Life Cycle Impact Assessment: Calculating Environmental Impacts

In previous posts, we described how to construct a model of the manufacture, transportation, use, and disposal of a product from unit processes and reference flows. This process is Life Cycle Inventory (LCI) analysis. According to the ISO 14040 standard on LCA, Life Cycle Inventory (LCI) is the “phase of life cycle assessment involving the compilation and quantification of inputs and outputs for a product throughout its life cycle.”

If one was trying to design a product, constructing a LCI would be the sole exercise needed. However, LCA practitioners need to calculate the environmental impacts of a product. So, we need a way to take our LCI model and transform it into a quantitative estimate of environmental impacts. Some environmental impacts can be calculated by hand. The amount of CO2 produced from the burning of natural gas can be calculated by hand. However, quantifying all the air emissions arising from the refining of oil to make plastic is something that would be very challenging without the help of computer technologies. Luckily, the LCA field is endowed with some good Life Cycle Impact Assessment (LCIA) models which take all unit processes and reference flows of the LCI and transform them to concrete environmental impacts. The Life Cycle Impact Assessment (LCIA) is a “phase of life cycle assessment aimed at understanding and evaluating the magnitude and significance of the potential environmental impacts for a product system throughout the life cycle of the product,” according to the ISO 14040 standards. There are over 10 LCIA models used in the LCA field, and the European Commission Joint Research Center produced a good review of the different LCIA models.

For this LCA, the impacts of the production, transport, use, and disposal of cloth handkerchiefs and paper facial tissues were evaluated by calculating the Climate Change, Human Health, Ecosystem Quality, and Resources impact categories as defined by IMPACT 2002+. IMPACT 2002+ was selected as the LCIA given its wide use in the field and since it first calculates the environmental impacts of 15 more detailed categories (midpoint indicators), and then summarizes the midpoint categories into the 4 endpoint categories. This allows the details of environmental impacts to be assessed while still getting a comprehensive view of ecological impacts.

The 15 midpoint categories calculated by IMPACT 2002+ are: Human Toxicity, Respiratory Effects, Ionizing Radiation, Ozone Layer Depletion, Photochemical Oxidation, Aquatic Ecotoxicity, Terrestrial Ecotoxicity, Aquatic Acidification, Aquatic Eutrophication, Terrestrial Acidification/Nutrification, Land Occupation, Global Warming, Non-Renewable Energy, and Mineral Extraction. All the emissions that affect a midpoint category are summed and expressed as an amount of a key pollutant or energy quantity for that category. For the midpoint damage category of Global Warming, for example, all emissions of greenhouse gases such as carbon dioxide, methane, water vapor, nitrous oxide, and CFCs are converted to carbon dioxide equivalents (CO2-eq).

The midpoint categories are further grouped into the 4 endpoint categories. The Human Health endpoint category is a sum of the midpoint categories that address carcinogenic and non-carcinogenic toxicity to humans (Human Toxicity), respiratory effects in humans (Respiratory Effects and Photochemical Oxidation), Ionizing Radiation, and Ozone Layer Depletion. It is expressed in Disability Adjusted Life Years (DALY), which represents a measure of the loss of “healthy” years of life due to premature death or disability. Although climate change will likely have effects on human health, IMPACT 2002+ does not model them due to high uncertainty in estimating the effects at the time that the model was designed.

Ecosystem Quality sums the midpoint categories that quantify Aquatic and Terrestrial Ecotoxicity, Aquatic Acidification and Eutrophication, Terrestrial Acidification/Nitrification, and Land Occupation. It is expressed in the unit of Potentially Disappeared Fraction of species (PDF) per square meter per year (PDFx m^2 x yr) (Jolliet et al., 2003). PDF x m^2 x yr is the percentage of species that disappear from one square meter of earth surface during one year.

The Resources category sums the energy requirements (in megajoules, MJ) of Non-Renewable Energy and Mineral Extraction along with the extra energy it will take to extract those resources in the future since there will be less of them due to present consumption (Jolliet et al. 2003). The Climate Change endpoint category only sums the impacts of the Global Warming midpoint category, and therefore, provides a good summary of the carbon footprint.

In the next post, we will describe uncertainty analysis – how we vary the assumptions in our LCA to test whether our conclusions are robust.