Emissions regulatoryframeworks vary from economy to economy, depending.largely on geographic location, climate, population density, and degree of.industrialisation. Emissions regulations may be set at the national, state or local levels, and may therefore vary at v~ious sites in an economy. Whereas the emphasis in this study is on national standards or guidelines. information on state and/or local standards is included where appropriate.There are two basic, but interrelated approaches used for atmospheric emissions of coal-based air pollutants. One approach is based on the level of ambient concentration of the pollutants in the atmospheric environment surrounding the source. The other approach relates to the maximum level of absolute emissions of pollutants permitted at the source.

There is a direct relationship between the two approaches, as the level of emissions of pollutant at source correlates with the ambient concentration of the same pollutant. However, the ambient concentration is also determined by such factors as the effective chimney height, the prevailing meteorological (wind, temperature, humidity, etc) and topographical conditions, the point of measurement and, also importantly, other sources of emissions. Often, both ambient quality and emissions standards arc used in tandem.

Ambient air quality goals are quoted as maximum permissible levels of the pollutant in ambient air in micrograms per cubic metre (ug/nr') at atmospheric pressure and 0°C; goals can be set over a long term (annual) or a short term (daily and/or hourly). Ambient air quality goals alone have often been found inadequate as industrial activity in a region increasesor becomes varied.

Emissions standards at sources are then additionally required; these standards are quoted as mass of the pollutant in a normalised volume of stack gas, usually in milligrams per normal cubic metre (mg/Nm ') at atmospheric pressure, 0°C and at a given oxygen level so as to ensure that the control is not achieved by air dilution. In some economies, these standards are specified as mass of the pollutant per unit of specific energy of the fuel used, e.g., pounds per million British thermal units (lb/MBtu) or grams per gigajouletg/Gf).

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