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Exergy-based indicators for the environmental impact of emissions are critically reviewed, in part by comparing them with other indicators for the environmental impact of emissions.The work highlights the potential for exergy to be, or provide the basis for, an effective indicator of the potential of an emitted substance to impact the environment. Relations examined between environmental impact and exergy in general and the chemical exergy of waste emissions in particular support the use of exergy as such an indicator. The measure provided by exergy of disequilibrium with respect to a reference environment is considered, along with the consequence that the exergy of unrestricted waste emissions has the potential to impact on the environment. Exergy is observed to exhibit many of the characteristics of other indicators of environmental impact, which are mainly empirical in nature. An exergy-based indicator could contribute to the development of rational and objective procedures for assessing harmful effects on the environment and predicting environmental impact potential for a substance. The potential usefulness of exergy in addressing environmental problems, although significant, requires further investigation before widely accepted exergy-based indicators of the environmental impact potential of a substance are developed. INTRODUCTIONExergy analysis is a thermodynamic technique for assessing and improving systems and processes, which is similar but advantageous to energy analysis, in large part because it is based on the second law of thermodynamics. The exergy of an energy form or a substance is a measure of its usefulness.Exergy can be applied beyond thermodynamics to understanding waste emissions and reducing their environmental impact because exergy can also be viewed as a measure of the departure of a substance from equilibrium with a specified reference environment, which is often modeled as the actual environment. For clarity, a waste emission is defined here as a release to the environment of a material not considered usable. Furthermore, exergy is a measure of potential of a substance to cause change. The exergy of an emission to the environment, therefore, is a measure of the potential of the emission to change or impact the environment. The greater the exergy of an emission, the greater is its departure from equilibrium with the environment, and the greater may be its potential to change or impact the environment. The exergy of an emission is zero only when it is in equilibrium with the environment and thus benign. These points suggest that exergy may be, or provide the basis for, an effective indicator of the potential of an emission to impact the environment.This article discusses the potential of exergy as an indicator for the environmental impact of waste emissions, and critically reviews such indicators. To support the arguments, the relations between exergy and the environment are described, and exergy is compared with other indicators for the environmental impact of waste emissions. It is demon...

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