Emissions Inventories are important tools, enabling us to better comprehend the types and quantities of pollutants that are emitted to the air we breathe over a specific time period. In order for the Air Division to create these inventories, it is necessary to do the following:
- Identify important air pollution emission sources
- Determine the specific pollutants that are emitted from these sources
- Use high quality emission factors (EFs), such as those compiled by the U.S. Environmental Protection Agency (EPA), documented in peer-reviewed scientific studies, generated through specific source testing, or obtained from other reliable sources. Some examples of emissions factors include “grams of benzene emitted per mile traveled by a light duty gasoline vehicle”, or “pounds of particulate matter emitted per ton of wood burned in an EPA-certified woodstove”.
- Establish an estimate of "activity" (for example: how many miles were traveled by the vehicle in the specified year, or how many tons of wood were burned in the woodstove during that year)
A simple equation for estimating emissions can be expressed as:
E = A x EF X (1-ER/100)
where: E = emissions;
A = activity rate; EF = emission factor;
and ER = overall emission reduction efficiency, %
In general, "sources" fall into one of the following categories:
Point: Refers to emissions that can be traced to a specific concentrated point (such as a factory, power plant, etc.) This category is extensively inventoried through the Air Division's annual Point Source Registration Program. According to U.S. EPA definition, however, most of Vermont's "Point Sources" would be considered "Area / Nonpoint Sources" for annual emissions of certain pollutants. For example, if potential emissions from a particular factory are less than the defined threshold, it will be classified as an Area Source by EPA. For more information, please reference EPA’s Air Emissions Reporting Requirements (AERR) published in the Federal Register.
Area / Nonpoint: Stationary sources of air pollution for which it is difficult to attribute emissions to a concentrated point (such as emissions from agricultural livestock, illegal open burning of trash, residential heating, etc.). In some cases, this category may include "Point Sources" having emissions below a certain defined threshold. (see Point above)
Mobile: Includes both Onroad (automobiles, trucks, buses, motorcycles, etc.) and Nonroad (construction equipment, lawn and garden equipment, ATVs, snowmobiles, motorboats, etc.)
Biogenic: Natural sources of air pollution (ex: Isoprene emitted from plants, Ammonia emitted from the soil, etc.)
A comprehensive emissions inventory known as the National Emissions Inventory (NEI) is prepared every three years by the U.S. EPA in collaboration with the State of Vermont, and other state, local, and tribal air agencies across the U.S. The NEI is a detailed database of both criteria and hazardous air pollutant emissions estimates from all quantifiable air emissions sources. Additional general information about emissions inventories, as well as actual NEI emissions data can be accessed at: http://www.epa.gov/air-emissions-inventories.
Questions or comments? - contact Jeff Merrell