Modeling Protocol for the OTC CALGRID 

Screening-Level Modeling Platform for the 

Evaluation of Ozone 

May 23, 2007 

New Hampshire Department of Environmental Services 

Air Resources Division 

29 Hazen Drive 

Concord, NH 03302

 
1.0 Introduction

The Ozone Transport Commission (OTC) has sponsored the development of a 

photochemical modeling system to assist states in the preparation of their State 

Implementation Plans (SIPs) for attaining the eight-hour National Ambient Air Quality 

Standard (NAAQS) for ozone. The Community Multiscale Air Quality Model (CMAQ) 

is the basis of the OTC SIP-quality modeling platform that is being used in states’ eighthour ozone attainment SIPs. 

Running the CMAQ modeling platform is very resource intensive and usually requires 

the use of a Unix-based operating system. Therefore, the CMAQ modeling that is being 

done in support of the eight-hour ozone SIPs is limited to a handful of modeling centers 

that have the necessary expertise and computer resources. Similarly, because of the 

substantial effort, time, and storage space required to run the SIP-quality CMAQ 

platform, it is impractical to assess a large number of run scenarios. 

Consequently, OTC sponsored the development of an additional grid-based 

photochemical modeling platform that states could use as a screening tool for running 

additional emissions control strategies or performing sensitivity runs. The requirements 

for this additional modeling platform were that it be flexible, portable, and easily 

accessible to agencies that wish to use it. In this manner, a larger number of run 

scenarios could be modeled, allowing states to screen a wider variety of potential control 

strategies. 

The California Grid Model (CALGRID) was selected as the basis of this screening 

platform. CALGRID is a grid-based photochemical modeling platform that is designed 

to be run in a Windows environment. CALGRID has recently undergone a series of 

improvements and enhancements, with the most recent version being designated 

CALGRID Version 2.45. CALGRID Version 2.45 is being used as the screening 

platform for the OTC eight-hour ozone attainment SIPs. This document outlines the 

manner in which CALGRID will be used in these efforts. 

2.0 Platform Description and Model Inputs

To make the CALGRID modeling platform the best possible tool to supplement the SIPquality CMAQ platform, it was decided that CALGRID would be run on the same 

modeling domain using a common set of model inputs. All boundary conditions, 

meteorology, and emissions inputs were the same as those used for the SIP-quality 

CMAQ platform. Processing programs were written to convert these inputs into a format 

useable by the CALGRID model. The modeling domain and model inputs are described 

in the sections below. 

2.1 Modeling Domain

The OTC CMAQ/CALGRID modeling domain was set up on a Lambert Conic 

Conformal projection and covers the eastern United States and parts of Canada. The 

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southwest corner of the domain was set at 264 km, -888 km and the northeast corner was 

set to 2328 km, 1176 km. A 12-km grid cell resolution was used with 172 grid cells in 

the east-west direction and 172 grid cells in the north-south direction. For the vertical 

grid definition, 22 layers were used in the CMAQ simulations. For CALGRID, the 

processing programs that were used to reformat the boundary conditions, meteorology, 

and emissions mapped the 22 layers used for CMAQ to a total of nine vertical layers for 

the CALGRID modeling. The OTC CMAQ/CALGRID modeling domain is shown in 

Figure 1. 

Figure 1: Map of the OTC CMAQ/CALGRID Modeling Domain

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2.2 Boundary Conditions 

For the OTC CMAQ modeling, boundary conditions were derived from GEOS-Chem 

(Goddard Earth Observing System) global atmospheric simulations by running CMAQ 

on the 36-km continental grid. For the CALGRID platform, initial conditions, side 

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boundary conditions, and top layer concentrations were derived from the CMAQ 

boundary conditions files by means of a processing program. This program mapped the 

22 vertical layers used in the CMAQ simulations to the nine layers used with CALGRID. 

It produced the necessary side boundary file and top layer concentration file for each 

modeled episode day. It also produced an initial conditions file for each episode day 

processed; these files could be retained so that the user could begin a CALGRID 

simulation on any desired episode day. 

2.3 Meteorology

The meteorological modeling that was done in support of the OTC CMAQ SIP-quality 

modeling platform was performed by the University of Maryland (UMD) in conjunction 

with staff at the New York State Department of Environmental Conservation (NYSDEC). 

UMD used the Penn State/National Center for Atmospheric Research 5th Generation 

Mesoscale Model (MM5) Version 3.6 to generate year 2002 meteorological inputs. The 

details of this work are described in NYSDEC’s Technical Support Document TSD-1a, 

Meteorological Modeling Using Penn State/NCAR 5th Generation Mesoscale Model 

(MM5), February 1, 2006. For the CALGRID modeling platform, a processing program 

was used to interpolate the MM5 outputs to the CALGRID modeling grid and map them 

to CALGRID’s vertical layer structure. QA/QC plots were generated during the 

processing to ensure the accuracy of the interpolated data. Figures 2 through 4 show 

example QA/QC plots from the re-formatting of the meteorological data. 

Figure 2: QA/QC Plot of Humidity Data

August 6, 2002 Hour 12

Humidity Layer 1

CALGRID 2.45 Modeling Domain

Humidity (ppm)

NHDES

7/18/06

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LCC Easting (km)

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Figure 3: QA/QC Plot of Temperature Data

August 6, 2002 Hour 18

Temperature Layer 1

CALGRID 2.45 Modeling Domain

Temp (K)

NHDES

7/23/06

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Figure 4: QA/QC Plot of Rainfall Data

August 12, 2002 Hour 17

Rain

CALGRID 2.45 Modeling Domain

Rain (inches)

NHDES

7/17/06

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LCC Easting (km)

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2.4 Emissions 

The Regional Planning Organizations (RPOs) and their contractors were responsible for 

preparing modeling emissions inventories for use in the OTC CMAQ SIP-quality 

modeling. The RPOs prepared a set of accurate, up-to-date, and quality assured 

emissions inventories for the 2002 Base Case and three future years, 2009, 2012, and 

2018. For the future years, emissions inventories were prepared for two emissions 

control scenarios: one reflecting those emissions controls that are in place or likely to be 

in place by 2009, and another that reflects additional control strategies that may be 

needed to demonstrate attainment with the eight-hour ozone standard. The first scenario 

is referred to as “On The Books/On The Way” (OTB/OTW), and the second is referred to 

as “Beyond On The Way” (BOTW). These inventories were broken down into the 

following general emissions source categories: biogenic, point, area, non-road mobile, 

and on-road mobile. 

Using these inventories, NYSDEC and the other modeling centers, the Virginia 

Department of Environmental Quality (VADEQ) and Northeast States for Coordinated 

Air Use Management (NESCAUM), generated the necessary emissions inputs for CMAQ 

using the Sparse Matrix Operator Kernel Emissions (SMOKE) model. For the 

CALGRID modeling effort, the pre-merged SMOKE emissions files were obtained from 

the modeling centers and re-formatted for input into EMSPROC, the emissions preprocessor for the CALGRID modeling system. The pre-merged SMOKE files that were 

obtained from the modeling centers were broken down into the biogenic, point, area, nonroad, and on-road categories mentioned earlier. These files by component were then 

converted for use with EMSPROC, thus giving users of the CALGRID modeling system 

the flexibility to analyze a wide variety of emissions control strategies. QA/QC plots 

were generated during the re-formatting of the emissions data to ensure that an accurate 

modeling inventory was generated for the CALGRID platform. Example emissions 

QA/QC plots are shown in Figures 5 through 8. 

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Figure 5: QA/QC Plot of Surface Source CO Emissions

Figure 6: QA/QC Plot of Surface Source VOC Emissions

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Figure 7: QA/QC Plot of Point Source NOx Emissions

Figure 8: QA/QC Plot of Point Source SO2 Emissions

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3.0 CALGRID Model Outputs

A variety of post-processing programs have been developed to assist users of the 

CALGRID modeling platform in visualizing and tabulating model results. These postprocessors are designed to take the hourly concentration output generated by the 

CALGRID model and produce statistical results for desired averaging periods and 

geographic areas. CALGRID can also generate output suitable for plotting with standard 

graphical packages such as the Center for Ocean-Land-Atmosphere Studies’ Grid 

Analysis and Display System (GrADS) or Golden Software’s SURFER. 

As with the CMAQ SIP-quality modeling platform, it was decided that the CALGRID 

screening results should be used in a relative manner. Ratios of model-predicted base 

case and future scenario concentrations would be applied to current monitored ozone 

design values to generate estimated future design values (DVFs) for the future-year 

scenario of interest. It is these DVFs that are used in the determination of attainment. 

4.0 Episode Selection

For the CMAQ SIP-quality modeling analysis, the five-month ozone season of 2002 was 

selected for modeling because it met EPA’s episode selection criteria of containing 

episode days that are meteorologically representative of typical high ozone exceedance 

days and that are severe enough that any control strategy that is predicted to reach 

attainment on those days would reach attainment on other less severe days. 

Similarly, the CALGRID screening platform was run for the summer period from May 15 

to September 15, 2002 for the 2002 Base Case and 2009 OTB/OTW and BOTW 

scenarios. However, running the full summer episode, even with the CALGRID 

screening platform, is very time-consuming and resource intensive. In order to increase 

production and maximize the number of scenarios that can be evaluated with the 

CALGRID screening platform, it was decided that shorter modeling episodes would be 

selected that adequately reproduced the results obtained by running the full summer 

episode. An extensive analysis was undertaken to run a number of shorter summer 

episodes and compare the resulting predicted DVFs with those obtained for the full 

summer episode. The 2002 Base Case and 2009 OTB/OTW scenarios were used in this 

evaluation. It was found that the combined DVFs calculated from the July 6 to July 23, 

2002 and July 30 to August 16, 2002 modeling episodes best represented those from the 

full summer episode (note that July 6th and July 30th are considered to be model warm-up 

days). 

5.0 CALGRID Model Performance Evaluation

A qualitative and quantitative assessment was made of the CALGRID screening 

platform’s ability to reproduce observed ozone concentrations. To assess its 

performance, the CALGRID screening platform was run for the 2002 Base Case for the 

July 30 to August 16, 2002 modeling episode. Predicted maximum eight-hour ozone 

concentrations at monitor locations were compared against observations for 2002. Figure 

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9 shows the relative bias between maximum eight-hour ozone observations and predicted 

CALGRID eight-hour ozone concentrations for the 2002 Base Case for the episode from 

July 30 through August 12. Figures 10 through 13 show plots of predicted 2002 Base 

Case ozone concentrations against 2002 observations for selected episode days. 

Although the CALGRID model has a tendency to over-predict, especially in the urban 

core areas of northern Virginia, Maryland, southeastern Pennsylvania, New York City 

and Boston, it does a reasonable job of reproducing the pattern of the 2002 maximum 

ozone observations. 

Figure 9: Relative Bias Between Maximum 8-hour Ozone Concentrations Predicted 

with CALGRID and Observations

Relative Bias (CALGRID minus Observed)

 -20 to -15

 -15 to -10

 -10 to -5

 -5 to -2

 -2 to 2

 2 to 5

 5 to 10

 10 to 15

 15 to 20

 20 to 50

Based on Model Data for 

July 30 - August 12, 2002

2002 Base Case Emissions

versus Observed Data

Green Circles are where

CALGRID Underpredicts

Red Triangles are where

CALGRID Overpredicts

NHDES 11/21/06

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Figure 10: Comparison of Maximum 8-hour Ozone Concentrations for August 11, 

2002

 Maximum 8-Hour Ozone Concentrations

CALGRID - 2002 Base Case

OTC Modeling Domain - August 11, 2002

Ozone

Concentrations

(PPB)

NHDES

11/21/06

 0 to 40

 40 to 50

 50 to 60

 60 to 70

 70 to 80

 80 to 90

 90 to 100

 100 to 150

Figure 11: Comparison of Maximum 8-hour Ozone Concentrations for August 12, 

2002

Maximum 8-Hour Ozone Concentrations

CALGRID - 2002 Base Case

OTC Modeling Domain - August 12, 2002

Ozone

Concentrations

(PPB)

NHDES

11/21/06

 0 to 40

 40 to 50

 50 to 60

 60 to 70

 70 to 80

 80 to 90

 90 to 100

 100 to 150

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Figure 12: Comparison of Maximum 8-hour Ozone Concentrations for August 13, 

2002

Maximum 8-Hour Ozone Concentrations

CALGRID - 2002 Base Case

OTC Modeling Domain - August 13, 2002

Ozone

Concentrations

(PPB)

NHDES

11/27/06

 0 to 40

 40 to 50

 50 to 60

 60 to 70

 70 to 80

 80 to 90

 90 to 100

 100 to 150

Figure 13: Comparison of Maximum 8-hour Ozone Concentrations for August 14, 

2002

Maximum 8-Hour Ozone Concentrations

CALGRID - 2002 Base Case

OTC Modeling Domain - August 14, 2002

Ozone

Concentrations

(PPB)

NHDES

11/27/06

 0 to 40

 40 to 50

 50 to 60

 60 to 70

 70 to 80

 80 to 90

 90 to 100

 100 to 150

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6.0 CALGRID Model Runs

The OTC CALGRID modeling platform will be run for the 2002 Base Case, 2009 

OTB/OTB, and 2009 BOTW. These simulations will be run for the full summer (May 15 

to September 15, 2002) episode as well as for the shorter summer modeling episodes 

described earlier. A variety of control scenarios and sensitivity runs will be performed 

for the shorter episodes as requested by the OTC Modeling Committee or individual state 

agencies. The results of these runs may be used to evaluate, at a screening level, any 

additional emissions reductions that may be required, thus relieving the technical burden 

on the CMAQ modeling centers. CALGRID screening results may also be used in 

individual states’ weight-of-evidence (WOE) analyses. If states request it, the CALGRID 

modeling platform will be delivered so that they may run additional modeling scenarios 

at their discretion. 

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