ACCESS NUMBER: 31021

STUDY TITLE: Gulfwide Emission Inventory for the Regional Haze and Ozone 

Modeling Effort 

REPORT TITLE: Gulfwide Emission Inventory for the Regional Haze and Ozone 

Modeling Effort 

CONTRACT NUMBER(S): 1435-01-00-CT-31021 

SPONSORING OCS REGION: Gulf of Mexico 

APPLICABLE PLANNING AREA(S): Central and Western Gulf of Mexico 

FISCAL YEAR(S) OF PROJECT FUNDING: 2000; 2001; 2002; 2003; 2004 

COMPLETION DATE OF REPORT: October 2004 

COST(S): FY 2000 $86,890; FY 2001: $149,440; FY 2002: $289,345; FY 2003: 

$88,520; FY 2004: $131,929; CUMULATIVE PROJECT COST: $746,124 

PROJECT MANAGER(S): D. Wilson 

AFFLIATION: Eastern Research Group, Inc. 

ADDRESS: 1600 Perimeter Park Drive, Morrisville, North Carolina 27560 

PRINCIPAL INVESTIGATORSS: D. Wilson, R. Billings, A. Blackard, B. Boyer, S. Finn, 

R. Oommen. 

KEY WORDS: Air pollutant emissions inventory, Gulf of Mexico, GOADS, criteria 

pollutants, greenhouse gases. 

BACKGROUND: Measurements of ozone concentrations in onshore areas of Texas 

and Louisiana periodically exceed the national standard for one-hour ozone in 

nonattainment areas, with some observations nearly three times the national standard. 

Shoreline and inland locations in Texas and Louisiana could potentially be influenced by 

emission sources in the Gulf of Mexico. The Minerals Management Service (MMS) is 

responsible for determining if air pollutant emissions from Outer Continental Shelf 

(OCS) oil and natural gas platforms and other sources in the Gulf of Mexico influence 

the ozone attainment and nonattainment status of onshore areas. Consequently, MMS 

initiated a research study to develop a base year 2000 inventory of criteria air pollutant 

emissions and greenhouse gas emissions from offshore oil and gas exploration, 

development, and production in the Gulf of Mexico. The inventory also includes nonOCS oil and gas production sources such as the Louisiana Offshore Oil Port (LOOP), 

military vessels, and commercial marine vessels. 
ACCESS NUMBER: 31021

OBJECTIVES: 1- Describe and quantify emission sources in the OCS that release 

criteria air pollutants (i.e., carbon monoxide, sulfur dioxide, nitrogen oxides, particulate 

matter, and volatile organic compounds) and greenhouse gases (i.e., carbon dioxide, 

methane, and nitrous oxide) over the course of one calendar year; 2- prepare a report 

that summarizes the emissions data, describes the methodology used to generate the 

emissions inventory; 3- prepare data files for platform and non-platform emissions 

sources that can be used in air quality modeling studies; and 4- update and improve the 

computer software used to collect activity data for oil and gas production platforms, and 

the Oracle program used to develop the emission estimates. 

DESCRIPTION: The Gulfwide Emission Inventory Study includes all oil and gas 

production platforms and non-platform sources in the Central and Western Gulf of 

Mexico. Pollutants covered in the inventory are the criteria pollutants as well as 

greenhouse gases. MMS attempted to collect activity data from every active offshore 

oil production platform in the Gulf. Operators were provided with the Gulfwide Offshore 

Activities Data System (GOADS) Visual Basic activity data collection software for 

compiling monthly data for calendar year 2000. Nearly 2,900 oil and gas production 

platforms submitted monthly equipment activity data files. Non-platform sources were 

also included in the inventory, such as pipelaying vessels, drilling vessels, and support 

helicopters and vessels. Rigorous quality assurance/quality control (QA/QC) activities 

were performed on the activity data collected from platform operators. The monthly 

activity data collected from the platform operators were then combined with emission 

factors and algorithms to develop the platform production equipment emission 

estimates. Base year 2000 activity data for non-platform sources were collected and 

combined with emission factors to develop emission estimates for non-platform sources 

in the Gulf. Inventory data files were compiled with the oil and gas production platform 

data, suitable for use in air quality modeling applications. In addition to monthly 

emission estimates by pollutant and individual piece of equipment, the files include the 

company, structure, and complex ID, lease number, block and area number, and 

latitude/longitude. For each piece of equipment, stack parameter information such as 

outlet height, exit velocity, and exit temperature is also presented. Non-platform 

emission estimates were allocated using Geographic Information System (GIS) software 

to lease blocks and areas. 

SIGNIFICANT CONCLUSIONS: Because this inventory includes volatile organic 

compound (VOC) and methane, the data gathering effort for oil and gas production 

platforms includes new emission sources such as losses from flashing, pneumatic 

pumps, and pressure/level controllers. For OCS oil and gas production platforms, 

activity data were submitted by 55% more platforms than in a previous 1995 emission 

inventory effort performed by MMS. For carbon monoxide (CO), emissions reported in 

this study increased four-fold, primarily because of natural gas engines. Emissions did 

not show an increase for all pollutants, however. For VOC, emissions in the current 

study are slightly lower than in the 1995 study. The two studies have a similar number 

of boiler, diesel and natural gas engine, and natural gas turbine units (irrespective of the 
ACCESS NUMBER: 31021

increased number of platforms included), but emission estimates for nitrogen oxides 

(NOx) and particulate matter (PM) are higher in the 1995 study. Estimates for both 

studies were developed based on U.S. Environmental Protection Agency (EPA) 

published emission factors, and the factors have changed for natural gas engines and 

natural gas turbines. For example, the average NOx emission factor for natural gas 

engines is 50% lower than the factor applied in the 1995 study. The contribution of 

natural gas engines to total NOx emissions accounts for a large portion of the decrease 

in emissions compared to the 1995 study. In addition, the particulate matter emission 

factor is 65% lower for natural gas engines. Emissions of sulfur dioxide (SO2)

decreased significantly in the Gulfwide Study, primarily due to the amine unit estimates. 

The Gulfwide Study non-platform inventory built upon the 1995 inventory such that 

many of the assumptions made in the earlier inventory were used in this study, 

especially with regard to typical vessel horsepower and operating load, seasonal 

variation, and hours of operation. However, the Gulfwide Study estimates were based 

on more recent emission factors, and activity data specific to 2000. In many cases, the 

difference between the 1995 study estimates and those in the Gulfwide Study are due 

to the use of different marine diesel emission factors. The 1995 study was based on 

older EPA emission factors, while the Gulfwide Study estimates were based on the 

marine diesel emission factors derived from regression analysis performed on recent 

marine diesel emissions testing data. These new emission factors were recently 

developed to support the EPA’s new marine diesel rule making. 

STUDY RESULTS: The inventory results indicate that OCS oil and gas production 

platform and non-platform sources emit the majority of criteria pollutants in the Gulf of 

Mexico. OCS platform and non-platform sources account for 89% of total CO 

emissions, 77% of NOx emissions, 72% of VOC emissions, 69% of PM emissions, and 

66% of SO2 emissions. Oil and gas production platforms account for the majority of the 

CO, VOC, and NOx emissions. Non-platform OCS oil and gas production sources such 

as support vessels and drilling vessels emit the majority of the estimated SO2 and PM 

emissions. Platform sources account for almost all of the greenhouse gas emissions. 

Commercial marine vessels and vessel lightering are the top-emitting non-OCS oil and 

gas production sources in the inventory. 

Recommendations for future inventory efforts for platform sources in the Gulf of Mexico 

focus on the data gathering tools used. There is high uncertainty associated with the 

losses from flashing, vent, and flare emission estimates. Much of the uncertainty is 

thought to be due to the interpretation of the data requested by the operators. Work is 

underway to improve the GOADS software for these equipment types. In addition, an 

overall improvement will be made to the software to simplify the data requested each 

month to only the equipment variables that change monthly. This will reduce data entry 

volume, processing time, and the likelihood of data entry errors. 
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For non-platform sources, implementation of a survey of marine vessels supporting 

offshore oil platforms can provide important data that would allow for the development 

of a more accurate estimate of emissions from support vessels. This support vessel 

survey could collect detailed information about vessel size, horsepower rating, and 

typical operating loads, as well as annual and seasonal activity. The new survey vessel 

inventory could be used to develop emission estimates in terms that can be readily 

applied to state-of-the-art GIS tools to spatially allocate emissions with greater 

accuracy. For drilling vessels, MMS collects very specific data on where specific drill 

ships operate and the length of time they spend at a given site. In the Gulfwide 

inventory, the average horsepower and load data were used to estimate emissions from 

these sources. Some vessels may be significantly larger or smaller than these average 

values; however, such that actual emissions may differ significantly from the estimated 

emissions. A drill ship database could contain information about vessel size, the 

number and horsepower of the primary propulsion engine and ancillary engines, and 

better estimates on typical operating loads. This database could be linked up with 

MMS’s drill ship-specific activity data and available emission factors to provide more 

accurate emission estimates. 

STUDY PRODUCT(S): Wilson, D.L., J.N. Fanjoy, and R.S. Billings. 2004. Gulfwide 

Emission Inventory Study for the Regional Haze and Ozone Modeling Effort: Final 

Report. U.S. Dept. of the Interior, Minerals Management Service, Gulf of Mexico OCS 

Region, New Orleans, LA. OCS Study MMS 2004-072. 273 pp. 

Wilson, D., A. Blackard, S. Finn, and B. Boyer. 2001. Air Quality: User’s Guide for the 

Gulfwide Offshore Activities Data System (GOADS), Final Report. U.S. Dept. of the 

Interior, Minerals Management Service, Gulf of Mexico OCS Region, New Orleans, LA. 

OCS Study MMS 2001-052. 90 pp.