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Reducing Vertical TransportOver Complex Terrain in

Photochemical Grid Models

Chris Emery, Ed Tai, Ralph Morris, Greg YarwoodENVIRON International Corporation

Novato, California

8th Annual CMAS ConferenceChapel 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– Top layer spans 8-15 km– 3 to 5 layers above PBL– MM5 run for 34 layers

• WRAP CMAQ and FCAQTF CAMx runs use 2002 BCs– Ozone in layer 19

range 100-300 ppb

19-layer Structure

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1 31 61 91 121 151 181 211 241 271 301 331 361

J ulian Date

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Max (Layer 19)

Max (Layer 18)

Max (Layer 17)

Max (Layer 16)

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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:– 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 reduction19-layer 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 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

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GEOSCHEM Run 4, 19 layers Run 4, 34 layers

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Improved 2005 BCs

• Improved vertical weighting technique– 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 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 RunApril 2005, 4-km Grid

19-layer 22-layer 22-layer2002 BCs 2005 BCs 2005 BCs

Orig CAMx Orig CAMx Revised CAMx

- 1 1 5 0 - 1 1 0 0 - 1 0 5 0 - 1 0 0 0 - 9 5 0 - 9 0 0 - 8 5 0 - 8 0 0

- 5 0 0

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- 1 1 5 0 - 1 1 0 0 - 1 0 5 0 - 1 0 0 0 - 9 5 0 - 9 0 0 - 8 5 0 - 8 0 0

- 5 0 0

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- 1 1 5 0 - 1 1 0 0 - 1 0 5 0 - 1 0 0 0 - 9 5 0 - 9 0 0 - 8 5 0 - 8 0 0

- 5 0 0

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- 4 0 0

- 3 5 0

- 3 0 0

- 2 5 0

- 2 0 0

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m ax = 83 PPBm ax = 80 PPB m ax = 108 PPB

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Full Photochemical RunApril 2005, 12-km Grid

19-layer 22-layer 22-layer2002 BCs 2005 BCs 2005 BCs

Orig CAMx Orig CAMx Revised CAMx

0 4 0 5 0 6 0 7 0 7 5 8 0 8 5 9 0 9 5

m ax = 83 PPB m ax = 110 PPB m ax = 85 PPB-2200 -2000 -1800 -1600 -1400 -1200 -1000 -800 -600 -400

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Full Photochemical RunJuly 2005, 4-km Grid

19-layer 22-layer 22-layer2002 BCs 2005 BCs 2005 BCs

Orig CAMx Orig CAMx Revised CAMx

0 4 0 5 0 6 0 7 0 7 5 8 0 8 5 9 0 9 5

- 1 1 5 0 - 1 1 0 0 - 1 0 5 0 - 1 0 0 0 - 9 5 0 - 9 0 0 - 8 5 0 - 8 0 0

- 5 0 0

- 4 5 0

- 4 0 0

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- 2 0 0

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7 8

7 97 5

m ax = 80 PPB- 1 1 5 0 - 1 1 0 0 - 1 0 5 0 - 1 0 0 0 - 9 5 0 - 9 0 0 - 8 5 0 - 8 0 0

- 5 0 0

- 4 5 0

- 4 0 0

- 3 5 0

- 3 0 0

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7 8

7 97 5

m ax = 83 PPB- 1 1 5 0 - 1 1 0 0 - 1 0 5 0 - 1 0 0 0 - 9 5 0 - 9 0 0 - 8 5 0 - 8 0 0

- 5 0 0

- 4 5 0

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- 3 5 0

- 3 0 0

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- 2 0 0

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6 27 2

7 8

7 97 5

m ax = 85 PPB

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Full Photochemical RunJuly 2005, 12-km Grid

19-layer 22-layer 22-layer2002 BCs 2005 BCs 2005 BCs

Orig CAMx Orig CAMx Revised CAMx

0 4 0 5 0 6 0 7 0 7 5 8 0 8 5 9 0 9 5

m ax = 127 PPB-2200 -2000 -1800 -1600 -1400 -1200 -1000 -800 -600 -400

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m ax = 133 PPB

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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…