Reducing Vertical Transport
Over Complex Terrain in
Photochemical Grid Models
Chris Emery, Ed Tai, Ralph Morris, Greg Yarwood
ENVIRON International Corporation
Novato, California
8th Annual CMAS Conference
Chapel Hill, NC
October 20, 2009
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Introduction
• Regional photochemical models over predict springtime
ozone throughout the inter-mountain western U.S.
– CMAQ: 2002 WRAP
– CAMx: 2005 FCAQTF
– Typically ~20 ppb higher than remote measurements
• Results from stratospheric ozone levels in top model layer
– Enters CMAQ/CAMx via lateral boundary conditions (BCs)
 Derived from output of GEOS-CHEM global chemistry model
• Stratospheric ozone is too efficiently transported to
surface over complex/high terrain
– Rockies, Sierras, Cascades
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Introduction
2002 CMAQ Annual Max Daily 8-hour Ozone
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Introduction
• WRAP CMAQ and FCAQTF CAMx runs use 19 layers
16000
14000
12000
Height MSL (m)
– Top layer spans 8-15 km
– 3 to 5 layers above PBL
– MM5 run for 34 layers
19-layer Structure
10000
8000
6000
4000
2000
0
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• WRAP CMAQ and FCAQTF CAMx runs use 2002 BCs
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– Ozone in layer 19
range 100-300 ppb
Ozone [ppb]
Grid Cell
300
280
260
240
220
200
180
160
140
120
100
80
60
40
Max (Layer 19)
Max (Layer 18)
Max (Layer 17)
Max (Layer 16)
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31
61
91
121
151
181
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Julian Date
241
271
301
331
361
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Introduction
• Contributors to high ozone over the Rockies:
– High surface altitudes (2-3 km MSL)
 Surface is closer to stratosphere
– Deep PBL mixing and convection (through 4-6 km MSL)
 Couple surface to mid-troposphere
– Vigorous resolved vertical circulations (through 4-8 km MSL)
 Transport layer 19 ozone downward
• Solutions we’ve identified in this study:
– Coarse vertical grid structure (more aloft layers help)
– GEOS-CHEM BC interface (improved interpolation helps)
– Vertical advection technique (alternative approach helps)
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Approach
• Test bed: CAMx 2005 FCAQTF application
– Inert, ozone only, no sources/sinks
– Single 12-km regional grid covering western U.S.
– Track ozone IC/BC over April 2005
 Original IC/BC from 2002 GEOS-CHEM extraction (WRAP)
 New IC/BC from 2005 GEOS-CHEM extraction
• Test and evaluate several ideas:
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Modify input wind fields (smoothers, filters, etc.)
Improve treatment of CAMx top boundary condition
Test alternative vertical grid structures/resolution
Improve GEOS-CHEM interface technique
Modify CAMx vertical advection solver
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Modify Input Winds
• Original Rationale
– Vertical velocity derived from input horizontal winds
 CAMx and CMAQ “yamo” approaches are similar
– Filter strong divergences in input winds to calm vertical velocity
– Apply aggressively to upper layers only
– Test on 19-layer structure and compare to un-modified case
• Three approaches were investigated
– Smoother-desmoother approach of Yang and Chen (2008)
– Divergence minimization from CALMET (Scire et al., 2000)
– Mass filter of Rotman et al. (2004)
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Modify Input Winds
• Results
– Minor (~10 ppb) reductions in peak April ozone
– Troubling effects on vertical velocity profiles in upper layers
– CAMx surface ozone reductions not caused by improved vertical
advection
 Instead by artificial dilution of top layer ozone
 Caused by CAMx arbitrary top boundary condition (70 ppb)
• CAMx was revised to use “zero-gradient” top boundary
conditions for all subsequent tests
– Top BC assigned from top layer concentration (a la CMAQ)
– Removes artificial dilution of top layer
– BUT increases surface ozone
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More Model Layers
• Reprocess input meteorology, no smoothers/filters
– Zero-gradient top boundary condition
– Full 34 MM5 layer structure
 Runs ~2x slower than 19 layers, 10-15 ppb ozone reduction
– Intermediate 22 layers to improve resolution aloft
 Runs ~1.1x slower than 19 layers, ~10 ppb ozone reduction
19-layer
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22-layer
34-layer
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2005 Day-Specific BCs
• New 2005 GEOS-CHEM BCs recently became available
– Zero-gradient top boundary condition
– Much higher stratospheric ozone (occasionally ~1000 ppb)
 Higher surface ozone, different spatial patterns
– NOTE CHANGES TO COLOR SCALE!
19-layer
22-layer
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34-layer
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2005 Day-Specific BCs
• Issues found in GEOS-CHEM interface program
– High ozone bias in topmost layers for coarse vertical layer
structures
• We improved the vertical layer-weighting technique
– Figure below shows new ozone profiles
Vertical Profile of Ozone, 19 vs 34 layers
GEOSCHEM
Run 4, 19 layers
Run 4, 34 layers
Height above ground[m]
18000
16000
14000
12000
10000
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4000
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0
0
0.1
0.2
0.3
0.4
0.5
0.6
Conc
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Improved 2005 BCs
• Improved vertical weighting technique
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Zero-gradient top boundary condition
Lower stratospheric ozone, lower surface ozone
Ozone still higher than with 2002 BCs
NOTE CHANGES TO COLOR SCALE!
19-layer
22-layer
34-layer
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Revised Vertical Advection
• Revised vertical velocity calculation to remove downward
•
bias
Revised vertical solver to be consistent
– Zero-gradient top BC, improved lateral BC
– 40-70 ppb reduction in April maximum ozone
19-layer BASE
MODIFIED ADVECTION
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Revised Vertical Advection
• Comparison of 19, 22, and 34-layer configurations
– NOTE CHANGES TO COLOR SCALE!
19-layer
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22-layer
34-layer
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Full Photochemical Run
• Run CAMx on 36/12/4-km FCAQTF grids for April and
•
July 2005
Compare 3 runs:
– Original 19-layer, 2002 BCs*, original vertical advection
– New 22-layer, 2005 BCs, original vertical advection
– New 22-layer, 2005 BCs, revised vertical advection
• Look at monthly maximum 8-hour ozone fields on 12 and
4 km grids
*2002 BCs: stratospheric ozone levels removed in layer 19
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Full Photochemical Run
April 2005, 4-km Grid
19-layer
2002 BCs
Orig CAMx
22-layer
2005 BCs
Orig CAMx
22-layer
2005 BCs
Revised CAMx
-150
-150
-150
-200
-200
-200
68
-250
68
-250
60 59
63
-300
60 59
63
63
-300
64
-300
64
-350
-350
-350
-400
-400
-400
-450
-450
-450
-500
-500
-1150
-1100
-1050
-1000
-950
-900
-850
-800
-1100
-1050
-1000
-950
-900
-850
-800
max = 108 PPB
0
40
64
-500
-1150
max = 80 PPB
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68
-250
60 59
50
60
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80
85
-1150
-1100
-1050
-1000
-950
-900
-850
-800
max = 83 PPB
90
95
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Full Photochemical Run
April 2005, 12-km Grid
19-layer
2002 BCs
Orig CAMx
22-layer
2005 BCs
Orig CAMx
22-layer
2005 BCs
Revised CAMx
600
600
600
400
400
400
200
200
200
0
0
0
-200
-200
-200
-400
-400
-400
-600
-600
-600
-800
-800
-800
-2200
-2000
-1800
-1600
-1400
-1200
-1000
-800
-600
-400
-2200
-2000
-1800
max = 83 PPB
-1400
-1200
-1000
-800
-600
-400
-2200
40
50
60
70
75
80
-2000
-1800
-1600
-1400
-1200
-1000
-800
-600
-400
max = 85 PPB
max = 110 PPB
0
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-1600
85
90
95
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Full Photochemical Run
July 2005, 4-km Grid
19-layer
2002 BCs
Orig CAMx
22-layer
2005 BCs
Orig CAMx
22-layer
2005 BCs
Revised CAMx
-150
-150
-150
-200
-200
-200
78
-250
78
-250
72 62
75
-300
72 62
75
75
-300
79
-300
79
-350
-350
-350
-400
-400
-400
-450
-450
-450
-500
-500
-1150
-1100
-1050
-1000
-950
-900
-850
-800
-1100
-1050
-1000
-950
-900
-850
-800
max = 83 PPB
0
40
79
-500
-1150
max = 80 PPB
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78
-250
72 62
50
60
70
75
80
85
-1150
-1100
-1050
-1000
-950
-900
-850
-800
max = 85 PPB
90
95
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Full Photochemical Run
July 2005, 12-km Grid
19-layer
2002 BCs
Orig CAMx
22-layer
2005 BCs
Orig CAMx
22-layer
2005 BCs
Revised CAMx
600
600
600
400
400
400
200
200
200
0
0
0
-200
-200
-200
-400
-400
-400
-600
-600
-600
-800
-800
-800
-2200
-2000
-1800
-1600
-1400
-1200
-1000
-800
-600
-400
-2200
-2000
-1800
max = 127 PPB
-1400
-1200
-1000
-800
-600
-400
-2200
max = 129 PPB
0
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-1600
40
50
60
70
75
80
85
-2000
-1800
-1600
-1400
-1200
-1000
-800
-600
-400
max = 133 PPB
90
95
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On-Going Work
• Additional testing of modified CAMx for full
photochemical/PM applications
– Complete 2005 FCAQTF Application; evaluate ozone and PM
– O&G projects in Rocky Mountains
– Denver SIP modeling
• CMAQ exhibits similar problems
– EPA/ORD is working on a vertical advection modification
 See Young, Pleim, Mathur poster
– Interact with ORD and OAQPS
– Test improvements using a western U.S. CMAQ database
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Acknowledgement
• The authors acknowledge funding support from the
American Petroleum Institute (API)
• Questions…
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