1.5 How is the NEI created?
The “Air Emissions Reporting Rule” (AERR) is the regulation that requires state and local agencies to submit CAP emissions, and the Emissions Inventory System is the data system used to collect, QA, and compile those submittals as well as EPA augmentation data. Most S/L/T air agencies also provide voluntary submissions of HAP emissions. The 2008 NEI was the first inventory compiled using the AERR, rather than its predecessor, the Consolidated Emissions Reporting Rule (CERR). The 2020 NEI is the fifth AERR-based inventory, and improvements in the 2020 NEI process reflect lessons learned by the S/L/T air agencies and EPA from the prior NEI efforts. The AERR requires agencies to report all sources of emissions, except fires and biogenic sources. Reporting of open fire sources, such as wildfires, is encouraged, but not required. Sources are divided into large groups called “data categories”: stationary sources are “point” or “nonpoint” (county totals) and mobile sources are either onroad (cars and trucks driven on roads) or nonroad (locomotives, aircraft, marine, off-road vehicles and nonroad equipment such as lawn and garden equipment).
The AERR has emissions thresholds above which States must report stationary emissions as “point” sources, with the remainder of the stationary emissions reported as “nonpoint” sources.
The AERR changed the way these reporting thresholds work, as compared to the CERR, by changing these thresholds to “potential to emit” thresholds rather than actual emissions thresholds. In both the CERR and the AERR, the emissions that are reported are actual emissions, despite that the criteria for which sources to report is now based on potential emissions. The AERR requires emissions reporting for point sources every year, with additional requirements every third year in the form of lower point source emissions thresholds, and 2020 is one of these third-year inventories.
Table 1.1 provides the potential-to-emit reporting thresholds that applied for the 2020 NEI cycle. “Type B” is the terminology in the rule that represents the lower emissions thresholds required for point sources in the triennial years. The reporting thresholds are sources with potential to emit of 100 tons/year or more for most criteria pollutants, with the exceptions of CO (1000 tons/year), and, updated starting with the 2014 inventory, Pb (0.5 tons/year, actual emissions). As shown in the table, special requirements apply to nonattainment area (NAA) sources, where even lower thresholds apply. The relevant ozone (O3), CO, and PM10 nonattainment areas that applied during the year that the S/L/T agencies submitted their data for the 2020 NEI are available on the “Nonattainment Areas for Criteria Pollutants (Green Book) web site”. Note that while the AERR establishes the minimum requirements for State and local air agencies to report their stationary sources as discrete point sources, many agencies have gone beyond those minimums for many years past, i.e., they report many smaller-emitting sources as discrete point sources.
| Pollutant | Type B Source Thresholds | Thresholds within Nonattainment Areas |
|---|---|---|
| (1) SO2 | ≥100 | ≥100 |
| (2) VOC | ≥100 | O3 (moderate) ≥ 100 |
| (2) VOC | ≥100 | O3(serious) ≥ 50 |
| (2) VOC | ≥100 | O3 (severe) ≥ 25 |
| (2) VOC | ≥100 | O3(extreme) ≥ 10 |
| (3) NOx | ≥100 | ≥100 |
| (4) CO | ≥1000 | O3 (all areas) ≥ 100 |
| (4) CO | ≥1000 | CO (all areas) ≥ 100 |
| (5) Lead | ≥0.5 (actual) | ≥0.5 (actual) |
| (6) Primary PM10 | ≥100 | PM10 (moderate) ≥100 |
| (6) Primary PM10 | ≥100 | PM10 (serious) ≥70 |
| (7) Primary PM2.5 | ≥100 | ≥100 |
| (8) NH3 | ≥100 | ≥100 |
Based on the AERR requirements, S/L/T air agencies submit emissions or model inputs of point, nonpoint, onroad mobile, nonroad mobile, and fires emissions sources. With the exception of California, reporting agencies were required to submit model inputs for onroad and nonroad mobile sources instead of emissions. For the 2020 NEI, all these emissions and inputs were required to be submitted to the EPA per the AERR by December 31, 2021 (with an extension given through January 15, 2022). Once the initial reporting NEI period closed, the EPA provided feedback on data quality such as suspected outliers and missing data by comparing to previously established emissions ranges and past inventories. In addition, the EPA augmented the S/L/T data using various sources of data and augmentation procedures. This documentation provides a detailed account of EPA’s quality assurance and augmentation methods.