new timberlands Air pollution dispersion terminology
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(PD) Commander Mark Moran, NOAA Corps.
Flare in Motiva refinery west of New Orleans.
Air pollution dispersion terminology describes the words and technical terms that have a special meaning to those who work in the field of air pollution dispersion modeling.
Governmental environmental protection agencies (local, state, province and national) of many countries have also adopted and used much of the terminology in their laws and regulations regarding air pollution control.
It should be noted that some of the words and technical terms in Air pollution dispersion terminology quite often have other special meanings when used in fields of activity other than air pollution dispersion modeling.
Buoyant plumes Plumes which are lighter than air because they are at a higher temperature and lower density than the ambient air which surrounds them, or because they are at about the same temperature as the ambient air but have a lower molecular weight and hence lower density than the ambient air. For example, the emissions from the flue gas stacks of industrial furnaces are buoyant because they are considerably warmer and less dense than the ambient air. As another example, an emission plume of methane gas at ambient air temperatures is buoyant because methane has a lower molecular weight than the ambient air.
Dense gas plumes Plumes which are heavier than air because they have a higher density than the surrounding ambient air. A plume may have a higher density than air because it has a higher molecular weight than air (for example, a plume of carbon dioxide). A plume may also have a higher density than air if the plume is at a much lower temperature than the air. For example, a plume of evaporated gaseous methane from an accidental release of liquefied natural gas (LNG) may be as cold as 161 C.
Passive or neutral plumes Plumes which are neither lighter or heavier than air. It also assumes that the air pollutants inside the box are homogeneously distributed and uses that assumption to estimate the average pollutant concentrations anywhere within the airshed. Although useful, this model is very limited in its ability to accurately predict dispersion of air pollutants over an airshed because the assumption of homogeneous pollutant distribution is much too simple.
Gaussian model The Gaussian model is perhaps the oldest (circa 1936)  and perhaps the most commonly used model type. It assumes that the air pollutant dispersion has a Gaussian distribution, meaning that the pollutant distribution has a normal probability distribution. Gaussian models are most often used for predicting the dispersion of continuous, buoyant air pollution plumes originating from ground level or elevated sources. Gaussian models may also be used for predicting the dispersion of non continuous air pollution plumes (called puff models). The primary algorithm used in Gaussian modeling is the Generalized Dispersion Equation For A Continuous Point Source Plume.
Lagrangian model a Lagrangian dispersion model mathematically follows pollution plume parcels (also called particles) as the parcels move in the atmosphere and they model the motion of the parcels as a random walk process. The Lagrangian model then calculates the air pollution dispersion by computing the statistics of the trajectories of a large number of the pollution plume parcels. A Lagrangian model uses a moving frame of reference as the parcels move from their initial location. It is said that an observer of a Lagrangian model follows along with the plume.
Eulerian model a Eulerian dispersions model is similar to a Lagrangian model in that it also tracks the movement of a large number of pollution plume parcels as they move from their initial location. The most important difference between the two models is that the Eulerian model uses a fixed three dimensional Cartesian grid as a frame of reference rather than a moving frame of reference. It is said that an observer of a Eulerian model watches the plume go by. The three most commonly used dense gas models are:
The DEGADIS model developed by Dr. Jerry Havens and Dr. Tom Spicer at the University of Arkansas under commission by the United States Coast Guard and United States Environmental Protection Agency (EPA). 
The SLAB model developed by the Lawrence Livermore National Laboratory funded by the United States Department of Energy, the United States Air Force and the American Petroleum Institute.
The HEGADAS model developed by Shell Oil Company’s research division. Environmental Protection Agency.
Air pollutant emission sources
(PD) Park Service
Before flue gas desulfurization was installed, the emissions from this conventional coal fired power plant in New Mexico contained excessive amounts of sulfur dioxide
The types of air pollutant emission sources are commonly characterized as either point, line, area or volume sources:
Point source A point source is a single, identifiable source of air pollutant emissions (for example, the emissions from a combustion furnace flue gas stack). Point sources are also characterized as being either elevated or at ground level. A point source has no geometric dimensions.