A life-cycle inventory is a process of quantifying energy and raw material requirements, atmospheric emissions, waterborne emissions, solid wastes, and other releases for the entire life cycle of a product, process, or activity.
An inventory analysis produces a list containing the quantities of pollutants released to the environment (after treatment or control) and the amount of energy and material consumed. The results can be segregated by life-cycle stage, media (air, water, and land), specific processes, or any combination thereof.
In the life-cycle inventory phase of an LCA, all relevant data are collected and organized. Without a life-cycle inventory, no basis exists to evaluate comparative environmental impacts or potential improvements. The level of accuracy and detail of the data collected is reflected throughout the remainder of the LCA process. (No predefined list of data quality goals exists for all LCA projects. The number and nature of data quality goals necessarily depend on the level of accuracy required to inform the decision makers involved in the process.)
Resource constraints for data collection may be a consideration in defining the system, although in no case should the scientific basis of the study be compromised. The level of detail required to create a thorough inventory depends on the size of the system and the purpose of the study. In a large system encompassing several industries, certain details may not be significant contributors given the defined intent of the study. These details may be omitted without affecting the accuracy or application of the results. However, if the study has a very specific focus, such as a manufacturer comparing alternative processes or materials for inks used in packaging, it would be important to include chemicals used in very small amounts.
Life-cycle inventory analyses can be used in various ways. The data can assist an organization in comparing products or processes and considering environmental factors in material selection. In addition, inventory analyses can be used in policymaking, by helping the government develop regulations regarding resource use and environmental emissions.
Although much can be learned about a process by considering the life-cycle inventory data, an impact assessment provides a more meaningful basis to make comparisons. For example, although we know that 90001 of carbon dioxide (CO2) and 50001 of methane released into the atmosphere are both potentially harmful greenhouse gases, a life-cycle impact assessment (LCIA) can determine which would have a greater impact. Which is worse? What are their potential impacts on global warming? On smog? Using science-based characterization factors, an LCIA can calculate the impacts that each environmental release may have on problems such as smog or global warming.
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