What is the National Emissions Inventory (NEI) and how it can be useful to you?
What is the NEI:
The NEI is a comprehensive and detailed estimate of air emissions of criteria pollutants, criteria precursors, and hazardous air pollutants from air emissions sources. The NEI is released every three years based primarily upon data provided by State, Local, and Tribal air agencies for sources in their jurisdictions and supplemented by data developed by the US EPA.
The NEI homepage can be found here.
What is included in the NEI:
The EPA breaks down each NEI into several categories:
- Documentation
- Data Summaries
- Data Queries
- Facility Mapping
- Emissions Modeling Files
- Documentation:
Although each report is different, the NEI documentation will typically include:
- An NEI report which provides an overview of the air pollution emissions.
- A Technical Support Document for the report containing details for each NEI report such as where the data came from, how the data was used, and methods used to estimate emissions.
- Supporting Data and Summaries which grants access to the actual data used in the NEI report.
- An interactive report summarizing what the report contains and allows the user to interact with data such as national and state trends for air emissions.
- Data Summaries:
The NEI has five classifications of sources, NEI point sources, NEI nonpoint sources, NEI onroad sources, NEI nonroad sources, and NEI “event” sources. A definition of each of the sources can be found here. The data summaries portion of the NEI contains the actual data for each source, source type, and pollutant in excel format.
- Data Queries:
The Data Queries section of the report allows the generation of custom data files containing subsets of the summaries described above. These files can be tailored to the national, state, or tribal level with further filtering into specific pollutants and sectors (ex. agriculture, fuel combustion, etc.)
- Facility Mapping:
Facility mapping allows the user to search for facilities that emit the selected pollutant within a certain state. The output is a map with pins showing the location of each facility emitting the stated pollutant.
How the NEI can be useful:
The NEI is a wealth of information collected in one convenient location, enabling the user to easily search and be kept up to date on matters relating to emission trends both on a state and national level, emissions factors, and how the EPA reviews and reacts to the latest information.
A great example of how the NEI can impact emissions calculations can be seen in the 2014 NEI. As mentioned above, the EPA will periodically review emissions factors. In the 2014 NEI, the EPA reviewed (amongst many other things) the emissions factor for Particulate Matter (PM) for Natural Gas combustion. The findings state that:
“The method is not final but some preliminary data was available and the data showed the current AP42 factors were off by a factor of 10 or 20.”
The 2014 NEI then proceeds to provide a list of updated emission factors for PM in Natural Gas combustion, stating that:
“These emission factors can be considered for inventory calculations when there are no site-specific data available.”
Depending on the usage of natural gas combustion at a facility, the update to the emission factor could reduce the particulate matter emissions by a factor of 10 to 20.
Such data can be used and should be considered when building emissions inventories.
Carter Venable