Environmental comparison metrics for life cycle impact assessment and process design

Metrics (potentials, potency factors, equivalency factors or characterization factors) are available to support the environmental comparison of alternatives in application domains like process design and product life-cycle assessment (LCA). These metrics typically provide relative insights into the implicit concern associated with chemicals, emissions and resource consumption in the context of human health, ecological health and resource depletion. The approaches used to derive the metrics range in their Site-specificity, complexity, comprehensiveness, sophistication and uncertainty. It is therefore often necessary to consider the use of more than one approach within the context of a given impact category to help support a decision. In this paper we outline some of the strengths and weaknesses of available approaches in the commonly considered categories of global warming, stratospheric ozone depletion, tropospheric ozone (smog) creation, eutrophication/nutrification, acidification, toxicological impacts and resource depletion.