Emissions inventories

Summary: Emissions inventories are used by the Environmental Protection Agency and the United Nations to gather air quality data on gas and particulate matter.

Emissions inventories are born of a long history of air quality concerns and pollution legislation. In response to President Richard Nixon’s historic signing of the 1970 National Environmental Policy Act, the formation of the Environmental Protection Agency (EPA), and the United States’ first Earth Day celebration, the Clean Air Act was passed on the last day of 1970 and set new guidelines for individual states to guard against the buildup of pollutants such as hydrocarbons, sulfur dioxide, carbon monoxide, photochemical oxidants, nitrogen dioxide, and total suspended particulates. In tandem with additional U.S. and international regulations as well as antipollution advocates, the Clean Air Act has generated a great deal of interest in emissions studies, leading to research on and articulation of emissions inventories.

The Clean Air Act was amended again in the 1970s to increase constraints on suspended particulates but also to relax some standards for automobile pollution. In the 1980s, sulfur dioxide was added as a “secondary standard,” meaning additional regulation. Ambient air standards were also massaged over the next two decades such that legislators grew more and more concerned with issues of acid rain and what were eventually referred to as hazardous air pollutants (HAPs); as a result, the previous, short list grew to include ozone and lead. The 1990 Clean Air Act amendments set forth new guidelines for regulating air pollution, including a mandate for the EPA to review and to regulate hazardous air pollutants. By 1999, the EPA had generated a new program titled the National Air Toxics Assessment and commissioned what it referred to as a National Emissions Inventory. In 2024, the inventory gathered information on 181 out of 188 hazardous air pollutants.

Of course, generations of people had demonstrated various concerns over air pollution since the dawn of the industrial age, but it appears the U.S. EPA grew very active on the air pollution front in the same era that the United Nations investigated transboundary air quality and greenhouse gas (GHG) emissions. The 1979 Convention on Long-Range Transboundary Air Pollution grew out of the United Nations’ Economic Commission for Europe, charged with cleaning up pollution on the Continent. The United Nations’ 2006 Intergovernmental Panel on Climate Change (IPCC) was mandated, through a joint proposal on behalf of the World Meteorological Organization and the United Nations Environment Programme, to assess and make sense of climate change data from around the world. Thus, the IPCC’s Task Force on National GHG Inventories generates and deploys a methodology to make sense of worldwide GHG emission inventory reports.

Information Gathering

Emissions inventories are variously constructed according to organizational needs. The EPA’s National Emissions Inventory (NEI) is designed to list and assess point-source information from polluting sites within the United States that generate approximately 10 tons per year or more of a single HAP or generate approximately 25 tons per year or more of a combination of HAPs. The NEI includes additional information from nonpoint, on-road, nonroad, event, and facility sources. The EPA gathers its information on 188 pollutants by requiring state, local, and tribal groups to collect data where particulate matter and gases included in the list are known to be generated. Energy generation facilities, factories, and other polluters are targeted, and local groups measure particulate and gas outputs, matching those data with location-based information such as facility names, stack numbers, heights, diameters, temperatures, velocities and flows, pipe locations, and the facilities’ latitude-longitude coordinates.

The NEI gathers additional information, such as estimates from facility construction codes, to account for missing or incomplete data. The goal is for the emissions inventory to demonstrate regional and aggregate growth, nongrowth, or decline in terms of the particulate and gaseous output in regional locations.

Emissions inventories are generally guided by a set of reporting instructions crafted by collecting organizations. The NEI provides particular instructions for how local agencies should gather information for source point and nonpoint sites and now requires reporting agencies to submit information using extensible markup language (XML) for online data manipulation. The International Council for Local Environmental Initiatives (ICLEI) has generated an emissions template and database with a best practices suggestion for organizations to engage baseline assessments, to develop emissions targets, and to implement policies for achieving those targets guided by inventory assessments.

Emissions inventories account for a region’s or municipality’s pollution output, although they are sometimes voluntary and can vary in their purview. GHG emissions inventories account for some gases and air quality issues that go beyond the EPA-required NEI mandates. The voluntary ICLEI is used by more than 500 U.S. municipalities because it takes seriously the output of fuels and other air quality issues beyond HAPs and assumes strict guidelines for reporting measurements more often than estimations. Given current international conversations (including post-Kyoto discussions), as well as local corporate and citizen support, future regulatory regimes, both domestic and international, may rely even more on nuanced and precise emissions inventories.

The United Nations’ Task Force on Emission Inventories and Projections (TFEIP) is organized into expert panels on combustion and industry, transport, agriculture and nature, and projections. In this way, the TFEIP has devised a group of scientists and policy makers to clarify how the United Nations and other world organizations should gather and make sense of natural and anthropogenic emissions reports. The European Environment Agency, for instance, uses the TFEIP’s expert panels as a kind of quality control for methodology and data collection guidelines for emissions inventories. The current trend of emissions inventories usage foretells a future in which they are used with more frequency. As nation-states and intergovernmental groups continue to seek global agreement regarding the constraints of air quality and global warming, this important tool will grow in data-gathering scope and complexity to satiate policy and compliance appetites.

Bibliography

"Air Toxics Screening Assessment." Environmental Protection Agency, 4 May 2024, www.epa.gov/AirToxScreen. Accessed 30 July 2024.

"Clearinghouse for Inventories and Emissions Factors (CHIEF)." Environmental Protection Agency, 31 May 2024, www.epa.gov/chief. Accessed 30 July 2024.

“Convention on Long-Range Transboundary Air Pollution.” US State Department, www.state.gov/key-topics-office-of-environmental-quality-and-transboundary-issues/convention-on-long-range-transboundary-air-pollution/. Accessed 30 July 2024.

Montero, Juan-Pablo. “Tradable Permits With Incomplete Monitoring: Evidence From Santiago’s Particulate Permits Program.” In Moving to Markets in Environmental Regulation: Lessons From Twenty Years of Experience, edited by Jody Freeman and Charles Kolstad. New York: Oxford University Press, 2007.

Yienger, James. “Local Government Lessons on Emissions Inventories: Federal Managers Can Learn From Local Governments and ICLEI-Local Governments for Sustainability, Which Has Pioneered Processes for Greenhouse Gas Emissions Inventories.” The Public Manager 37 (2008).