The Air Emissions Guide to USAF Transitory Sources (Transitory Source Guide) provides recommended methodologies and emission factors used to calculate emissions
for Transitory sources of pollutant emissions commonly found at USAF installations. Transitory sources of emissions are those that are non-routine and/or seasonal
sources (which may be stationary, mobile, or neither) that are short-term in nature. The sources included in this guide include: bulk storage tank cleaning, seasonal equipment,
fuel spills, hot mix asphalt plants, prescribed burns, wild fires, construction, site restoration/remediation, and land use changes.
Transitory sources have historically often been erroneously included in stationary or mobile source air emission inventories, though these sources should only be accounted for
in evaluating potential air quality impacts of proposed actions under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA); National Environmental
Policy Act (NEPA); General Conformity; etc.. The pollutants addressed within this guide include criteria pollutants, Hazardous Air Pollutants (HAPs), Volatile Organic Compounds
(VOCs), and greenhouse gases (GHGs). The August 2018 guide supersedes all prior versions of the Transitory Source Guide; older versions of this document are considered obsolete.