Environmental Engineering Reference
In-Depth Information
Picture 8.1
A combine filling a grain wagon pulled by a tractor. Both are mobile sources of air emissions.
Courtesy Environmental Protection Agency.
On-road mobile sources include passenger cars, trucks (light-duty and heavy duty), buses,
and motorcycles. Nonroad mobile sources comprise recreational off-road vehicles, construction
equipment, industrial equipment (e.g., forklifts), lawn and garden equipment, farm equipment
(e.g., tractors, combines, and sprayers), logging equipment (e.g., chainsaws and shredders),
commercial equipment (e.g., generators, pumps, and air compressors), aircrafts, ground
support equipment used in airport operations, marine vessels (both recreational and
commercial), locomotives, and railway maintenance equipment. In addition to GHGs, mobile
sources release carbon monoxide, VOCs, nitrogen oxides, sulfur dioxides, particulate matter
(particularly from diesel engines), and toxic compounds such as benzene, formaldehyde, and
acetaldehyde. Pollution from mobile sources contributes at local, regional, and global scales.
Stationary sources are fixed in place. The most common stationary sources of air pollution
are oil refineries, chemical-processing facilities, power plants, manufacturing facilities, and
food-processing plants. Pollutants emitted by stationary sources are the result of combustion
of fuel or losses from industrial processes. Emission may come from several emission points
such as smokestacks, storage tanks, equipment leaks, process wastewater, loading/unloading
stations, and process vents.
In the case of stationary sources, the pollutants are emitted at specific points it is called “point
source” emissions (e.g., a smokestack or a storage tank). When the emission of several small
sources contributes to compromising the air quality in a region it is called an “area source type of
emission” (“Sources of pollutants in the ambient air,” n.d.). The difference between point source
and area source is dictated by emission thresholds established by governmental agencies.
Primary and secondary pollutants
Primary pollutants are those emitted directly from identifiable sources of pollution, being the
most important sulfur dioxide, carbon monoxide, nitric oxide (NO), nitrogen dioxide (NO
2
),
nitrous oxide, ammonia, methane, VOCs, and particle matter (“Sources of pollutants in the
ambient air,” n.d.).
