Area sources are smaller sources of air pollution, such as drycleaners, gas stations, etc. They often lack locational data and site-specific emissions data, so they are treated in exposure estimation models as sources that are distributed in space (i.e., releasing x tons of pollutant per square mile). Emissions levels from area sources are uncertain because they are often derived using various surrogates (such as levels of economic activity, etc.) The definitions of area sources for criteria and hazardous air pollutants are similar but not identical.
AREA SOURCES - HAZARDOUS AIR POLLUTANTS
EPA's National-Scale Air Toxics Assessment defines area sources as pollution sources that generally have smaller emissions on an individual basis than major "point" sources and are often too small or ubiquitous in nature to be inventoried as individual sources. "Area sources" include facilities that have air toxics emissions below the major source threshold as defined in the air toxics sections of the Clean Air Act and thus emit less than 10 tons of a single toxic air pollutant or less than 25 tons of multiple toxic air pollutants in any one year. Area sources include smaller facilities, such as dry cleaners. "Other sources" include sources such as wildfires and prescribed burnings.
NATA does not provide a breakout of more detailed area source categories. NATA does not include information on diesel emissions from point sources.
AREA SOURCES - CRITERIA AIR POLLUTANTS
Scorecard's criteria air pollutant reports are based on EPA's National Emissions Trends database. Definitions of EPA's area source category are provided in its National Air Pollutant Emissions Trends Report, 1900-1996.
To support Clean Air Act regulations, EPA has assigned Source Classification Categories (SCCs) for air pollution generating activities. These classifications are used to develop estimates and projections of air pollution by pollutant type. Presented below is a brief description of the area source categories used by Scorecard:
Stationary Source Fuel Combustion: Industrial and electrical utilities, commercial, and institutional fuel combustion, residential fuel combustion (wood burning fires, gas and charcoal barbecue grills).
Industrial Processes: Construction, mining and quarrying, in-process fuel use.
Solvent Utilization: Surface coating operations, degreasing and commercial dry cleaning, auto body painting and refinishing.
Solvent Storage and Transport: Organic chemical storage, petroleum storage and transport.
Waste Disposal, Treatment and Recovery: Wastewater treatment, open burning and landfills.
Natural Sources: Off-gasing from non-anthroprogenic sources (both biological and geologica).
Miscellaneous Area Sources: Agricultural crop and livestock production, cooling towers and other combustion activities.
ONLINE AREA SOURCE RESOURCES
EPA's Urban Air Toxics Strategy includes proposed emissions reductions efforts for area sources.