Types of Air Emissions:
Actual emission: The annual 'actual' emissions
which have been estimated or calculated for a plant in the State
Emission Inventory, added to those annual emissions that have been
removed by the application of a control factor.
Allowable emissions: Maximum emissions for a
pollutant that a plant or a source is allowed to discharge
emission into the atmosphere legally.
Potential controlled emission: Pollutant
emissions while operating at the maximum design capacity,
a schedule of 8760 hours per year and the design value of control
efficiency equipment.
Potential uncontrolled emission: Pollutant
emissions while operating at the maximum design capacity and a
schedule of 8760 hours per year.
Types of Air Emission Sources:
Point Sources: The major point source emissions
categories are power plants, industrial boilers, petroleum
refineries, industrial surface coatings and chemical manufacturing
industries. Point sources' emissions are generated from stack
emissions. Since most of the records are kept in AIRS/AFS, the
point sources information is readily available for developing a
control strategies, tracking and implementation of the State
Implementaion Plans (SIP). For SIP inventory purposes, the point
source emission cutoff is 10 tons per year for VOC and 100 tons
per year for Nox and CO sources. For VOC sources emitting 10 tons
per year or more, base year inventory emissions must be determined
from each facility. Emissions information for individual point
sources can be obtain using Envirofacts'
Air Release Query Form
Area sources: Area sources are those emissions
that are too small to be treated as point sources. Area sources'
emissions can be generated from solvents used for surface coating
operation, degreasing, graphic arts, dry cleaning and gasoline
station (tank truck unloading and refueling). Area sources are the
activities where aggregated source emissions information is
maintained for the entire source categories instead of each point
source, and are reported at the county level.
Mobile Sources: Mobile sources are categorized
for highway and off-highway sources. The highway sources include
the automobile, buses truck and other vehicle traveling on local
and highway roads. The emission from highway vehicles represents
one third of the overall national volatile organic compounds (VOC)
and 40 percent of the overall nitric oxide (NOx) emissions.
Highway emissions are calculated using MOBILE models. States
must present highway mobile source emissions by pollutant (VOC,
NOx and CO) and by individual nonattainment county. Off-highway
sources are any mobile combustion sources such as railroads,
marine vessel, off-road motorcycle, snowmobiles, farm, construction,
industrial and lawn/garden equipment. Emissions are determined
based on a source activity variable. Activity levels for each
off-highway category must be developed using EPA guidance documents.
National Emission Trends and Inventories:
The
National Air Pollutant Emission Trends Report document
presents the most recent estimate of national emissions of the
criteria air pollutants. The emissions of each pollutant are
estimated for many different source categories, which collectively
account for all anthropogenic emissions. The Report presents the
total emissions from all 50 states. These estimates are updated
annually. The emission trends are the net effect of many factors,
including changes in the nation's economy and in industrial
activity, technology, consumption of fuels, traffic, and other
activities that cause air pollution. The trends also reflect
changes in emissions as a result of air pollution regulations
and emission controls. These annual reports will serve as a
measure of our nation's progress in reducing air pollution
emissions as a result of mandatory and voluntary controls and
of continuous changes in national activity.
The EPA maintains emission inventory databases for both toxic
and criteria pollutants which are used for air dispersion modeling,
regional strategy development, regulation setting, air toxics
risk assessment, and for developing the emission trends reports.
These data are available from the
National
Emission Inventory Trends website.
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