Measuring emissions at this lower level has the potential to also capture ambient emissions surrounding your facility. There are naturally occurring particulate emissions from atmospheric chemical reactions as well as various regional environmental issues such as wildfires or surrounding facilities.
A “major source” is one that has the potential to emit, 10 tons per year of any HAP, or 25 tons per year or more of any combination of HAPs. “Area sources” have potential HAP emissions below this threshold. If you are a “major source” and have made changes to reduce your HAP emissions below the “major source” threshold, you may qualify as an “area source” with EPA’s withdrawal of the “Once in, Always In” policy.
Fugitive emissions are emissions that could not reasonably pass through a stack, chimney, vent, or similar opening. If EPA repeals the 2008 rule, all existing major stationary sources to include fugitive emissions in determining whether a project is a major modification.
The EPA’s Minor New Source Review (NSR) program applies to a new minor source in facilities that can potentially emit pollutants in amounts less than what are considered "significant thresholds" and/or a minor modification at a major source in both attainment and non attainment areas. (If the air quality in a geographic area meets or exceeds the national standard, it is called an attainment area; areas that don't meet the national standard are called non attainment areas.) The program requirements include new air pollution sources or modifications at existing sources that must comply with any emissions control measures required by the state in which the facility operates.