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Adaptation and Application of the CMAQ Modeling System for Real-time Air Quality Forecasting During the Summer of 2004
R. Mathur, J. Pleim, T. Otte, K. Schere, J. Young, G. Pouliot, B. EderAtmospheric Sciences Modeling Division, ARL/NOAA, NERL/U.S. EPA
D. Kang, S. Yu, H.-M. LinScience and Technology Corporation
J. McQueenNational Centers for Environmental Prediction
P. Lee, M. TsidulkoScience Applications International Corporation
D. WongLockheed Martin Information Technology
Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy
Eta-CMAQ AQF System
Eta-12Eta-12
CMAQCMAQ
Eta PostEta Post
PRDGENPRDGEN
PREMAQPREMAQ
AQF PostAQF Post
Verification ToolsVerification Tools
Vertical interpolation from eta to sigma
Horizontal interpolation to Lambert grid
CMAQ-ready meteorology and emissions
Gridded ozone files for users
Chemistry model
Meteorology model
Performance feedback for users and developers
CMAQ Configuration
• Structural– Netcdf replaced with binary IOAPI
• Advection– Horizontal: Piecewise Parabolic Method– Vertical: Upstream with rediagnosed vertical velocity
to satisfy mass conservation
• Turbulent Mixing– K-theory; PBL height from Eta
– New scheme for specification of minimum Kz
CMAQ Configuration (contd.)
• Gas phase chemistry– CB4 mechanism with EBI solver
• Cloud Processes– Mixing and aqueous chemistry: following the scheme in RADM
• Deposition– Dry : M3dry modified to use Eta land surface parameters– Wet
• Aerosols– 2004 release version
166
142
268 grid cells
259gridcells
Northeast“1x” Domain
East “3x” Domain
CMAQ Modeling Domains
Ozone forecasts on 3x and 1x Experimental PM forecasts on 3x
Lateral Boundary Condition Specification
A key uncertainty in long term modeling over limited area domains– Determines “model background”
• Default profiles– “Clean” tropospheric background values– Used in 1x
• Seasonal Profiles– Derived from continental CMAQ simulations for 2001– Used in 3x
Lateral Boundary Conditions (contd.)
• Ozone profiles from NCEP’s Global Forecast System (GFS)– O3 is a 3-d prognostic variable
– Initialized with Solar Backscatter Ultra-Violet (SBUV-2) satellite observations
– Motivation• Simulating varying dynamical conditions
• Improve model representation of O3 in the free troposphere
– Effects associated with intrusions
– Study FT-BL exchange mechanisms
Specification of Minimum Kz
• Minimum value of Kz allowed to vary spatially depending on urban fraction (furban)
• Kz = 0.1 m2/s, furban = 0• Kz = 2.0 m2/s, furban = 1
– allows min. Kz in rural areas to fall off to lower values than urban regions during night-time; mimics urban heat island effects
– prevents precursor concentrations (e.g., CO, NOx) in urban areas from becoming too large at night
– lower Kz (and reduced mixing intensity) in non-urban areas results in increased night-time O3 titration
• Helps reduce night time over predictions of ozone “regionally”
Summer 2004: Atypical Ozone Season
July 21
Aug. 12Source: EPA AIRNOW
Model Performance Characteristics: Summer 2004
Bias
Effects of GFS Ozone and Cloud Mixing
O3
Vertical profile Cloud top
GFS Sensitivity Simulations
• Limit GFS use to above a specified altitude– 6 km– 10 km
• Motivation: to limit the use of GFS derived O3 profiles to the upper levels of the model, where there is greatest confidence in GFS predictions and to avoid abnormally high O3 within the boundary layer (noticed in early parts of May)
• Default BC (without GFS)
Target Day Stats: May 18, 2004
Impact of GFS 6km and min. Kz change1x domain
Solid lines-with changes Dashed lines-without changes
Implemented in 1x domain on 7/20/04
Hourly 1 Hr. Max 8 Hr. Max
Comparison of 3x and 1x PerformanceAt sites within the 1x domain
Comparison of 3x and 1x Lateral Boundary Conditions
Solid lines (3x); filled circles and dash line (1x)
CMAQ 2001 Performanceat 3x Western Boundary
Solid lines: seasonal BCsDash/dots: Default profile
“Switch-Off” top-down cloud mixing
Tropopause limiton cloud top
Diagnostic Tests: Cloud Mixing
Diagnostic Tests: Cloud Mixing Target Day Stats: May 18, 2004
FSIDE: switch-off top-down mixingTROPLIM: tropopause limit on cloud top
Diagnostic Tests: Cloud effects on Photolysis
O3 (ppb)
Cloud Fraction: Current (average)
Cloud Fraction: Modified (max)
Scale by Radiation reaching the surface 1-(J/Jclear)
Photolysis Attenuation August 12, 2004
Effects of Cloud Process ModificationsMaximum Reductions in O3
August 12, 2004
Below cloud attenuation based onradiation
Below cloud attenuation based onRadiation + switch-off top-down mixing+New CFRAC
Effects of Cloud Process ModificationsAugust 12, 2004
rad_atten: cloud mixing + photolysis attenuation modifications
Comparison with Previous Day PersistenceMax. 1 Hr. Ozone
Persistence Eta-CMAQ
Correlation coefficient plots from S. McKeen
PM2.5 Forecast Comparisons with AIRNOW : Preliminary Daily Average
August 15 August 16 August 17
Summary
• Lateral boundary conditions play a dominant role in regulating modeled O3 background levels– Critical when ozone levels are relatively low as in the past two
summers– Higher O3 BC led to a systematic higher bias in the 3x simulation
• Careful consideration needs to be given in deriving LBCs from larger scale models– Are conditions representative?
• Bias propagation
– Consistent coupling
• Over-predictions at low O3 range related to representation of cloud processes– Top-down mixing– Photolysis attenuation
Looking ahead ….
• Methods to improve coupling between models– Boundary conditions
• GFS, Eta, CMAQ• Layer structure and model top to improve representation of
tropopause dynamics• Comparison of model (GFS, CMAQ) and observed free-
tropospheric O3 values
– Radiation• Photolysis attenuation
– Boundary layer mixing• Revisit Eta-Kh
– Transition to WRF• Advection on E-grid
– Minimize interpolations
Looking ahead ….
• Continue testing alternate formulations over a wider range of conditions – Mixing
– Below cloud washout (low observed O3 during precipitation events)
• Assessment of experimental PM forecasts results– Surface data: AIRNOW, IMPROVE, CASTNET– Satellites
• AOD