduction [except PA]; HDMR (08/01/2002; Hours 14-17)
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10% overall reduction; DDM (08/01/2002; Hours 14-17)
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25% overall reduction; DDM (08/01/2002; Hours 14-17)
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75% overall reduction [except PA]; DDM (08/01/2002; Hours 14-17)
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Discussion
• Approximations appear to break at about 25% changes in emissions
• Can be used for screening purposes for small variations• Potential mix of “global” and “gradient-based” sensitivities
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