Environmental Engineering Reference
In-Depth Information
8 Air Emissions
EMISSIONS WITH LOCAL, REGIONAL, AND GLOBAL IMPACTS
The US Environmental Protection Agency (EPA) defines air emissions as “gases and particles
which are put into the air or emitted by various sources” and are the cause of air pollution. Air
pollution comes from natural and anthropogenic sources and has local, regional, and global
impacts.
Sources of anthropogenic air pollution are both stationary and mobile, including agriculture,
power plants, refineries, industries, waste incinerators, wastewater treatment plants, the use of
chemicals, vehicles and vessels and landfills. The most common pollutants are carbon monoxide
(CO), nitrogen oxides (NOx), ground-level ozone (O
3
), particle matter, sulfur dioxide (SO
2
),
odor, nitrous oxide (N
2
O), ammonia (NH
3
), methane (CH
4
), and volatile organic compounds
(VOCs). Traditionally, carbon dioxide (CO
2
) has not been considered an air pollutant; however,
the EPA has recently included carbon dioxide within the framework of the Clean Air Act and
established regulations for the emission of carbon dioxide, directed at largest emitters such as
power plants and refineries (“EPA sets schedule for CO
2
regulation,” 2011).
At a regional scale, the most significant emissions come from agricultural sources—which
may have local influence as well—and mobile and stationary sources such power plants. The
most ordinary pollutants with regional impact are ammonia, nitrous oxide, nitrogen oxides,
sulfur oxides, VOCs, odor, and particle matter. At the global scale are all the sources that
produce greenhouse gases (GHGs) and stratospheric ozone depletion gases—basically most
of human activities. Emissions include methane, nitrous oxide, halocarbons, and carbon
dioxide, if considered a pollutant.
Mobile versus stationary sources
Mobile sources of pollution are a variety of vehicles, engines, and equipment that move, or
can be moved, from one place to another (“What are mobile sources,” n.d.). There are two
broad subcategories of mobile sources:
1. On-road, or highway, vehicles used for transportation of freight and people.
2. Nonroad vehicles, engines, and equipment used for construction, agriculture,
transportation, recreation, and many other purposes.
