Appendix 6: Description of "Non-Road" Transportation Sources from the EPA's National Emissions Inventory (NEI)
Source: EPA’s National Emissions Inventory
The U.S. EPA’s National Emissions Inventory (NEI) is a nationwide compilation of air pollutant emission estimates. Pollutants included in the NEI are criteria air pollutants (CAPs), precursors to CAPs, and hazardous air pollutants (HAPs). In addition, the NEI houses emission estimates for greenhouse gases (GHGs) for select sectors. Currently, the NEI is compiled on 3-year cycles, with the 2020 NEI being the most recent release. Staff at the EPA collaborates with state, local, and tribal (SLT) air agencies to estimate emissions for each NEI, with additional data coming from other programs, such as the Toxics Release Inventory (TRI) and the Greenhouse Gas Reporting Program (GHGRP). Emission estimates are compiled within the Emission Inventory System (EIS) and subsequently selected using a hierarchical approach to generate a complete inventory. Additional information on the latest NEI release can be found here.
Emission sources in the NEI are consolidated into four data categroies: onroad mobile, nonroad mobile, nonpoint, and point. Onroad mobile sources include emissions from motorized vehicles that normally operate on public roadways. This includes passenger cars, motorcycles, minivans, sport-utility vehicles, light-duty trucks, heavy-duty trucks, and buses. The sector includes emissions generated from parking areas, emissions from short-duration idle during pickups / deliveries, emissions from vehicles when they start, and emissions while the vehicles are moving. The sector also includes “hoteling emissions, which refers to the time spent idling in a diesel long-haul combination truck during federally mandated rest periods of long-haul trips.
The mobile nonroad equipment data category includes all mobile source emissions that do not operate on roads, excluding commercial marine vehicles, railways, and aircraft. These sources included included in this category are construction, agriculture, industrial, lawn & garden (commercial and residential), commercial, logging, railroad support (excluding locomotives), recreational vehicles, recreational marine (pleasure craft, excluding commercial marine vessels; CMVs), and underground mining.
The nonpoint emissions category includes biogenic emissions, fires (wildfires, prescribed burning, and agricultural field burning), and all other stationary sources that aren’t covered in the point category. These sources are all reported at the county-level, though some sources such as shipping lanes and ports are more finely resolved to the county / shape identifier (ID) (polygon) level. In addition, some nonroad mobile sources, such as trains and commercial marine vessels, reside within the nonpoint data category.
The point source emissions category is composed of individual facilities, usually at specific latitude / longitude coordinates, rather than as county or tribal aggregates. These facilities include large energy and industrial sites, such as electric generating utilities(EGUs), portland cemet manufacturing plats, petroleum refineries, natural gas compressor stations, and facilities that manufacture pulp and paper, automobiles, machinery, chemicals, fertilizers, pharmaceuticals, glass food products, and other products. Additionally, smaller points sources are included voluntarily by some SLT agencies, and can include small facilities such as crematoria, dry cleaners, and gas stations. The point source data category also includes emissions from the landing and take-off portions of aircraft operations, the ground support equipment at airports, and locomotive emissions within railyards.