The Air Emissions Guide to USAF Transitory Sources (Transitory Source Guide) provides recommended methodologies and emission factors for
calculating actual emissions for the most common types of transitory sources found at USAF installations. Transitory sources are non-routine
and/or seasonal sources (may be stationary, mobile or neither) that are short-term in nature. Transitory sources include: bulk storage tank cleaning,
seasonal equipment, fuel spills, hot mix asphalt plants, prescribed burning, wild fires, all sources associated with construction, and all sources
associated with site restoration/remediation. While historically transitory sources have often been erroneously included in stationary or mobile
source air emission inventories, transitory source emissions should generally only be accounted for in evaluating potential air quality impacts
of proposed action under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA); National Environmental Policy Act
(NEPA), General Conformity, etc. The pollutants addressed in the guide include criteria pollutants, hazardous air pollutants (HAPs),
Volatile Organic Compounds (VOCs), and greenhouse gases (GHGs). The September 2017 guide is the most current version of the Transitory Source Guide;
all other versions are superseded and considered obsolete.