GWP accounts for the total emissions from greenhouse gases such as CO2 (carbon dioxide), CH4 (methane), and N2O (nitrous oxide). The amount of CH4 and N2O is converted into CO2 equivalents by utilizing the characterization factors (36.75 for CH4 and 298 for N2O respectively).

GWP emissions occur from activities like coal combustion, production processes, landfilling, and fertilizer use in soil.

A 100-year time horizon is usually used, and the units are referred to as CO2 equivalents.

The ozone layer is an atmospheric layer that protects us from the sun’s harmful radiation.

Halogens such as chlorine, bromine, and fluorine (Cl, Br, F) are highly reactive and are responsible for ozone depletion. Consequently, the units are described in terms of Chlorofluorocarbons (CFCs).

The characterization factors for each gas are predetermined and used during calculation. For example, 1 kg of methyl bromide is equivalent to 0.57 kg of CFC - similar to the approach taken for greenhouse gases in the Global Warming section above.

EN15804+A2 & EF: mol H+ eq

The acidification impact category quantifies the amount that each gas contributes to acid rain, a cause of acidity (measured in pH) change in soil.

Gases like NH3 (ammonia), SO2 (sulfur dioxide), and NO2 (nitrogen dioxide) contribute to acid rain. Consequently, the impact category unit is expressed in kilograms sulfur dioxide equivalents (kg SO2-eq). The acidification potential of other gases is converted into SO2-eq by using a characterization faction - like 1 kg of NH3 is equal to 1.6 kg of SO2.

Aquatic eutrophication refers to the nutrient enrichment of aquatic environments which impacts water quality by promoting excessive plant growth. In the summer this often manifests as algae blooms in lakes due to nutrient influx.

Nutrient inputs, particularly phosphorus (P) and nitrogen (N), drive the proliferation of plankton and algae in water bodies. Therefore, measurements typically represent amounts of P, N, or their compound forms, such as phosphate (PO4).

EN15804 and EF distinguish between three levels of eutrophication (terrestial, marine, freshater), while the CML and TRACI methods group them.

CML: kg C2H4-eq (C2H4: ethylene)

TRACI: kg O3-eq (O3: ozone)

EN15804+A2 and EF: kg NMVOC (NMVOC: non-methane volatile organic compounds)

In the lower air layers of Earth's atmosphere, volatile organic substances (except methane) and NOx (nitrogen oxides) can undergo photochemical oxidation, leading to smog.

The potential for smog formation depends on the amount of reactants present in the air or the products formed from these reactions. Therefore, smog potential is measured in units that reflect these factors (ozone forms from the reaction between oxygen radicals and O2).

Resource consumption is an important sustainability indicator, especially when the resources used are scarce.

This category can be measured in two ways: mineral consumption (kg SB-eq), and fossil fuel consumption (MJ) for energy generation.

Antimony (Sb), a rare earth element, is used to quantify mineral loss due to human activities. For energy generated from fossil reserves, megajoules (MJ) are the standard unit of measurement.

Figure 2 helps conceptualize this impact category further.

Learn more about this impact category here.

This method measures the potential reduction of available water for human or ecosystem use. It uses the AWARE (Available WAter REmaining) method, which calculates the water remaining per unit of surface area in a given watershed, relative to the world average, after meeting human and aquatic ecosystem demands. The resulting Characterization Factor (CF) ranges from 0.1 to 100 and is meant to be multiplied by the local water consumption inventory.

Human toxicity

Ecotoxicity

Due to a lack of more accurate information, the characterization factor for human toxicity impacts (also known as human toxicity potential) is expressed in comparative toxic units (CTUh), which are the estimated increases in morbidity in the total human population per unit mass of a chemical emitted. This is done by either assuming equal weighting between cancer and non-cancer or by using the USEtox model - developed by UNEP-SETAC Life Cycle Initiative - which classifies the pollutants into carcinogenic and non-carcinogenic to bring out more granularity in the analysis.

TRACI brings out the granularity in the measurement with more sub-categories, such as carcinogenic and non-carcinogenic pollutants in the human toxicity category.

The potentially affected proportion of species (PAF), integrated over time and volume, is an estimate of the potential harmful effects of chemicals in freshwater ecosystems.