Differentiate between the 'impact assessment' and 'inventory analysis' phases of a Life Cycle Assessment, stating the primary output of each.

Life Cycle Assessment (LCA) is a systematic methodology for evaluating the environmental impacts associated with a product, process, or service throughout its entire life cycle. Within an LCA, the 'inventory analysis' and 'impact assessment' phases serve distinct but sequential purposes.

Inventory Analysis is the second phase of a Life Cycle Assessment, following the definition of goal and scope. During this phase, all relevant quantifiable inputs and outputs of a product system across its entire life cycle are identified and documented. This involves collecting comprehensive data on all energy and raw material inputs consumed, and all emissions to air, water, and soil, as well as waste generation, at each stage from raw material extraction, through manufacturing, transportation, use, and end-of-life management. For example, for a smartphone, inventory analysis would quantify the electricity used to manufacture its components, the water consumed in processing raw materials like copper, and the carbon dioxide emitted during shipping. These individual inputs and outputs are known as 'elementary flows' because they represent direct interactions with the environment, such as the extraction of crude oil or the emission of methane. The primary output of the inventory analysis phase is a comprehensive, quantitative list of these elementary flows linked to the functional unit defined for the study. This list details every environmental input and output associated with the product or system, but it does not yet interpret their environmental significance.

Impact Assessment, also known as Life Cycle Impact Assessment (LCIA), is the third phase of a Life Cycle Assessment, directly following the inventory analysis. Its purpose is to evaluate the significance of the potential environmental impacts using the elementary flow data compiled during the inventory analysis. This phase involves translating the raw inventory data into more meaningful environmental impact indicators. It typically proceeds through several mandatory steps: first, 'classification,' where elementary flows are assigned to specific 'impact categories' (e.g., carbon dioxide, methane, and nitrous oxide are classified under the 'climate change' impact category). Second, 'characterization,' where the classified elementary flows are converted into a common unit for their respective impact category using 'characterization factors.' For instance, different greenhouse gases are converted into carbon dioxide equivalents (CO2-eq) to represent their cumulative contribution to global warming potential. The impact assessment determines how much the quantified emissions and resource extractions contribute to various environmental problems. The primary output of the impact assessment phase is a set of quantified environmental impact indicator results, expressed as potential contributions to various impact categories such as global warming potential (e.g., in kg CO2-eq), acidification potential (e.g., in kg SO2-eq), or eutrophication potential (e.g., in kg PO4-eq). These results indicate the potential magnitude of specific environmental problems associated with the product or system, providing an aggregated and interpreted view of the environmental performance.