GHG Inventory Tracking and Emission Factors
A greenhouse gas inventory is an accounting of the amount of greenhouse gases emitted to or removed from the atmosphere over a specific period of time (e.g., one year). A greenhouse gas inventory also provides information on the activities that cause emissions and removals, as well as, background on the methods used to make the calculations. Policymakers use greenhouse gas inventories to track emission trends, develop strategies and policies and assess progress. Scientists use greenhouse gas inventories as inputs to atmospheric and economic models.
The U.S. Environmental Protection Agency (EPA), in cooperation with other U.S. government agencies, prepares the Inventory of U.S. Greenhouse Gas Emissions and Sinks. A wide range of agencies and individuals are involved in supplying data to, reviewing, or preparing portions of the Inventory—including federal and state government authorities, research and academic institutions, industry associations, and private consultants.
Within the EPA, the Office of Atmospheric Programs (OAP) is the lead office responsible for the emission calculations provided in the Inventory, as well as, the completion of the National Inventory Report and the Common Reporting Format tables. The Office of Transportation and Air Quality (OTAQ) is also involved in calculating emissions for the Inventory. While the U.S. Department of State officially submits the annual Inventory to the UNFCCC, EPA’s OAP serves as the focal point for technical questions and comments on the U.S. Inventory.
Several other government agencies contribute to the collection and analysis of the underlying activity data used in the Inventory calculations. Formal relationships exist between the EPA and other U.S. agencies that provide official data for use in the Inventory. The U.S. Department of Energy’s Energy Information Administration provides national fuel consumption data. The U.S. Department of Defense provides military fuel consumption and bunker fuels data. Informal relationships also exist with other U.S. agencies to provide activity data for use in the EPA’s emission calculations. Finally, the U.S. Department of State officially submits the Inventory to the UNFCCC each April.
Emission calculations for individual sources are the responsibility of individual source leads, who are most familiar with each source category and the unique characteristics of its emissions profile. The individual source leads determine the most appropriate methodology and collect the best data to use in the emission calculations. They base this upon their expertise in the source category, as well as coordinate with researchers and contractors familiar with the sources. A multi-stage process for collecting information from the individual source leads and producing the Inventory is undertaken annually to compile all information and data.
The EPA’s Emission Inventory Improvement Program (EIIP) was established in 1993 to promote the development and use of standard procedures for collecting, calculating, storing, reporting, and sharing air emissions data. The EIIP is designed to promote the development of emission inventories that have targeted quality objectives, are cost-effective, and contain reliable and accessible data for end users.
Volume 8 of the EIIP Technical Report establishes the standards and emission factors for calculating GHG emissions from various sources. Unfortunately, this volume is undergoing revision to:
- Increase consistency with the national inventory of GHG emissions and sinks
- Incorporate state-level data sources, methods and emission factors where applicable
- Update the text and examples for clarity
- Include references to a MS Excel® based tool designed to assist states in the estimation of emissions
The revised guide is in final draft form and is currently undergoing review.
One of the most useful tools available for estimating emissions from point, area, and mobile sources is the emission factor. An emissions factor is a representative value that attempts to relate the quantity of a pollutant released to the atmosphere with an activity associated with the release of that pollutant. These factors are usually expressed as the weight of pollutant divided by a unit weight, volume, distance, or duration of the activity emitting the pollutant (e.g., kilograms of particulate emitted per megagram of coal burned). Such factors facilitate estimation of emissions from various sources of air pollution. In most cases, these factors are simply averages of all available data of acceptable quality, and are generally assumed to be representative of long-term averages for all facilities in the source category (i.e., a population average). The general equation for emissions estimation is:
where:
E = emissions;
A = activity rate;
EF = emission factor, and
ER =overall emission reduction efficiency, %
Specific emissions measurement is generally the best and most accurate method to quantify emissions; however, source data are not always available. As an alternative, documents and databases containing emission factors and models can be used as tools to estimate air pollutant emissions for inventory purposes. The EPA’s Factor Information Retrieval System (FIRE) is a consolidation of emission factors for criteria pollutants that includes emission factors from EPA documents such as AP-42 (the compilation of air pollutant emission factors first developed back in the late 1960’s).
Each emission factor in FIRE also includes information about the pollutant (Chemical Abstract Service (CAS) numbers and chemical synonyms) and about the source (Standard Industrial Classification (SIC) codes and descriptions, and Source Classification Codes (SCCs) and descriptions). Each emission factor entry includes comments about its development, in terms of the calculation methods and/or source conditions, as well as references to where the data was obtained. The emission factor entry also includes a data quality rating.
The IPCC Emission Factor Database (EFDB) is an additional reference source for emission factor data. The EFDB is meant to be a recognized library, where users can find emission factors and other parameters with background documentation or technical references that can be used for estimating greenhouse gas emissions and removals. The responsibility of using this information appropriately will always remain with the users themselves.
EFDB at present contains only the IPCC default data (default data presented in the Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories and the IPCC Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories). It also contains the data from CORINAIR94, but please note that these data records may be renewed in due course in accordance with the latest version of CORINAIR data set (i.e., data in the Joint EMEP/CORINAIR Atmospheric Emission Inventory Guidebook, Third Edition. Copenhagen: European Environment Agency, 2001). It is highly recommended to consult the website at http://reports.eea.eu.int/EMEPCORINAIR4/en for details on CORINAIR data.
The Greenhouse Gas Protocol (GHG Protocol) Initiative is a multi-stakeholder partnership of businesses, non-governmental organizations (NGOs), governments, and others convened by the World Resources Institute (WRI) (a U.S.-based, environmental non-governmental organization (NGO)), and the World Business Council for Sustainable Development (WBCSD) (a Geneva-based coalition of 170 international companies)). First launched in 1998, the Initiative’s mission is to develop internationally-accepted GHG accounting and reporting standards for business as well as to promote their broad adoption.
The GHG Protocol Initiative comprises two separate but linked standards:
- Corporate Accounting and Reporting Standards: Provides a step-by-step guide for companies to use in quantifying and reporting their GHG emissions.
- Project Accounting Protocol and Guidelines: Provides a guide for quantifying reductions from GHG mitigation projects.
These standards contain tools and descriptions that provide step-by-step guidance and electronic worksheets to help users calculate GHG emissions from specific sources or industries. The tools are consistent with those proposed by the IPCC (and subsequently followed by the EPA) for compilation of emissions at the national level. They have been refined to be user-friendly for non-technical company staff and to increase the accuracy of emissions data at a company level. The GHG Protocol Initiative is more focused on the methods and procedures of GHG tracking and doesn’t focus as much on the software aspect. Therefore, it serves as an excellent model and guide for tracking GHG emissions.
