Excerpt from: http://vista.cira.colostate.edu/TSS/Results/Emissions.aspx

Emissions Methods: Point Source Emissions

Stationary Point-Source Emissions

The stationary point source emission category includes those sources that are identified by point 

locations, typically because they are regulated and their locations are available in regulatory 

reports. In addition, elevated point sources will have their emissions allocated vertically through 

the model layers, as opposed to being emitted into only the first model layer. Point sources are 

often further subdivided into electric generating unit (EGU) sources and non-EGU sources, 

particularly in criteria inventories in which EGUs are a primary source of NOx and SO2. 

Examples of non-EGU point sources include chemical manufacturers and furniture refinishers. 

Point sources are included in both criteria and toxics inventories

Stationary point source emissions data for SMOKE consist of (1) Inventory Data Analyzer

(IDA)-formatted inventory files; (2) ancillary data for allocating the inventories in space, time, 

and to the Carbon Bond-IV chemistry mechanism used in CMAQ and CAMx; and 

(3) meteorology data for calculating plume rise from the elevated point sources. 

The development of the stationary point source emission inventories for WRAP regional 

modeling is described in this section. The discussion focuses on the development of the 2002 

Base inventory; emissions modeling for the 2002 Planning inventory and the 2018 base year 

inventory use the same processing approach. Variations to the modeling approach and specific 

revisions and enhancements incorporated into the final modeling versions of the inventories have 

been described previously (refer to the Emission Overview Documentation). Specific revisions 

are noted with respect to data sources and source categories for the Plan02 and Base18 emissions 

inventories. 

Data Sources

Non-Oil and Gas Sources

For the Base02 stationary point source inventories, actual 2002 data were used. Data sources 

include emissions developed by the RPOs for the U.S., version 2 of the year 2000 Canadian 

inventory, and the BRAVO 1999 Mexican inventory. Entirely new inventories for the six 

northern states of Mexico for stationary area, as well as stationary point, on-road mobile, and offroad mobile sources, were incorporated into the 2002 Planning inventories. These data were 

provided by ERG, Inc., who completed an updated 1999 emissions inventory for northern 

Mexico (Fields et al., 2006) and delivered these data in early 2006. 

The WRAP stationary point inventory consisted of annual county-level and tribal data provided 

by ERG, Inc. (2005). The CENRAP (E.H. Pechan et al., 2005a) and VISTAS (Stella, 2005) 
stationary point inventories consisted of an annual data set and monthly CEM data for selected 

EGUs. CENRAP and Alpine Geophysics provided these data directly to the RMC. The MANEVU and MRPO 2002 stationary point inventories were obtained from the MANE-VU and 

LADCO web sites, respectively. For the Base02 inventory, the RMC opted to use the summer 

season inventory to model the entire year for the MANE-VU states (E.H. Pechan et al., 2005b). 

The MRPO Base I stationary point inventory was used in the Base02 inventory. 

ERG, Inc. provided SMOKE-ready temporal profiles and cross-reference files for representing 

baseline EGU activities in the WRAP states. The RMC worked closely with ERG to refine the 

cross-references that associate the profiles with actual inventory sources. For additional 

information on the development and application of these profiles, refer to Fields et al. (2005). 

Alpine Geophysics, LLC, provided SMOKE-ready temporal profiles and cross-reference files for 

representing baseline EGU activities for non-WRAP EGUs

The WRAP RMC entered into a nondisclosure agreement with Environment Canada to obtain 

version 2 of the 2000 Canadian point-source inventory. This inventory represented a major 

improvement over the version of the data used in the preliminary 2002 modeling. For Mexico, 

the same BRAVO 1999 inventory used in the preliminary 2002 modeling (Tonnesen et al., 2005)

was used for the current Base02 inventory modeling. New inventory data for Mexico developed 

by ERG for the six northern Mexican states were used for the Plan02 inventories. 

The 2018 point area source emission inventories for WRAP, MANE-VU, and VISTAS were 

developed from county-level input data processed outside SMOKE. For the MRPO and 

CENRAP regions, 2018 projection factors (growth and control) were applied to the Plan02 

inventories. For all non-WRAP EGU sources, updated temporal profiles, as developed from the 

IPM for 2018 emissions were used

The Base02 inventory used updated meteorology data and improved the temporal allocation 

information relative to the preliminary 2002 modeling; the rest of the ancillary data for modeling 

stationary point sources remained the same (Tonnesen et al., 2005). The meteorology data that 

used to calculate plume rise for the elevated sources was version 2 of the 2002 MM5 data 

preprocessed for SMOKE and CMAQ with MCIP version 2.3 (Kemball-Cook et al., 2005). One 

major improvement to the temporal allocation data based on information provided by the 

VISTAS RPO was incorporated. For the VISTAS sources, we added EGU-based CEM profiles 

developed by Alpine Geophysics were included in the SMOKE modeling. These additions 

included new monthly profiles and month-specific weekly and diurnal profiles.

Oil and Gas Production Operations

The 2002 Base year emission inventory included a number of emissions sectors that WRAP had 

never modeled before, including oil and gas production operations. Emissions from oil and gas 

production operations have been sporadically reported by some states in their stationary area 

source inventories, but for the most part were missing from the modeling inventories. In the 

Base02 inventories, oil and gas production emissions were represented explicitly as both area and 

point sources in a handful of states across the WRAP region.

The oil and gas production emissions inventories for the WRAP states and for tribal lands in the 

WRAP region were provided as stationary area source and stationary point source IDA-formatted 
inventories. ERG, Inc. provided the point-source inventories with the rest of the stationary-point 

data (ERG, 2005a). ENVIRON provided the area source oil and gas inventories for non-CA 

WRAP states and for tribal lands in the WRAP region, along with spatial surrogates for 

allocating these data to the model grid (Russell and Pollack, 2005). For California, oil and gas 

inventories were extracted from the stationary area source data used in the preliminary 2002 

modeling. Oil and gas production emissions data for outside of the WRAP region, if they exist, 

are contained in the stationary area inventories received from the other RPOs. 

For 2018, ENVIRON and ERG provided projected inventory data for oil and gas operations for 

the WRAP states. Projection factors were used for all other RPOs. 

Emissions Modeling 

Non-Oil and Gas Sources

For Base02 emission inventory, SMOKE was configured to process the annual inventories for the

U.S., Canada, and Mexico and process hourly CEM data for the VISTAS and CENRAP states. 

SMOKE was configured to allocate these emissions up to model layer 15, which roughly 

corresponds to the maximum planetary boundary layer (PBL) heights across the entire domain 

throughout the year. As coarse particulate matter (PMc) is not an inventory pollutant but is 

required by the air quality models as input species, SMOKE was set to calculate PMc during the 

processing as (PM10 - PM2.5). Also, the SMOKE option WKDAY_NORMALIZE set to “No,” to

treat the annual inventories based on the assumption that they represent average-day data based 

on a seven-day week, rather than average weekday data. It was also assumed that all of the 

volatile organic compound (VOC) emissions in the inventories are reactive organic gas (ROG), 

and thus used SMOKE to convert the VOC to total organic gas (TOG) before converting the 

emissions into CB-IV speciation for the air quality models. To capture the differences in diurnal 

patterns that are contained in the CEM temporal profiles for the VISTAS and CENRAP states, 

SMOKE was configured to generate daily temporal matrices, as opposed to using a Mondayweekday-Saturday-Sunday (MWSS) temporal allocation approach. 

The quality assurance of the stationary point emissions followed the WRAP emissions modeling 

QA protocol (Adelman, 2004) and a suite of graphical summaries. Tabulated summaries of the 

input data and SMOKE script settings were used to document the data and configuration of 

SMOKE. The graphical QA summaries include, for all emissions output species, daily timeseries plots, annual time-series plots, and daily vertical profiles. These QA graphics are available 

at http://pah.cert.ucr.edu/aqm/308/QA_base02a36.plots/pt/plots/

As part of the QA process for new emissions scenarios, qualitative and quantitative comparisons 

are made between sequential cases to confirm that the results show the expected changes based 

on the incremental updates that are made between cases. The comparison of the Plan02 

emissions results with Base02 results was consistent with the revisions, as expected, except for 

the non-WRAP stationary point sources. Observed differences in these emissions were much 

larger than expected, considering that only the temporal profiles were updated for these sources. 
It was discovered that the IPM-derived temporal profiles used in Plan02 for the non-WRAP 

stationary point sources were intended for use only with IPM-projected 2018 inventories, not 

with the 2002 inventories. The use of these profiles caused the 2002 emissions for non-WRAP 

EGUs to increase dramatically in case Plan02. The IPM-derived temporal profiles were therefore 

replaced with baseline CEM temporal profiles calculated as 2000-2003 activity averages for the 

VISTAS states and with actual 2002 CEM-derived temporal profiles for the CENRAP, MANEVU, and MRPO states. 

Oil and Gas Emissions

The oil and gas production industry includes a large number of processes and equipment types 

that stretch from the wellhead to fuel distribution networks. Many of these processes emit 

significant quantities of nitrous oxides (NOx), volatile organic compounds (VOC) and other 

pollutants. Past emission inventories have estimated emissions from specific pieces of 

equipment, for limited geographic areas and for other segments of the industry. The largest oil 

and gas production facilities, gas plants and major compressor stations, have been previously 

inventoried as stationary sources. All states in the western region had previously compiled 

emission inventories for the year 2002 that included the major “point” emission sources in the oil 

and gas production industry. However, what was included in these emission inventories varied 

from state to state, depending on the permitting and/or reporting thresholds. 

Oil and gas production facilities that are geographically distributed and have lesser emissions 

than the point source threshold are considered area sources. Previously, there had not been a 

comprehensive emission inventory of oil and gas production operations in the western region that

covered both point and area sources. Nor had there been a methodology developed to produce an 

inventory of this scope. The current WRAP inventory of oil and gas emissions was developed by 

ENVIRON as part of a WRAP-funded study to develop and implement a uniform procedure for 

estimating area source emissions from oil and gas production operations across the western 

region (Russell and Pollack, 2005). The emphasis of this study was placed on estimating 

emissions of pollutants with the potential to impair visibility near Class I areas in the west, in 

particular NOx emissions. In developing the emission estimation methodology, considerable 

resources were devoted to incorporating the insights and guidance of a variety of stakeholders, as 

well as integrating the point source emissions estimates developed in previous inventory efforts. 

The 2002 oil and gas point source emissions have been adopted from the state inventories (ERG, 

2005a). The level of coverage in those inventories was evaluated and the point source emissions 

have been reconciled with emissions estimated using the newly developed area source inventory 

methodology.

Oil and gas point source emission inventories include location parameters. For the current oil 

and gas area source emissions, a new spatial allocation scheme was developed to facilitate the 

integration of these emissions sources into the WRAP regional haze modeling. New spatial 

surrogates were developed for each of the non-point oil and gas emission sources addressed by 

this inventory. These surrogates, which are based on the geographic locations of oil and gas 

production, will enable the appropriate spatial distribution of emissions from oil and gas 

production operations in the air quality modeling.
Finally, a procedure was formulated and implemented to project the emissions from oil and gas 

production operations to future year 2018. For the WRAP 2018 base case modeling, only those 

emission control strategies that have already been adopted are considered. Oil and gas 

production forecasts were drawn from several sources and combined with the emissions 

estimates produced for the 2002 inventory and information on future controls to arrive at the 

2018 inventory. Oil and gas point source projections are described in a separate report (ERG, 

2005b).

Inventoried Sources 

The WRAP Oil and Gas inventory was developed for a number of specific processes and 

equipment not previously inventoried. Emissions were estimated and modeled as both stationary 

point and distributed area sources. Major sources of NOx and VOC emission were the focus of 

the inventory. 

Major sources of NOx emissions include the following processes and equipment types:

 Compressor engines

 Drill rigs

 Wellheads

 CBM pump engines

Major sources of VOC emissions include the following processes and equipment types:

 Oil well tanks

 Oil well pneumatic devices

 Gas well pneumatic devices

 Gas well dehydrators

 Gas well flaring and venting

 Condensate tanks

For each of these equipment types and processes, new and/or revised estimation methodologies 

were developed and applied. A detailed discussion of these methodologies can be found in 

Russell and Pollack, 2005.

Spatial Allocation

For air quality modeling, the EPA default spatial allocation surrogates were not 

appropriate for the area source oil and gas production emissions. ENVIRON therefore developed 

a new set of spatial allocation surrogates to be used in SMOKE to allocate the county-level area 

source emissions to the appropriate oil and gas fields. Oil and gas operation emissions estimated 

as stationary point sources are allocated based on geographic coordinates. 

A total of four different surrogate categories were designed to allocate emissions from the twelve 

oil and gas emission source categories listed in Table 1. The oil, gas and water production 
surrogates were based on production data at known well locations, while the drill rig surrogate 

was based solely on the number and location of wells drilled.

Table 1. Emission sources and surrogate categories.

Source SCC Allocation Surrogate Surrogate Code

Drill rigs 2310000220 Drill Rigs 688

Oil well - heaters 2310010100 Oil Production 686

Oil well - tanks 2310010200 Oil Production 686

Oil well - pneumatic devices 2310010300 Oil Production 686

Compressor engines 2310020600 Gas Production 685

Gas well - heaters 2310021100 Gas Production 685

Gas well - pneumatic devices 2310021300 Gas Production 685

Gas well - dehydration 2310021400 Gas Production 685

Gas well - completion 2310021500 Gas Production 685

CBM pump engines 2310023000 Water production at CBM wells 687

Gas well - tanks, uncontrolled 2310030210 Gas Production 685

Gas well - tanks, controlled 2310030220 Gas Production 685

Once the well locations were known, creation of the surrogates took place in several steps, and 

relied on the use of ArcINFO GIS software.

1. All wells and drill rigs were labeled with the appropriate grid cell IJ values for the 36-km 

domain. 

2. For each individual well, the oil, gas and water production values were divided by the 

total oil, gas and water production values corresponding to the county in which the well 

was located. This division resulted in determination of the fraction of a county’s total 

production taking place at each well. In the case of drill rigs, the number of drills, rather 

than the production values, were used.

3. For each unique grid cell / county combination with wells, each well’s production 

fractions were summed to create the surrogate value. 

The surrogate values for each grid cell / county combination were reformatted to comply with the 

SMOKE emissions processor AGPRO file format and an accompanying SMOKE AGREF file 

was created. The purpose of the AGREF file, presented in Table 2, is to define the relationship 

between the 3-digit codes chosen to represent each of the four surrogate categories in the 

AGPRO file and the SCC codes for the twelve oil and gas emission categories to be allocated 

with these surrogates. This file also specifies which county/state/county (COSTCY) should use 

the given cross-reference. In this case, COSTCY is set to 000000 to indicate that all states and 

counties can use these cross-references.

Table 2. SMOKE gridding surrogate cross-reference (AGREF) file.

COSTCY SCC CODE

000000 2310000220 686

000000 2310010100 688

000000 2310010200 686
000000 2310010300 686

000000 2310020600 686

000000 2310021100 685

000000 2310021300 685

000000 2310021400 685

000000 2310021500 685

000000 2310023000 687

000000 2310030210 685

000000 2310030220 685

2018 Projection Methodology

The 2018 emission estimates from oil and gas production operations reflect the anticipated 2018 

emission levels with the future controls currently defined by state and federal regulation. The 

2018 oil and gas point source emissions inventory was prepared and reported separately by 

Eastern Research Group (ERG, 2005b). A detailed discussion of the development of the 2018 oil 

and gas inventory, including those sources modeled as area sources can be found in Russell and 

Pollack, 2005. 

There were two primary basic methods used to estimate 2018 county-level oil and gas emissions. 

The first and by far the dominant method was to develop growth factors that were then used to 

project from the 2002 oil and gas emissions. A second method was necessary to estimate 

emissions in the handful of counties that had no 2002 oil and gas emissions but are anticipated to 

see oil and gas development by 2018. The decision of which method was used to estimate 2018 

emissions was based on the existence of oil and gas emissions in 2002. Detailed discussions of 

each of the projection methods, data sources and methodologies for both cases are presented in 

Russell and Pollack, 2005. 

To QA the oil and gas production emissions, we used the WRAP emissions modeling QA 

protocol (Adelman, 2004) and a suite of graphical summaries. Comparisons of the spatial plots 

produced from SMOKE output with spatial plots provided by ENVIRON were reviewed to 

ensure these data were modeled correctly. Tabulated summaries of the input data and SMOKE 

script settings were used to document the data and configuration of SMOKE. The graphical QA 

summaries include, for all emissions output species, daily spatial plots, daily time-series plots, 

and annual time-series plots are available at 

http://pah.cert.ucr.edu/aqm/308/QA_base02a36.plots/wog/plots/.

Gridded Stationary Point Source Emission Inventory Summaries

Summaries of the gridded point source emissions for the Base02b, Plan02c and Base18b 

inventories by state and county, annual and seasonal periods, can be found on the TSS at: 

http://vista.cira.colostate.edu/tss/Results/Emissions.aspx. 
References

Adelman, Z. 2004: Quality Assurance Protocol – WRAP RMC Emissions Modeling with SMOKE, 

Prepared for the WRAP Modeling Forum by the WRAP Regional Modeling Center, Riverside, CA.

E.H. Pechan & Associates and Carolina Environmental Program, 2005: Final Report: Refinement of 

CENRAP’s 2002 Emissions Inventories, Prepared for the Central Regional Air Planning Association 

by E.H. Pechan & Associates, Inc., Durham, NC and the Carolina Environmental Program, Chapel 

Hill, NC, 

http://projects.pechan.com/CENRAP/Deliverables/2002%20Inventory%20Revisions/Report%20and

%20Supporting%20Files/Final/CENRAP_Base%20B_EI_Rpt_Final_Aug3105.doc

ERG. 2005a. "Quality Assurance of the 2002 WRAP Stationary Sources Emissions Inventory," 

Draft, December 5, 2005.

ERG. 2005b. "WRAP Point and Area Source Emissions Projections for the 2018 Base Case 

Inventory," Draft, December 21, 2005.

Kemball-Cook, S. et al., 2005: Draft Final Report, Annual 2002 MM5 Meteorological Modeling 

to Support Regional Haze Modeling of the Western United States, prepared for the WRAP by 

ENVIRON International Corporation, Novato, CA and the University of California at 

Riverside, Riverside, CA. 

http://pah.cert.ucr.edu/aqm/308/reports/mm5/DrftFnl_2002MM5_FinalWRAP_Eval.pdf

Russell, J. and A. Pollack. 2005. “Oil and Gas Emissions Inventories for the Western States” 

Final Report. Prepared for the Western Governors’ Association. December 27.

Stella, G., 2005: Base F Emissions Inventories by State and RPO, Prepared for the VISTAS Joint 

Work Group Meeting by Alpine Geophysics, LLC. http://www.vistassesarm.org/documents/VISTASJointWorkGroupMeeting09052005/2_StellaIPM2018Results22Sept2005.ppt

Tonnesen, G. et al., 2005: Final Report for the WRAP RMC for the Project Period March 1, 

2004 through February 28, 2005, Prepared for the Western Governors Association by 

ENVIRON International Corporation, Novato, CA. 

http://pah.cert.ucr.edu/aqm/308/ppt_files/emissions/nh3/Volume_I_FinalReport.3-07.pdf

U.S. EPA (U.S. Environmental Protection Agency), 2005d: North American Emission Inventories –

Canada, http://www.epa.gov/ttn/chief/net/canada.html.