Air Pollution Air Quality Air Dispersion

by Bindu
(hyderabad)

Air pollution dispersion modeling is the mathematical simulation of how air pollutants disperse in the ambient atmosphere. It is performed with computer programs, called dispersion models, that solve the mathematical equations and algorithms which simulate the pollutant dispersion. The dispersion models are used to estimate or to predict the downwind concentration of air pollutants emitted from emission sources such as industrial plants and vehicular traffic. Such models are important to governmental agencies tasked with protecting and managing the ambient air quality. The models are typically employed to determine whether existing or proposed new industrial facilities are or will be in compliance with the National Ambient Air Quality Standards (NAAQS) in the United States and similar standards in other nations. The models also serve to assist in the design of effective control strategies to reduce emissions of harmful air pollutants.

The dispersion models require the input of data which includes:

Meteorological conditions such as wind speed and direction, the amount of atmospheric turbulence (as characterized by what is referred to as the stability class, the ambient air temperature and the height to the bottom of any temperature inversion that may be present aloft.
Emissions parameters such as source location and height, source vent stack diameter and exit velocity, exit temperature and mass flow rate.
Terrain elevations at the source location and at the receptor location.
The location, height and width of any obstructions (such as buildings or other structures) in the path of the gaseous emission plume.
Many of the modern, advanced air pollution modeling
programs include a pre-processor module for the input of meteorological and other data, and many also include a post-processor module for graphing the output data and/or plotting the area impacted by the air pollutants on maps. Currently, the AERMOD air pollution dispersion model is the preferred regulatory model of the U.S. Environmental Protection Agency.

The air pollution dispersion models are also known as atmospheric dispersion models, atmospheric diffusion models, air dispersion models and air quality models.

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 were being applied to real world cases of highway planning, even including some controversial court cases.

Air pollution is not a recent phenomenon. The remains of early humans demonstrate that they suffered from the detrimental effects of smoke in their dwellings. The classical writers make reference to air pollution in the ancient cities of Rome and Athens, and there is evidence that the major cities of Europe experienced air pollution problems as far back as medieval times.

However, it was with the development during the Industrial Revolution of increasingly large-scale industries based on new sources of energy—the fossil fuels, coal, oil, and gas—that the deleterious effects of air pollutants on human health and well-being really started to become apparent. The problems were most acute in the large cities that sprang up in the 1800s in Europe and North America, especially where industry and workers' dwellings were in close proximity. In spite of public complaint, there was at this time widespread and passive acceptance of air pollution as an inevitable evil. It was the price to be paid for progress and opportunity.

Attitudes began to change in the middle of the twentieth century. Rapid postwar economic expansion in the late 1940s and early 1950s, coupled with tremendous growth in the use of petroleum products, particularly petrol-driven road vehicles, meant that air pollution became an inescapable part of urban life almost everywhere. Severe air pollution episodes occurred with increasingly regularity in cities in both North America and Europe; these episodes coincided with increased rates of respiratory morbidity and higher than usual death rates. Of these episodes, those that occurred in Donora, Pennsylvania, in 1948 and in London in 1952 are without doubt the most notorious. In the case of the 1952 London episode, poor air quality is believed to be the cause of over four thousand excess mortalities over a five-day period. It was these events that lead the public to demand less polluted air in its cities and provided the driving force for the implementation of measures to control pollutant emissions. The U.K. Clean Air Act, introduced in 1956, is especially noteworthy in this regard, as it was the first legal instrument of its kind and a model for similar legislation in many other countries.

Barry's Response - Everything Wikipedia has to say about the subject, all in one place. Gee, Thanks Bindu.