Aviation Emissions and Air Quality Handbook  91$_{ }$ Finding of No Significant Impact (FONSI) - A FONSI is a document which briefly presents  evidence of why Federal agency has determined that a proposed action, not categorically excluded, will not have a significant impact on the environment. The Federal Action - Actions with effects that may be major and potentially subject to Federal  control and responsibility. Federal actions tend to fall into four categories: adoption of official  policy, adoption of formal plans, adoption of programs and approval of projects, approved by permit or other regulatory decision. See 40 CFR 1508.16 for additional information.  Environmental Impact Statement (EIS) - An EIS is a detailed, concise public document  required for major Federal actions likely to have significant effects on the human environment.  The document may be directly prepared, without first doing an EA, if the action will significant environmental impacts. An EIS provides the public and decision makers with clear,  written documentation of potential significant environmental effects of the proposed action, and  reasonable alternatives including the no action alternative.  Environmental Assessment (EA) - A concise public document that provides sufficient data,  evidence, and analysis to determine if Federal agency should prepare an EIS for an action issue a FONSI. An EA is not necessary in cases where the Federal agency has decided to prepare  an EIS. An EA can be prepared at any time to aid agency decision making.  Emissions and Dispersion Modeling System (EDMS) - A model designed to assess the air  quality impacts of airport emission sources, particularly aviation sources, which consist aircraft, APUs, GSE, ground access vehicles, and stationary sources.  Emission Inventory - A complete list of sources and rates of pollutant emissions within specific area and time interval.  Emission Factor - The rate at which pollutants are emitted into the atmosphere by one source or  a combination of sources.  Dispersion - The process by which atmospheric pollutants disseminate due to wind and vertical  stability.  Direct Emissions - Direct emissions are those caused by or initiated by the implementation  and/or operation of an action, and that occur at the same time and place as the action.  Direct Effect - An effect that is caused by the implementation and/or operation of an action that  occurs at the same time and place. These type of effects are also often referred to as primary  effects.  De minimis  - So small as to be negligible or insignificant. If an action has  de minimis  emissions  (Conformity Rule 40 CFR 93.153c), then a conformity determination pursuant to the CAA of  1990 is not required.  Criteria Pollutants - The six pollutants listed in the CAA that are regulated by the EPA through  the NAAQS because of their health and/or environmental effects. They are: nitrogen dioxide  (NO$_{2}$), sulfur dioxide (SO$_{2}$), carbon monoxide (CO), ozone (O$_{3}$), particulate matter (PM) which  is segregated into two size ranges: equal to or less than 10 microns in diameter (PM$_{10}$) and equal  to or less than 2.5 microns in diameter (PM$_{2.5}$), and lead (Pb).  effects influence a reservation, an Indian Tribe. By agreement with the lead agency, an Indian  Tribe may become a cooperating agency. 