How do process-based and input-output-based life cycle inventory methods compare?

Process-based and input-output-based life cycle inventory (LCI) methods differ in their approach to quantifying environmental impacts. Process-based LCI focuses on detailed data from individual processes within a product life cycle providing a precise and accurate assessment of specific activities. Input-output-based LCI utilizes aggregated data on economic transactions across entire sectors, offering a broader, more comprehensive view of interconnected supply chains. Process-based methods are resource-intensive but offer granularity, while input-output methods are more efficient but may lack specificity.

Process-based Life Cycle Analysis (P-LCI) is an approach that meticulously tracks the physical flows of materials and energy through all stages of a product or process's life, from raw material extraction to processing in the end of useful life. Although it provides detailed information on environmental performance, P-LCI requires the identification and modeling of each unitary process at the system boundary and the collection of data from primary or secondary sources. It is a valuable tool for assessing sustainability, but its implementation can be time-consuming, data-intensive and prone to errors, especially at system boundaries.

In general process-based LCI offers detailed insights into specific processes but requires extensive data, while input-output-based LCI provides a more holistic view of the economy but may compromise detail and accuracy at the process level.

Input-Output based Life Cycle Assessment (IO-LCI) is a valuable approach to analyze economic transactions between sectors while considering environmental impacts. By using input-output tables, it overcomes data gaps and allocation issues present in conventional Life Cycle Assessment (P-LCI) by capturing indirect impacts. Although it brings advantages, IO-LCI has limitations, such as aggregation levels, temporal and spatial resolution, and environmental coverage of the tables. Choosing the appropriate methodology is fundamental, considering the characteristics of the study and sustainability objectives.

Hybrid Life Cycle Inventory (H-LCI) emerges as a transformative approach, synergizing the strengths of Process Life Cycle Inventory (P-LCI) and Input-Output Life Cycle Inventory (IO-LCI). By ingeniously blending these methodologies, H-LCI optimizes precision. It strategically employs P-LCI for the focal system, delving into the intricacies while harnessing IO-LCI for the periphery, encapsulating the supportive upstream and downstream dynamics. H-LCI doesn't merely stop at integration; it's versatile, utilizing IO-LCI to validate P-LCI or vice versa, thereby ensuring a comprehensive and accurate Life Cycle Inventory. Yet, its potential is challenging. Methodological challenges loom, ranging from data compatibility to consistency.

- **Process-Based:** - Detailed analysis of individual processes. - Requires specific data for each stage. - Granular understanding of environmental impacts. - Resource-intensive due to detailed data needs. - **Input-Output-Based:** - Examines overall flows across the entire economy. - Uses aggregated data from economic tables. - Provides a systemic view capturing indirect impacts. - Less data-intensive, offering a comprehensive perspective.