Critical review of exergy-based indicators for the environmental impact of emissions

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.