Key Takeaways & Executive Findings
- •• • Paper recyclables exhibit GHG emission factors ranging from -3,140 to 270 kgCO2-eq·t⁻¹; corrugated cardboard and writing paper show higher absolute values (up to -3,140 kgCO2-eq·t⁻¹) than packaging paper, indicating greater emission reduction potential per tonne, which is critical for prioritizing recycling streams. • • Plastic recyclables show EFs from -3,096 to -566 kgCO2-eq·t⁻¹; EPS demonstrates the highest reduction potential (-3,096 kgCO2-eq·t⁻¹), followed by PET and PVC, while HDPE, LDPE, PP, and other plastics have lower absolute values, guiding material-specific recycling incentives. • • Variability in EFs within the same recyclable category is driven by functional unit definition, system boundary, electricity emission factor, and calculation assumptions; selecting mismatched EFs can lead to accounting errors exceeding 100%, emphasizing the need for scenario-specific data. • • Data gaps persist for LDPE, EPS, and other plastics, with limited studies and even WARM lacking EFs for these materials; this hinders accurate accounting in engineering applications, necessitating additional experimental or field measurements to refine EF ranges.
Abstract
Recyclables constitute a significant fraction of municipal solid waste (MSW) and hold substantial potential for resource utilization and greenhouse gas (GHG) emission reduction, contributing to carbon peak and carbon neutrality goals. However, reported GHG emission factors (EFs) for various recyclables vary widely across databases and literature, ranging from -19,110 to -125 kgCO2-eq·t⁻¹, with significant differences both among categories and within the same category, complicating accurate accounting. This study systematically integrates literature data on EFs for different recyclable categories, focusing on identifying factors causing intra-category variability. Data were collected from global databases (ecoinvent, WARM, CPCD, NAEI) and peer-reviewed studies over the past two decades, normalized to a functional unit of 1 tonne of recyclable. Statistical analysis (mean ± standard deviation) provided reference ranges for each category. Results show paper recyclables EFs range from -3,140 to 270 kgCO2-eq·t⁻¹, with corrugated cardboard and writing paper exhibiting higher absolute values than packaging paper due to structural strength and resource value. Plastic recyclables EFs range from -3,096 to -566 kgCO2-eq·t⁻¹, with EPS showing the highest reduction potential, followed by PET and PVC, then HDPE, LDPE, PP, and other plastics. Key influencing factors include functional unit definition, accounting scenario, system boundary, electricity emission factor selection, and calculation assumptions. The study recommends selecting EFs matching the specific accounting scenario and performing error analysis. Data gaps remain for LDPE, EPS, and other plastics, necessitating further experimental or field data. To enhance accuracy, calibration methods such as process-level and life-cycle inventory data calibration are proposed. This work provides a scientific basis for EF selection and calibration in GHG accounting of recyclables.
1. Introduction
Municipal solid waste (MSW) generation is escalating globally, with projections indicating an increase from 2.1×10⁹ t in 2023 to 3.8×10⁹ t by 2050 if no effective measures are taken. Recyclables constitute 20%–51% of MSW by mass depending on regional income levels, and their proportion rises with economic development. For instance, Shanghai reported recyclables comprising 23.1% of total MSW collected in 2024. The resource recovery of recyclables offers substantial GHG mitigation potential; PROJECT DRAWDOWN estimates global emission reductions of 5.5×10⁹–6.0×10⁹ t CO2-eq between 2020 and 2050. However, accurate quantification of these benefits is hampered by the wide variability in emission factors (EFs) reported across databases and literature, ranging from -19,110 to -125 kgCO2-eq·t⁻¹. This variability arises from differences in accounting methodologies, system boundaries, and regional factors, making it challenging to select appropriate EFs for reliable GHG accounting.
Existing accounting methods—emission factor, mass balance, and direct measurement—each have limitations. Mass balance requires extensive data and is complex for industrial processes; direct measurement is costly and technically demanding. The emission factor method is preferred for its simplicity and cost-effectiveness, but its accuracy hinges on the selection of suitable EFs. This study addresses the bottleneck by systematically compiling and analyzing EF data for various recyclable categories from global databases and literature over the past two decades. It identifies key factors causing intra-category variability and proposes reference ranges and calibration strategies, thereby providing a scientific foundation for selecting and adjusting EFs in GHG accounting of recyclables.
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YANG Xuerui, LU Tao, LV Fan, ZHANG Hua, HE Pinjing (2026). Comparative Analysis of Greenhouse Gas Emission Factors for Recyclables from Municipal Solid Waste. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202509051
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Frequently Asked Questions
What are the primary sources of variability in greenhouse gas emission factors for the same recyclable category, and how can they be minimized in accounting?
Variability arises from differences in functional unit definition, accounting scenario (e.g., recycling process type), system boundary (e.g., including collection and sorting), electricity emission factor selection (regional vs. national grid), and calculation assumptions (e.g., allocation methods). To minimize, select EFs that match the specific accounting scenario and perform sensitivity or error analysis. Calibration methods such as process-level calibration and life-cycle inventory data calibration can reduce deviations.
Which recyclable categories exhibit the highest greenhouse gas reduction potential per tonne, and what are the numerical ranges?
Among plastics, EPS shows the highest reduction potential with an EF of -3,096 kgCO2-eq·t⁻¹, followed by PET and PVC. For paper, corrugated cardboard and writing paper have EFs up to -3,140 kgCO2-eq·t⁻¹, indicating higher reduction potential than packaging paper. These values are based on the mean ± standard deviation from compiled data.
How do the emission factors for recyclables in this study compare with those from major databases like WARM or ecoinvent?
The study integrates data from multiple databases, including WARM and ecoinvent, and reports ranges that encompass their values. For example, paper EFs range from -3,140 to 270 kgCO2-eq·t⁻¹, which includes WARM's values for specific paper types. However, discrepancies exist due to differences in system boundaries and regional factors, highlighting the need for careful selection.
What are the implications of data gaps for LDPE, EPS, and other plastics on engineering-scale GHG accounting?
Data gaps for LDPE, EPS, and other plastics mean that no reliable EFs are available for these materials in many databases, including WARM. This forces practitioners to either extrapolate from similar materials or omit these categories, leading to incomplete or inaccurate accounting. The study recommends collecting more experimental or field data to establish robust EFs for these materials.
What calibration methods are proposed to improve the accuracy of emission factor-based accounting for recyclables?
The study suggests two calibration approaches: (1) process-level calibration, which adjusts EFs based on specific operational parameters of the recycling facility, and (2) life-cycle inventory data calibration, which refines input data such as energy consumption and material losses. These methods help reduce deviations between literature EFs and actual scenarios, enhancing accounting reliability.
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