- Emissions from Point Sources
- Emissions from Non-Point Sources
Point Source Emissions
Point sources include industrial and nonindustrial stationary
equipment or processes considered significant sources of air
pollution emissions. A facility is considered to have significant
emissions if it emits about one ton or more in a calendar year.
Examples of point sources include industrial and commercial
boilers, electric-utility boilers, turbine engines, wood and pulp
processers, paper mills, industrial surface coating facilities,
refinery and chemical processing operations, and petroleum storage
tanks. Area sources that may fall under the “point
source” definition are piping leaks, industrial wastewater
treatment ponds, rock and quarry operations, and tank farms.
Insignificant point sources are included by category in the area
source inventory.
The most accurate method for determining the amount of emissions
produced by a facility is with continuous emissions monitoring.
However, this is expensive and not always practicable. Emissions
are estimated using a variety of methods. Standard methods of
estimating point source emissions are available from the U.S.
Environmental Protection Agency in the Compilation of Air
Pollutant Emission Factors, Volume I, also known as AP-42.
Other methods include stack testing, equipment vendor test data,
material balances such as for surface coating, or TCEQ-approved
permit factors. If no other method is available, then the best
engineering judgment must be used.
Facilities report point source emissions to the TCEQ for the
calendar year and the data are stored in the Point Source Database.
Data are available for use by TCEQ staff, the EPA, state and
federal legislators, air pollution researchers, public interest
groups and the general public.
Point Source Emissions Data
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Emissions from Non-Point Sources
On-Road Mobile Sources
Emissions from on-road mobile sources are estimated using a
sophisticated model called MOBILE, which was developed by the EPA.
MOBILE calculates an emissions factor for mobile sources using a
set of complex mathematical equations that require several user
input values.
Vehicles are segregrated into eight vehicle classes, with MOBILE
generating an emissions factor for each class and a composite
emissions factor representing all classes.
On-Road Mobile Source Vehicle Classes
- Light-duty gasoline vehicles (LDGV)
- Light-duty gasoline trucks up to 6,000 pounds gross vehicle
weight (LDGT1)
- Light-duty gasoline trucks from 6,001 to 8,500 pounds gross
vehicle weight (LDGT2)
- Heavy-duty gasoline vehicles with more than 8,500 pounds gross
vehicle weight (HDGV)
- Light-duty diesel vehicles (LDDV)
- Heavy-duty diesel vehicles with more than 8,500 pounds gross
vehicle weight (HDDV)
- Motorcycles (MC)
- Light-duty diesel-powered trucks (LDDI)
After an emissions factor is generated for each vehicle class,
the factor is then used in conjunction with the vehicle miles
traveled (VMT) estimates, which were developed with the Texas
Highway Performance Monitoring System (HPMS) data set for that
selected area. This combination determines the contribution of
emissions from mobile sources in a city, county, or state. VMT data
is maintained by the Texas
Department of Transportation. 
The HPMS Program produces VMT estimates for various roadway
types categorized into two major population areas—urban and
rural.
| Roadway Types |
Urban
Interstate
Other freeways and expressways
Other principal arterial
Minor arterial
Collector
Local |
Rural
Interstate
Other principal arterial
Minor arterial
Major collector
Minor collector
Local |
In Texas, emissions from mobile sources are estimated on a
county-wide basis. With a few exceptions nationwide, on-road mobile
sources constitute the largest single source category of air
pollution.
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Non-Road Mobile Sources
Nonroad mobile sources include a wide variety of internal
combustion engines not associated with highway vehicles. Emissions
calculation methodology is as varied as the categories themselves.
A federal computer model using engine types and landing-takeoff
cycles is used to calculate most aircraft emissions. Actual fuel
usage and track mileage are applied to determine locomotive
emissions. Data on ship and barge traffic is used to calculate
emissions from ocean vessels.
Nonroad Mobile Source Categories
Aircraft:
Commercial
Military
General:
Locomotives
Vessels (ships and barges) |
Small Engines:
Lawn and garden
Airport support vehicles
Recreational marine
Light commercial
Industrial construction
Agricultural logging
|
The EPA developed emissions factors for a lengthy list of small
engine categories, which included research on individual engines
and fuel types. Included in this category are two major emissions
sources—lawn mowers and recreational boat engines.
Nonroad Mobile Small Engine Categories
|
Lawn and Garden:
Trimmers/edgers/brush cutters
Lawn mowers
Leaf blowers/vacuums
Rear engine riding mowers
Front mowers
Chainsaws, 4 horsepower (HP)
Shredders, 5 HP
Tillers, 5 HP
Lawn and garden tractors
Wood splitters
Snowblowers
Chippers/stump grinders
Commercial turf equipment
Other lawn and garden equipment
Airport Support:
Aircraft support equipment
Terminal tractors
Recreational Vehicles:
All terrain vehicles
Minibikes
Off-road motorcycles
Golf carts
Snowmobiles
Specialty vehicle carts
Recreational Marine:
Vessels with inboard engines
Vessels with outboard engines
Vessels with stern drive engines
Sailboat auxiliary inboard engines
Sailboat auxiliary outboard engines
Light Commercial:
Generator sets, 50 HP
Pumps, 50 HP
Air compressors, 50 HP
Gas compressors, 50 HP
Welders, 50 HP
Pressure washers, 50 HP
Industrial:
Aerial Lifts
Forklifts
Sweepers/scrubbers
Other general industrial equipment
Other material handling equipment
|
Construction:
Asphalt pavers
Tampers/rammers
Plate compactors
Concrete pavers
Rollers
Scrapers
Paving equipment
Surfacing equipment
Signal boards
Trenchers
Bore/drill rigs
Excavators
Concrete/industrial Saws
Cement and mortar mixers
Cranes
Graders
Off-highway trucks
Crushing/process equipment
Rough terrain forklifts
Rubber tired loaders
Rubber tired dozers
Tractors/loaders/backhoes
Crawler tractors
Skid steer loaders
Off-highway tractors
Dumpers/tenders
Other construction equipment
Agricultural:
2-wheel tractors
Agricultural tractors
Agricultural mowers
Combines
Sprayers
Balers
Tillers, 5 HP
Swathers
Hydro power units
Other agricultural equipment
Logging:
Chainsaws, 4 HP
Shredders, 5 HP
Skidders
Fellers/bunchers
|
Non-Road Mobile Source Emissions Data
1999 Non-Road Mobile Source Emissions Data
(PDF) (2.62MB)
1999 Detailed Non-Road Mobile Source Emissions
Data (PDF) (2.09MB)
2002 Non-Road Mobile Source Emissions Data
(PDF) (732KB)
2002 Detailed Non-Road Mobile Source Emissions
Data (PDF) (2.21MB)
Non-Road Assessment Tool & Estimator (NATE)
Guide (PDF) (1121KB)
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Area Sources
Area source inventories generally report emissions by categories
rather than by individual source; a common method in reporting
point source emissions. Area source emissions are calculated by
various methods and depend on the type of data available for each
category. For example, whenever fuel use and materials data are not
available, employee and county population numbers are used with
established emission factors to calculate emissions. Emissions are
calculated and reported on a county-wide basis.
Major categories of area sources are:
- Stationary source fuel combustion such as residential fuel
combustion
- Solvent use (e.g., small surface coating operations)
- Product storage and transport distribution (e.g.,
gasoline)
- Light industrial/commercial sources
- Agriculture (e.g., feedlots, crop burning)
- Waste management (e.g., landfills)
- Miscellaneous area sources (e.g., forest fires, wind erosion,
unpaved roads)
The following table gives a more complete list of area sources
by category.
|
Product storage and transport distribution:
Oil and gas production
Oil and gas production—offshore
Aircraft refueling
Marine vessel loading losses
Leaking underground tanks
Catastrophic/accidental releases
Service stations:
Vehicle refueling
Tank truck unloading
Tank trucks in transit
Tank breathing losses
Other (spillage)
Solvent use:
Barge, tank, tank truck, rail car, drum cleaning
Consumer/commercial solvent use
Surface cleaning (degreasing)
Dry cleaning
Graphic arts
Cutback asphalt
Emulsified asphalt
Waste management:
Municipal waste landfills
Municipal wastewater treatment (POTW)
Industrial wastewater treatment
Wastewater package plants
Light industrial and commercial sources:
Commercial bakeries
Breweries
Wineries
Distilleries
Agriculture and miscellaneous area sources:
Pesticide application
Orchard heaters
Agricultural burning
Prescribed burning
Structure fires
Forest fires
Slash burning
Open burning
|
Painting operations:
Architectural coatings
Auto refinishing
Traffic markings
Furniture fixtures
Metal containers
Automobiles (new)
Machinery and equipment
Appliances
Other transportation equipment
Sheet, strip, and coil
Factory finished wood
Electrical insulation
Other product coatings
High-performance maintenance
Marine coatings
Other special purpose coatings
Stationary source fuel combustion:
Fuel oil—residential
Fuel oil—commercial/distillate
Fuel oil- commercial/residual
Fuel oil—industrial/residual
Coal—residential
Coal—commercial
Coal—industrial
Natural gas—residential
Natural gas—commercial
Natural gas—industrial
LPG—residential
LPG—commercial
LPG—industrial
Wood—residential
|
Area Source Emissions Data
1999 Area Source Emissions Data (PDF)
(3.66MB)
1999 Detailed Area Source Emissions Data (PDF)
(3.74MB)
2002 Area Source Emissions Data (PDF)
(781KB)
2002 Detailed Area Source Emissions Data (PDF)
(860KB)
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Biogenic Sources
Biogenic emissions account for 30 percent of all the volatile
organic compounds (VOCs) emitted in urban areas in the eastern half
of Texas. For the purposes of photochemical modeling, biogenic VOC
emissions are estimated using a computer model that takes into
account the species of trees present, the density of their foliage,
the temperature and solar radiation on the day in question, and the
distribution of vegetation throughout the modeling domain. It is
important to measure these parameters accurately if the biogenics
inventory is to be correct. The TCEQ has hired specialists to
measure some of these variables in north-central and southeastern
Texas.
Most plants emit some VOCs, but the largest emitters are oaks,
pines, sweet gums, eucalypti, and poplars. Some VOCs are easily
detected by their aroma. Pines, sycamores, and eucalypti emit
fragrant monoterpenes, while other VOCs—such as
isoprene—are not as aromatic.
Isoprene is a byproduct of photosynthesis. Scientists still
debate the purpose of its emission but some evidence suggests that
plants can cope better with heat if isoprene is present. Because it
is generated by photosynthesis, isoprene emissions are not
generated at night.
Monoterpenes are known as “essential oils.” There is
solid evidence that plants make monoterpenes, which are found in
small reservoirs in the leaves or needles of plants, to ward off
herbivores. When an insect feeds on the leaf, the monoterpenes are
released and can adversely affect the insect’s health. Because
the monoterpenes are always present in the leaves, their emission
rate depends mostly on the temperature. Higher temperatures will
evaporate larger amounts into the atmosphere.
There are a few other important organic compounds emitted by
plants. Alcohols are often emitted by damaged vegetation; there is
some evidence that these alcohols act as an antiseptic. A few
recent studies suggest that alkenes are also emitted by some
plants.
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