Line source

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North-South Expressway in Malaysia. A roadway can be a line source of air and noise pollution and need not be a straight line. NorthSouth-Expressway.jpg
North–South Expressway in Malaysia. A roadway can be a line source of air and noise pollution and need not be a straight line.

A line source, as opposed to a point source, area source, or volume source, is a source of air, noise, water contamination or electromagnetic radiation that emanates from a linear (one-dimensional) geometry. The most prominent linear sources are roadway air pollution, aircraft air emissions, roadway noise, certain types of water pollution sources that emanate over a range of river extent rather than from a discrete point, elongated light tubes, certain dose models in medical physics and electromagnetic antennas. While point sources of pollution were studied since the late nineteenth century, linear sources did not receive much attention from scientists until the late 1960s, when environmental regulations for highways and airports began to emerge. At the same time, computers with the processing power to accommodate the data processing needs of the computer models required to tackle these one-dimensional sources became more available.

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In addition, this era of the 1960s saw the first emergence of environmental scientists who spanned the disciplines required to accomplish these studies. For example, meteorologists, chemists, and computer scientists in the air pollution field were required to build complex models to address roadway air dispersion modeling. Prior to the 1960s, these specialities tended to work within their own disciplines, but with the advent of NEPA, the Clean Air Act, the Noise Control Act in the United States, and other seminal legislation, the era of multidisciplinary environmental science had begun.

For electromagnetic linear sources, the principal early advances in computer modeling arose in the Soviet Union and USA when the end of World War II and the Cold War were fought partially by progress in electronic warfare, including the technologies of active antenna arrays.

Linear air pollution source

Air pollution levels near major highways and urban arterials are in violation of U.S. National Ambient Air Quality Standards where millions of Americans live or work. Even the interior of a building does not really protect inhabitants from adverse exterior air quality, since the exterior air is the intake supply, and it is well known that indoor air quality is typically worse than exterior air.

A roadway travelled by motor vehicles can be idealized by a line source emitting air pollutants. This mathematical problem was first solved in 1970 by a collaboration of physics, mathematics and computer science. [1] [2] The original theory assumed steady-state traffic conditions and meteorology on a perfectly straight roadway. Currently the models have evolved to treat variable meteorology, time-variant traffic operations and complex roadbed geometries. Current technology allows highway designers and city planners to analyze alternative roadway development plans and assess air quality impacts. The same basic model theory can be applied to airport operations, since the linear source is merely an inclined line. In the early 1970s these ESL models were refined into area source models to account for the finite width of the roadway.

Linear noise source

The New Jersey Turnpike was one of the earliest line sources analyzed for noise Njturnpike.JPG
The New Jersey Turnpike was one of the earliest line sources analyzed for noise

Roadway noise is the most important example of a linear noise source, since it comprises about 80 percent of the environmental noise exposure for humans worldwide. In the 1960s, when computer modeling of this phenomenon was perfected, the first applications of linear source noise modeling became systematic. After passage of the National Environmental Policy Act and Noise Control Act, [3] the demand for detailed analysis soared, and decision makers began to look to acoustical scientists for answers regarding the planning of new roadways and the design of noise mitigation. The intensity of roadway noise is governed by the following variables: traffic operations (speed, truck mix, age of vehicle fleet), roadway surface type, tire types, roadway geometrics, terrain, micrometeorology and the geometry of area structures.

Due to the complexity of the variables, a line source acoustic model must be a computer model that can analyze sound levels in the vicinity of roadways. The first meaningful models arose in the late 1960s and early 1970s. Two of the leading research teams were BBN in Boston and ESL Inc. of Sunnyvale, California. Both of these groups developed complex mathematical models to allow the study of alternate roadway designs, traffic operations and noise mitigation strategies in an arbitrary setting. [4] Later model alterations have come into widespread use among state Departments of Transportation and city planners, but the accuracy of early models has had little change in 40 years.

Generally line source acoustic models trace sound ray bundles and calculate spreading loss along with ray bundle divergence (or convergence} from refractive phenomena. Diffraction is usually addressed by establishing secondary emitters at any points of topographic or anthropomorphic “sharpness” (such as noise barriers or building surfaces. Meteorology can be addressed in a statistical manner allowing for actual wind rose and wind speed statistics (along with thermocline data).

Water pollution line source

Colorado River, receiving effectively a linear source of silt from the sides of the Grand Canyon. Canyon midday.jpg
Colorado River, receiving effectively a linear source of silt from the sides of the Grand Canyon.

Less common are line source applications in the field of water pollutant dispersal. This phenomenon generally arises when surface runoff scours soil contaminants from upper soil layers and transports these pollutants to a linear receiving water, such as a river. The underlying land management practices which lead to such sources of water pollution are logging, pesticide application, construction grading, slash-and-burn activity and urban stormwater runoff.

Again computer models are needed to address the complexity of such an extended linear discharge into a dynamic medium such as flowing water. The resulting surface runoff water carrying pollutants may be considered a line source discharging into a river or stream. The chemical composition of this surface runoff may be characterized by a surface runoff model such as the USGS runoff precipitation algorithm, [5] while the instream transport may be analyzed by a dynamic river pollutant model such as DSSAM.

Light emission line source

Common T8 fluorescent lighting tubes used in office environments FluorescentT8razorback.jpg
Common T8 fluorescent lighting tubes used in office environments

In the study of illumination, a variety of sources are linear in nature, most commonly the fluorescent tube, During the process of interior lighting design it is important to calculate the light intensity at work stations or other user areas, not only to ensure sufficient light is present, but more importantly to avoid over-illumination and its attendant energy wastage as well as adverse health effects. Thus the scientists involved in light transmission calculations employ computer models that recognize linear sources when fluorescent fixtures are used. In a typical setting there may be hundreds of finite length light sources that comprise the light output in an office environment. A related concept are the ultraviolet tubes used in phototherapy, where output radiation from the tube can be accurately modeled by treating the tube as a line source. [6] On a larger scale, an illuminated roadway may act as a line source of light pollution.

See also

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<span class="mw-page-title-main">Environmental engineering</span> Integration of sciences and engineering principles to improve the natural environment for life

Environmental engineering is a professional engineering discipline related to environmental science. It encompasses broad scientific topics like chemistry, biology, ecology, geology, hydraulics, hydrology, microbiology, and mathematics to create solutions that will protect and also improve the health of living organisms and improve the quality of the environment. Environmental engineering is a sub-discipline of civil engineering and chemical engineering. While on the part of civil engineering, the Environmental Engineering is focused mainly on Sanitary Engineering.

<span class="mw-page-title-main">Environmental science</span> The integrated, quantitative, and interdisciplinary approach to the study of environmental systems.

Environmental science is an interdisciplinary academic field that integrates physics, biology, and geography to the study of the environment, and the solution of environmental problems. Environmental science emerged from the fields of natural history and medicine during the Enlightenment. Today it provides an integrated, quantitative, and interdisciplinary approach to the study of environmental systems.

<span class="mw-page-title-main">Norwegian Institute for Air Research</span>

The NILU – Norwegian Institute for Air Research or NILU is one of the leading specialized scientific laboratories in Europe researching issues related to air pollution, climate change and health. It is an independent nonprofit institution, established in 1969, staffed by scientists, engineers and technicians with specialized expertise for working on air pollution problems. The staff do more than two hundred projects annually for research councils, industries, international banks and local, national and international authorities and organizations. Its first director was Brynjulf Ottar.

<span class="mw-page-title-main">Atmospheric dispersion modeling</span> Mathematical simulation of how air pollutants disperse in the ambient atmosphere

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<span class="mw-page-title-main">Noise barrier</span> Exterior structure on infrastructure used to prevent loud sounds from escaping

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<span class="mw-page-title-main">Nonpoint source pollution</span> Pollution resulting from multiple sources

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<span class="mw-page-title-main">Roadway air dispersion modeling</span> Study of air pollutant transport from a roadway

Roadway air dispersion modeling is the study of air pollutant transport from a roadway or other linear emitter. Computer models are required to conduct this analysis, because of the complex variables involved, including vehicle emissions, vehicle speed, meteorology, and terrain geometry. Line source dispersion has been studied since at least the 1960s, when the regulatory framework in the United States began requiring quantitative analysis of the air pollution consequences of major roadway and airport projects. By the early 1970s this subset of atmospheric dispersion models was being applied to real-world cases of highway planning, even including some controversial court cases.

<span class="mw-page-title-main">Surface runoff</span> Flow of excess rainwater not infiltrating in the ground over its surface

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<span class="mw-page-title-main">Roadway noise</span> Sound energy emanating from motor vehicles

Roadway noise is the collective sound energy emanating from motor vehicles. It consists chiefly of road surface, tire, engine/transmission, aerodynamic, and braking elements. Noise of rolling tires driving on pavement is found to be the biggest contributor of highway noise and increases with higher vehicle speeds.

<span class="mw-page-title-main">Hydrological transport model</span>

An hydrological transport model is a mathematical model used to simulate the flow of rivers, streams, groundwater movement or drainage front displacement, and calculate water quality parameters. These models generally came into use in the 1960s and 1970s when demand for numerical forecasting of water quality and drainage was driven by environmental legislation, and at a similar time widespread access to significant computer power became available. Much of the original model development took place in the United States and United Kingdom, but today these models are refined and used worldwide.

<span class="mw-page-title-main">National Environmental Research Institute of Denmark</span>

The National Environmental Research Institute of Denmark, abbreviated NERI, was an independent research institute under the Ministry of the Environment. It was created in 1989 by merging the existing laboratories of the Environmental Protection Agency, which covered marine, freshwater and air pollution, soil ecology and analytical chemistry, with the Danish Wildlife Research, under the Ministry of Agriculture. The laboratories were physically located on Risø, in Silkeborg and on Kalø, north of Aarhus. In 1995, Greenland Biological Research laboratory was added.

Area sources are sources of pollution which emit a substance or radiation from a specified area.

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<span class="mw-page-title-main">Nutrient pollution</span> Contamination of water by excessive inputs of nutrients

Nutrient pollution, a form of water pollution, refers to contamination by excessive inputs of nutrients. It is a primary cause of eutrophication of surface waters, in which excess nutrients, usually nitrogen or phosphorus, stimulate algal growth. Sources of nutrient pollution include surface runoff from farm fields and pastures, discharges from septic tanks and feedlots, and emissions from combustion. Raw sewage is a large contributor to cultural eutrophication since sewage is high in nutrients. Releasing raw sewage into a large water body is referred to as sewage dumping, and still occurs all over the world. Excess reactive nitrogen compounds in the environment are associated with many large-scale environmental concerns. These include eutrophication of surface waters, harmful algal blooms, hypoxia, acid rain, nitrogen saturation in forests, and climate change.

References

  1. Michael Hogan, Theoretical basis for atmospheric diffusion from a linear source, ESL Inc., Environmental Systems Laboratory, Publication IR-29, Sunnyvale, Ca., May 4, 1970
  2. Richard J. Venti, Atmospheric diffusion models for roadway sources, ESL Inc., Environmental Systems Laboratory, Publication ET-22, Sunnyvale, Ca., October 5, 1970.
  3. Public Law No. 92-574, 86 Stat. 1234 (1972) Noise Pollution and Abatement Act of 1972, codification amended at 42 U.S.C. 4901-4918 (1988)
  4. John Shadely, Acoustical analysis of the New Jersey Turnpike widening project between Raritan and East Brunswick, Bolt Beranek and Newman, 1973
  5. United States Geological Survey runoff precipitation algorithm Archived 2007-06-10 at the Wayback Machine
  6. David Robert Grimes, Chris Robbins, Neil John O'Hare. Dose Modeling in Ultraviolet phototherapy, Medical Physics, 37(10) October 2010