ATTACHMENT-7 

Technical Report: 

CALGRID Ozone Simulations 

Technical Report: CALGRID Ozone Simulations 

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A-7-1 

Background 

Regional photochemical simulation of ozone concentrations in the South Coast Air 

Basin (Basin) in the development of the 2003 Air Quality Management Plan (AQMP) 

ozone attainment demonstration was conducted using three modeling platforms and 

two chemical packages. These included the Urban Airshed Model (UAM), the 

California Photochemical Grid Model (CALGRID) and the Comprehensive Air 

Quality Model with Extensions (CALGRID). The chemical modules included 

Carbon Bond IV (CB-IV) and the State Air Pollution Research Center module 

(SAPRC99). Prior to the release of the Draft 2003 AQMP, the CAMx modeling 

platform was removed from the stable of regional simulation models due to its baseyear performance in recreating peak observed ozone concentrations. Both UAM and 

CALGRID were retained for further evaluation for the Final AQMP and while UAM 

with CB-IV was selected as the modeling and chemical package for the Plan, 

CALGRID/SAPRC99 simulations continued to be conducted in support of the 

document and analysis. 

This technical report briefly outlines the characteristics of the CALGRID model, and 

its application for the August 3-7, 1997 ozone simulation. Also discussed are the 

model input preparation, modifications made to accommodate meteorological model 

output and performance for the base and future year simulations. The discussion also 

provides an analysis of future year projections of carrying capacity that adjusts model 

output to account for under prediction of base-year ozone.

CALGRID Air Quality Model 

The CALGRID model was developed under contract to the ARB (Yamartino, et. al., 

1989; Scire, et. al., 1989). The model featured full compatibility with the CALMET 

meteorological model and it was the first regional air quality simulation model to 

incorporate the SAPRC chemical mechanism. Recent upgrades to the CALGRID 

model include the addition of the CB IV chemical mechanism (Kumar et. al, 1992) 

and the upgrade of the numerical advection solver (Earth Tech, 1996a). Since its 

release, the CALGRID model has been the subject of a number of peer reviews (eg., 

Yamartino, et. al., 1992; Kumar, et. al., 1994) and comparisons with other air quality 

models (Kumar, et. al. 1994; Earth Tech, 1996b; Jiang et. al., 1998; Schulman and 

Moore, 1998). CALGRID has been widely used in the United States and overseas 

because it is not dependent on resource-intensive prognostic meteorological models 

for air quality model inputs (Phinis, et. al., 1993; Jaing, et. al., 1997a; Jaing, et. al., 

1997b; Silibello, et. al., 1998; Barna, et. al., 2000; Gimson, 2000; Vaughan and 

Lamb, 2002). 
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Adaptation of the CALGRID Air Quality Modeling System 

CALGRID simulations were conducted using the Southern California Ozone Study 

(SCOS97) modeling domain and meteorological data. Prior to implementing CALGRID, 

three potential limitations of the air quality model were identified and addressed. 

CALGRID model supported the CB4 and SAPRC90 chemical mechanisms; however, it did 

not contain the most recent SAPRC99f mechanism. While CALGRID model was fully 

compatible with the CALMET meteorological model it was not formulated to directly use 

output from the MM5 mesoscale prognostic model. Thirdly, because CALGRID was 

developed to link diagnostic meteorological model there was concern that the model did not 

contain numerical corrections for mass-divergent flows. 

By virtue of the accommodation of both the CB4 and the SAPRC chemical mechanisms, the 

chemical mechanism structure within the CALGRID code closely resembled the Flexible 

Chemical Mechanism of the UAM/FCM model. The UAM/FCM model (Kumar, et. al., 

1995) was written to allow the inclusion or modification of any chemical mechanism. 

Because of this resemblance, it was relatively straightforward to create an interface between 

the UAM/FCM model and CALGRID allowing modifications to the chemical mechanisms 

within CALGRID. When this interface was completed, two upgrades of the CALGRID 

model were made. The first upgrade replaced the SAPRC90 mechanism with SAPRC99f. 

(Note: the versions of the SAPRC99 chemical mechanism was not subject to peer review). 

The second upgrade expanded the CB4 mechanism to include explicit representation of 

MTBE and inert tracer species. The inert species provided for the simulation of nonreactive trajectories. 

A meteorological preprocessor was developed to marry the output of the MM5 prognostic 

model with the CALGRID/CALMET system. Meteorological products including the winds, 

temperature and diffusivity (vertical and horizontal) were converted from the MM5 output 

to the CALGRID input format. Vertical diffusivity was defined based on CALMET 

generated mixing heights. 

To address the issue of mass divergence, CALGRID was modified to require a nonreactive chemical species designated as ‘NONR’. Within CALGRID, the value of 

NONR is initialized with a concentration of 1 ppb and there are no emissions of 

NONR. After each one-half advection time step, all chemical species concentrations 

are normalized to NONR. In subsequent sensitivity tests of the modified CALGRID, 

the maximum mass divergence within the SCOS modeling domain was less than 

10%. 

Meteorological Model/Input Preparation 

The CALGRID ozone simulations were driven by the MM5 recreation of the August 

3-7, 1997 meteorological episode. Based on NOAA’s NCEP-model initialization, 

MM5 was simulated using three grid domains (see Figure A-7-1) and using 4-
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dimensional data assimilation. MM5 was based on a Lambert Conformal coordinate 

system. The four dimensional data assimilation benefited from the extensive surface 

monitoring and upper air radar wind and temperature-profiling network supporting 

the SCOS97 effort. The resolution of the model horizontal grid cell was 5-squared 

km in the inner domain. 

As in many past mesoscale meteorological modeling efforts in southern California, 

the complexity of the terrain and the uniqueness of the initial conditions give rise to 

unusual wind flow patterns in the higher elevations. Nocturnal slope flows area often 

greatly exaggerated with down-slope flows occurring in gusts. Modifications to the 

terrain specification have been made to overcome this aspect of the prognostic 

simulation. In this application, the terrain file was reduced by two thirds. 

Comparison of UAM and CALGRID Simulations 

Table A-7-1 provides a comparison of the key components of the CALGRID and 

UAM simulations. In general, emissions, base meteorological data, background and 

initial conditions are identical between the applications. Major differences occur in 

the chemistry, advection schemes and the vertical layer structures. CALGRID is 

designed for pollutant transport over large domains. UAM was designed for an air 

basin application. Meteorological data input to CALGRID from MM5 required the 

development of preprocessor software to convert the hydrostatic prognostic data and 

difusivity to fixed vertical layers. Based on the differences provided in the summary 

table it is easy to assume that the modeling applications will diverge greatly in their 

solution. However, model performance is remarkably similar.
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Figure A-7-1 

Nested MM5 Domains: 

The horizontal grid resolution of the outermost domain is 45 km, for the middle domain 

is 15 km, and for the fine scale domain is 5 km. 
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Table A-7-1 

Comparison of CALGRID and UAM Modeling Systems 

Parameter CALGRID UAM 

Modeling System 

Domain Size SCOS97 SCOS97 

Grid Size 5-Km 5-Km 

Vertical Layer Structure Fixed 16 Layers Variable 5-Layers 

Region Top 5000 meters 2000 meters 

Boundary/Top/Initial Conditions Modified EPA Clean* Modified EPA Clean* 

Modeling Coordinate System Lambert Conformal UTM 

Emissions 

Mobile Source EMFAC2002/Offroad/DTM4 EMFAC2002/Offroad/DTM4 

Area Source Joint ARB/District Joint ARB/District 

Point Source Local Districts Inventories Local Districts Inventories 

Emissions Allocation/Plume Rise 3-dimensional introduction Layer-1 with Briggs plume rise 

Chemistry 

Basic Module SAPRC99 CB-IV 

Chemical Solver Quasi Steady States analysis 

(QSSA) or Hybrid Solver 

quasi-steady state assumptions 

with Crank-Nicholson algorithm 

Photolysis Rates Radiation extinction as height 

above sea level. 

One-dimensional based on Zenith 

angle 

Meteorology 

Meteorological Data SCOS97 SCOS97 

Wind Model MM5-4DDA CALMET 

Advection Chapeau function based scheme 

with Forester filter 

Forward-upstream diffusivecorrected algorithm of 

Smolarkewicz 

Vertical Diffusivity/Diffusion Horizontal diffusion- based on 

stability class with adjusted wind 

speed, (Smagorinsky method) 

Vertical diffusivity –Combination 

of various method depending on 

stability and layer height 

Vertical diffusivity coefficient is 

calculated internally 

Dry Deposition Surface resistance model Roughness length, stability, wind 

speed, deposition factor 

Mixing Heights CALMET Holsworth 

Cloud Cover Yes None 

Mass Continuity Adjustment NONR O’Brien scheme 

* Modified EPA Clean include NO - 0.0 ppb, NO2 -2 ppb, and VOC - 20 ppbv. 

Base Year Model Performance 

Table A-7-2 summarizes the base-year performance statistics for the CALGRID 

simulation for August 5th and August 6th. Performance criteria are outlined in 

Appendix V of the 1994 AQMP. Figures A-7-2 and A-7-3 provide the tile plots of 

predicted maximum concentration. Figures A-7-4a through A-7-4q provide the 

diurnal plots (dplots) of predicted and observed ozone concentrations. 
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The CALGRID simulation meets all of EPA’s three-performance criteria in zones 3, 

4 and 5 on August 5th and meets two criteria in zones 3 and 4 on the August 6th. The 

simulation under predicts the Basin peak concentration on both days with the ratios 

valuing 0.88 and 0.90 on the 5th and 6th respectively. Model performance for NO2 in 

Zone 4, the primary ozone impact zone met criteria in five of six categories. NO2 

performance for the ratio of the unpaired peak concentrations and systematic bias met 

EPA criteria in each zone on August 6th. In general performance for NO indicated 

over prediction in zones 3 and 5 and under prediction in Zone 4. Overall, CO was 

under predicted in each zone, regardless of the day. 

As depicted in Figure A-7-2, the August 5th CALGRID simulation predicts peak 

ozone concentrations in the Riverside area, near the location where the maximum 

concentration was observed. Impacts are predicted throughout the western portion of 

Riverside County and concentrations between 140 and 160 ppb occur along the 

foothill regions of eastern Los Angeles and western San Bernardino Counties. The 

primary impact zone shifts towards the northern portion of Los Angeles County and 

the desert portion od San Bernardino County on August 6th. This is consistent with 

the UAM simulations and reflects the development of the observed eddy circulation 

and southerly flow through the modeling domain. 

Figures A-7-4a through A-7-4q illustrate the capacity of the CALGRID simulation to 

recreate the temporal ozone distribution. The diurnal ozone plots indicate that ozone 

is slightly over predicted in the San Gabriel Valley and San Fernando Valley. In 

addition, the general tendency observed throughout the Basin is for over prediction of 

morning ozone concentrations. The morning tendency is clearly observed throughout 

Zone 4. This is in contrast to the tendency to lag late in the day observed by the 

UAM simulations. 

Table A-7-3 provides an observational comparison of the performance of UAM and 

CALGRID for the base-year simulation. Also listed in the table are selected 

advantages and disadvantages of the use of either model. 

 
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TABLE A-7-2 

Comparative Performance Statistics 

Statistic Zone 3 Zone 4 Zone 5

 5th 6th 5th 6th 5th 6th 

Ozone Threshold (pphm) 6.0 6.0 6.0 6.0 6.0 6.0 

Ratio of Predicted Basin Peak 

to Peak Observed 

0.88 0.90 0.88 0.90 0.88 0.90 

Ratio of Unpaired Station 

Peaks 

0.98 1.19 0.84 0.83 1.06 1.54 

Systematic Bias (%) 5 25 11 9 -5 -3 

Gross Error (%) 29 35 35 37 23 62 

 

NO2 Threshold (pphm) 1.0 1.0 1.0 1.0 1.0 1.0 

Ratio of Unpaired Station 

Peaks 

0.44 0.82 0.58 0.75 0.49 0.92 

Systematic Bias (%) -59 -26 -42 -43 -24 -22 

Gross Error (%) 64 49 47 65 41 59 

 

NO Threshold (pphm) 1.0 1.0 1.0 1.0 1.0 1.0 

Ratio of Unpaired Station 

Peaks 

1.10 2.00 0.41 0.40 1.29 1.17 

Systematic Bias (%) -20 129 -32 -55 72 20 

Gross Error (%) 90 208 72 87 142 123 

 

CO Threshold (pptm)* 2.0 2.0 2.0 2.0 2.0 2.0 

Ratio of Unpaired Station 

Peaks 

0.79 1.75 0.68 0.62 0.85 0.93 

Systematic Bias (%) -51 -17 -27 -39 -12 -18 

Gross Error (%) 61 60 49 52 54 60 

Bold indicates numbers meeting performance goals. 

* Note: No performance criteria for 1-hour average carbon monoxide and nitric oxide were available. 
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Figure A-7-2 

Predicted Maximum 1-Hour Average Ozone Concentrations for August 5, 1997 Episode

Figure A-7-3 

Predicted Maximum 1-Hour Average Ozone Concentrations for August 6, 1997 Episode 
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Figure A-7-4a 

Simulated Maximum 1-Hour Average Ozone (Solid Line) Vs. Observed (Squares): 

August 3-7, 1997 Ozone Meteorological Episode 
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Figure A-7-4b 

Simulated Maximum 1-Hour Average Ozone (Solid Line) Vs. Observed (Squares): 

August 3-7, 1997 Ozone Meteorological Episode 
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Figure A-7-4c 

Simulated Maximum 1-Hour Average Ozone (Solid Line) Vs. Observed (Squares): 

August 3-7, 1997 Ozone Meteorological Episode 
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Figure A-7-4d 

Simulated Maximum 1-Hour Average Ozone (Solid Line) Vs. Observed (Squares): 

August 3-7, 1997 Ozone Meteorological Episode 
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Figure A-7-4e 

Simulated Maximum 1-Hour Average Ozone (Solid Line) Vs. Observed (Squares): 

August 3-7, 1997 Ozone Meteorological Episode 
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Figure A-7-4f 

Simulated Maximum 1-Hour Average Ozone (Solid Line) Vs. Observed (Squares): 

August 3-7, 1997 Ozone Meteorological Episode 
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Figure A-7-4g 

Simulated Maximum 1-Hour Average Ozone (Solid Line) Vs. Observed (Squares): 

August 3-7, 1997 Ozone Meteorological Episode 
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Figure A-7-4h 

Simulated Maximum 1-Hour Average Ozone (Solid Line) Vs. Observed (Squares): 

August 3-7, 1997 Ozone Meteorological Episode 
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Figure A-7-4i 

Simulated Maximum 1-Hour Average Ozone (Solid Line) Vs. Observed (Squares): 

August 3-7, 1997 Ozone Meteorological Episode 
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Figure A-7-4j 

Simulated Maximum 1-Hour Average Ozone (Solid Line) Vs. Observed (Squares): 

August 3-7, 1997 Ozone Meteorological Episode 
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Figure A-74k 

Simulated Maximum 1-Hour Average Ozone (Solid Line) Vs. Observed (Squares): 

August 3-7, 1997 Ozone Meteorological Episode 
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Figure A-7-4l 

Simulated Maximum 1-Hour Average Ozone (Solid Line) Vs. Observed (Squares): 

August 3-7, 1997 Ozone Meteorological Episode 
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Figure A-7-4m 

Simulated Maximum 1-Hour Average Ozone (Solid Line) Vs. Observed (Squares): 

August 3-7, 1997 Ozone Meteorological Episode 
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Figure A-7-4n 

Simulated Maximum 1-Hour Average Ozone (Solid Line) Vs. Observed (Squares): 

August 3-7, 1997 Ozone Meteorological Episode 
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Figure A-7-4o 

Simulated Maximum 1-Hour Average Ozone (Solid Line) Vs. Observed (Squares): 

August 3-7, 1997 Ozone Meteorological Episode 
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Figure A-7-4p 

Simulated Maximum 1-Hour Average Ozone (Solid Line) Vs. Observed (Squares): 

August 3-7, 1997 Ozone Meteorological Episode 
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Figure A-7-4q 

Simulated Maximum 1-Hour Average Ozone (Solid Line) Vs. Observed (Squares): 

August 3-7, 1997 Ozone Meteorological Episode 
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Table A-7-3 

General Observations 

Model Base Year Simulation 

Observations 

Model Advantages Model Disadvantages 

UAM (a) Peak concentration is south 

of observed 

(b) San Gabriel Valley 

generally under- predicted 

(c) NOx and CO reasonably 

well predicted in Zone 5 

source area 

(d) Peak concentration 

consistent with observations 

(a) Urban Application 

(b) Extensive Experience 

(c) Ease of use 

(a) Older advection 

schemes 

(b)Variable grid cell height 

based on mixing height 

(c) Mass continuity issues 

(d) Limited number of 

vertical layers 

CALGRID (a) Timing of peak and location 

well simulated 

(a) Broader area of ozone 

impact with morning peaks 

(b) Slight over-prediction of 

NOx in Zone 5 source areas 

(d) Peak concentration 88 

percent of observations 

(a) Urban/Regional Application 

(b) Coupled with CALMET 

Meteorological model 

(c) Fixed layers 

(d) advection designed for 

longer range transport 

(a) Minimal Experience in 

Modeling Community 

(b) Diagnostic 

meteorological model 

mass continuity issues 

(c) Requires MM5 

interface 

(d) More complex 

application 
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CALGRID 2002 Mid-Course Evaluation 

Table A-7-4 summarizes the 2002 CALGRID mid-course simulations compared to 

observed ozone air quality in 2002 while Figures A-7-5 and A-7-6 provide the 2002 

predicted spatial distribution of ozone. As discussed in Chapter 3, observed ozone on 

days having similar meteorological characteristics as August 5, 1997, ranged from 

140 to 170 ppb with an average of 150 ppb. The CALGRID simulation for August 

5th reached 141 ppb, within the 2002 observed range but far below the 169 ppb peak 

observed concentration. CALGRID predictions for August 6th fell below the range of 

observed ozone concentrations. 

TABLE A-7-4 

CALGRID 2002 Projected Maximum 1-Hour Ozone Concentrations (ppb) 

Episode Day CALGRID 

Predicted 

(ppb) 

4-Day 2002 

Historical Average 

Ozone (ppb) 

Range of 

Observations for 

Comparable days in 

2002 (ppb) 

August 5, 1997 141 150 140 - 169 

August 6, 1997 126 140 130 - 150 

2007 CALGRID Simulations 

One major component of the 2003 AQMP modeling attainment demonstration 

addresses the issue of transport of ozone and precursor pollutants into the Coachella 

Valley, Antelope Valley, South Central Coast and Mojave Desert. The attainment 

year for each of these areas is 2007. 

CALGRID predicted maximum ozone concentration maps for the year 2007 are 

presented in Figures A-7-7 and A-7-8 for the August 5th and August 6th 1997 

episodes. Controlled emissions are used for equivalent the 2007 projection. 

Emission reductions through 2007 are expected to take place through exiting 

established control measures and reductions in mobile source emissions as projected 

by EMFAC2002. Table A-7-5 lists the 2007 predicted ozone air quality for the 

Basin and its neighboring transport partners. 

While projected ozone concentrations in the Basin will exceed 124 ppb, by 2007 all 

areas of the Coachella Valley demonstrate attainment of the federal ozone standard. 
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A-7-28 

CALGRID projections of the 2007 one-hour maximum ozone concentrations for 

Ventura County (South Central Coast Air Basin), the Antelope Valley, and the San 

Bernardino County portion of the Mojave Desert indicate that all three areas will 

meet the federal standard. Also presented in Table A-7-5 Valley is an adjusted 

prediction for one-hour maximum ozone for the Antelope Valley and Mojave Desert. 

Both CALGRID and UAM over predicted ozone concentrations in the high desert for 

the August 6th base year simulation. For the UAM simulation, Hesperia and 

Victorville were over predicted by an average of 33 percent while Lancaster was over 

predicted by 43 percent. For the CALGRID simulation, Hesperia and Victorville 

were over predicted by 9 percent while Lancaster was over predicted by 71 percent. 

By adjusting the 2007 UAM simulation in the local area for the base-year over 

prediction the estimated Antelope Valley and Mojave Desert impacts are lowered to 

72 and 112 ppb, respectively. This correction is consistent with the projected is 

consistent with the direct CALGRID simulation for August 5th. 

TABLE A-7-4 

CALGRID 2007 Projected Maximum 1-Hour Ozone Concentrations (ppb) 

Episode Day Basin Coachella 

Valley 

Antelope 

Valley 

Mojave 

Desert 

VenturaSouth 

Central 

Coast 

August 5, 1997 135 121 107 105 95 

August 6, 1997 123 117 123 (72)* 122(112)* 112 

* Concentration for the high desert inside the brackets is the scaled value to adjust for systematic over 

prediction in the base year 
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Figure A-7-5 

Predicted 2002 Maximum 1-Hour Average Ozone for August 5, 1997 Episode 

Figure A-7-6 

Predicted 2002 Maximum 1-Hour Average Ozone for August 6, 1997 Episode 
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Figure A-7-7 

Predicted 2007 Maximum 1-Hour Average Ozone for August 5, 1997 Episode 

Figure A-7-8

Predicted 2007 Maximum 1-Hour Average Ozone for August 6, 1997 Episode 
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2010 CALGRID BASE-YEAR AND CONTROLLED SIMULATIONS 

Table A-7-6 presents the results of the CALGRID 2010 simulations for the base-year 

and control options 1 and 2. Figures A-7-9 through A-7-14 provide the tile plots of 

predicted maximum ozone fro the base-year and controlled scenarios. 

The 2010 base-year predicted peak concentrations predicted by CALGRID indicate 

that the both August 5th and August 6th will exceed the federal 1-hour standard if no 

further controls are implemented. The Basin will meet the federal standard with 

implementation of either control option-1 or control option-2. Again, it is important 

to note that the 1997 base-year simulations under predicted the maximum ozone 

concentrations and scaling of the modeled results will result in higher ozone impacts 

for both the controlled and baseline emissions scenarios. 

TABLE A-7-6 

CALGRID 2010 Projected Maximum 1-hour Ozone Concentrations (ppb) 

Episode Day 2010 Baseline 2010 Control 

Option-1 

2010 Control 

Option-1 

August 5, 1997 134 112 112 

August 6, 1997 127 109 108 
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Figure A-7-9

Predicted 2010 Baseline -Hour Average Ozone Concentrations for August 5, 1997 

Figure A-7-10

Predicted 2010 Baseline -Hour Average Ozone Concentrations for August 6 1997 
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Figure A-7-11 

Predicted 2010 Maximum 1-Hour Average Ozone for August 5, 1997 Episode Option-1 

Figure A-7-12 

Predicted 2010 Maximum 1-Hour Average Ozone for August 6, 1997 Episode Option-1 
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Figure A-7-13 

Predicted 2010 Maximum 1-Hour Average Ozone for August 5, 1997 Episode Option-2 

Figure A-7-14 

Predicted 2010 Maximum 1-Hour Average Ozone for August 6, 1997 Episode Option-2 
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A-7-35 

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