Emissions Inventory - Stage 4

01 Update your Stage 4 plan

At Stage 4, the emissions inventory (EI) should become a more accurate and policy-relevant system that supports planning, compliance, policy evaluation, and accountability. Update your plan to define objectives, timelines, staffing, and governance arrangements for the next phase of inventory development. At this stage, the inventory team should begin developing country-specific emission factors and using measured emission factors where appropriate, while also improving the use of activity data from stakeholders and existing MRV frameworks. The Stage 4 plan should align inventory outputs with the needs of advanced air quality management. This includes expanding coverage of short-lived climate pollutants (SLCPs), increasing the accuracy and resolution of emission maps, using gridded emissions for refined air quality modeling, supporting policy tracking and accountability, and developing initial emission scenarios and projections. The plan should also identify the key categories or sectors that require advanced emissions methodologies or additional scenario support. EI teams should define milestones for inventory development and performance reviews to track progress over time. As in earlier stages, the plan should be realistic about staffing, data access, institutional authority, and the resources needed to sustain the work.  

Two resources of particular use for this step include the general guidance sections of both the Intergovernmental Panel on Climate Change (IPCC) guidelines from the Task Force for Inventories (TFI), ​including methodologies ​​​​​​on Inventories for Short-lived Climate Forcers​, and the EMEP/EEA air pollutant emission inventory guidebook. Existing IPCC guidelines provide the methodological basis for developing greenhouse gas (GHG) inventories, including guidance on activity data, emission factors, tiered methods, uncertainty analysis, key category analysis, quality assurance/quality control (QA/QC), reporting, and archiving. The European Monitoring and Evaluation Programme/European Environment Agency (EMEP/EEA) Guidebook complements this by providing methods and emission factors for air pollutants such as particulate matter (PM), nitrogen oxides (NOx), sulfur dioxide (SO₂), volatile organic compounds (VOCs), ammonia (NH₃), and black carbon (BC), helping jurisdictions understand what additional information is needed to build an integrated inventory that supports both climate reporting and air quality management.​ It is crucial to look for any updates on methodologies or refinements published by international methodology developers such as the IPCC, EMEP/EEA, etc.​   

02 Secure stable funding and long-term technical capacity

At Stage 4, emission inventory work should be increasingly supported through regular government budgets rather than short-term project funding. An indicative Stage 4 capacity is approximately nine full-time-equivalent staff, including collaborators or contractors, supported by an in-house data server with secure backup. Major central funding should support the core inventory function, although supplementary donor funding may continue to support methodological development, training, or specialized analyses. EI teams should maintain permanent technical staff with clear responsibilities for data collection, compilation, QA/QC, uncertainty assessment, spatial analysis, reporting, and scenario development. Because emission inventory work requires institutional memory, agencies should also implement succession planning and retention strategies. Staff training plans should be updated regularly to reflect new methods, pollutants, software systems, and reporting requirements. Funding should also support the IT, database, software, and computational infrastructure needed for advanced inventory applications. This includes secure data storage, database maintenance, GIS systems, software licenses, version control, data backup, and computing resources needed for gridded emissions, uncertainty assessment, and scenario analysis. ​​UNEP/GEF provides useful training, including information on institutional arrangements. The Inventory of US Greenhouse Gas Emissions and Sinks 1990-2022 (US EPA, 2024) Section 1 also provides useful information on institutional arrangements and an overview of the inventory preparation process; for examples from outside of the US, see National Communications to the UNFCCC. Further EI training can be obtained freely through the UNFCCC (with a nomination from your national focal point) and from the GHG Management Institute. 

03 Refine emission factors and activity data for key categories

​​Use the key category analysis from the previous emission inventory cycle (see Stages 1, 2, and 3 of the Emissions Inventory Guidance if needed) to prioritize improvements in emission factors and activity data. For the sectors and pollutants that dominate emissions, trends, uncertainty, or policy relevance, develop locally derived or measurement-based emission factors where feasible. These improvements should focus first on sources where default values are likely to be poorly representative of local fuel quality, technologies, operating practices, or control measures. Where advanced monitoring data are available, use them to refine assumptions about source profiles and emissions. Facility-level information, subnational activity data, surveys, and administrative datasets can also improve the inventory's accuracy and spatial allocation. Collect and quality-check information on control technologies, fuel quality, abatement implementation, and policy or control measure penetration where these materially affect emissions. Clearly document areas where local data remains insufficient and where further improvement is needed. This documentation will support transparency and help guide the next inventory improvement cycle. Where locally collected activity data are proprietary or commercially sensitive, such as facility-level industrial production, fuel use, or control technology data, agencies should establish clear procedures for internal documentation and external reporting. The underlying data should be retained in sufficient detail for quality checks, recalculations, and technical review, while public-facing reports and visualizations should aggregate or anonymize information where needed to protect confidentiality.  While many existing emission factors are found through literature searches (see Santiago-De La Rosa et al., 2018), existing databases of emission factors include the​ EMEP/EEA, Australia National Pollutant Inventory, ​ US EPA AP-42, and the IPCC Emission Factor Database.  There are also toolkits and guidelines available for emission factor development, for example, from the US EPA and the UK Department for Environment, Food and Rural Affairs.​ It is very important to take into account the national conditions, country practice, industry type practice, etc.​​ 

04 Now incorporating SLCPs, replicate Steps 3-10 from Stage 1 guidance using Tier 2 methods, refined data, and enhanced QA/QC 

Using the refined methods and datasets developed in Stage 4, repeat the core inventory compilation process described in Stage 1. The inventory should now apply Tier 2 methods where feasible, use improved emission factors and activity data, and include enhanced QA/QC procedures throughout the process. Now, EI teams should expand inventory coverage to include SLCPs in addition to greenhouse gases and criteria air pollutants (PM and gaseous pollutants), applying the latest available methodologies and preparing for the implementation of forthcoming or updated guidance​​ (e.g., the IPCC short-lived climate forcer guidelines). Recalculate emissions using updated emission factors and more granular activity datasets, especially for key categories and high-uncertainty sources: re-run uncertainty assessment and key category analysis for each pollutant (see also US EPA inventory report, Sections 1.5 and 1.6). Where ​data-driven ​quantitative uncertainty estimates are not feasible, use ​expert judgment as per the IPCC, or EMEP/EEA methodologies ​to ​determine the uncertainty and run the analysis​. As capacity increases, move from simple error-propagation approaches to Monte Carlo methods to estimate uncertainty (e.g., the GHG Protocol uncertainty assessment). Document all methodological changes, recalculations, splicing methods, and effects on time-series consistency, and maintain full transparency and archiving procedures. 

05 Report to UNFCCC, LRTAP, or other regional agreements 

Stage 4 inventories should be suitable for regular domestic use and consistent international reporting. Ensure that submissions to the UNFCCC, EU, LRTAP, or other relevant regional agreements use the latest approved and documented methods and formats through the authorized national institution or ministry. Improve consistency across domestic and international reporting streams so that the same underlying database and assumptions support multiple reporting needs where possible. This reduces duplication, improves transparency, and makes it easier to explain differences between reporting formats or pollutant groupings. Respond systematically to review findings and incorporate recommendations into the next inventory cycle. Reporting deadlines can also reinforce a regular inventory schedule, support management accountability, and justify sustained resources for inventory improvement.  An example of inventory data prepared for black carbon reporting can be found from EMEP.​ Always look for updated or new methodologies published by the relevant organizations to whom reporting shall be addressed.​ 

06 Generate GIS maps and refined gridded emissions inventories 

At Stage 4, GIS maps and gridded emissions inventories from Step 5 should become routine products of the emission inventory system. Update spatial allocation methods using improved geospatial datasets, facility locations, road networks, land-use data, population data, fuel-use information, and other spatial proxies relevant to local sources. Increase sectoral and spatial resolution where possible and useful. Improve temporal disaggregation to support air quality modeling applications, including seasonal, monthly, daily, or hourly variation where these profiles are important for air quality forecasting, source​ apportionment​​​​​, model validation, and exposure assessment. Publish maps and spatial summaries where appropriate to support stakeholder communication and transparency. Spatial products should be accompanied by clear documentation of methods, assumptions, resolution, limitations, and update history to ensure they are used appropriately by modelers, planners, and public communication teams.  EMEP/EEA provides an ​​overview of spatial emission mapping, and the US EPA provides open-source modeling tools such as SMOKE,​​​​ and Biogenic Emission Inventory System (BEIS). 

07 Develop baseline and policy emissions scenarios

At Stage 4, emission inventories should begin to support prospective policy analysis through baseline and policy emissions scenarios. Develop a reference or business-as-usual (BAU) projection using expected policy, economic, demographic, and activity trends under current policies (see Yarlagadda et al., 2022 for an example from India, ​​Haddad et al., 2018 for an example from Lebanon). This reference scenario should provide the foundation for preparing alternative policy scenario pathways. The initial policy projection should include at least one “with-measures” scenario representing the expected effects of adopted or clearly committed policies relative to the reference or BAU pathway. Note that these scenarios should be aligned with the work described under the Decision Support Guidance, Stage 5, Step 2. See the EMEP/EEA guidance chapter A.8 for scenario/projection development.  

Use clean air action plans, climate action plans, sectoral strategies, Nationally Determined Contributions (NDCs), and other relevant planning documents to identify the policy priorities that should be reflected in the scenario set. In coordination with relevant ministries and agencies, map planned or proposed regulations, fuel switching, technology uptake, control measures, and other interventions that may affect future emissions. Where possible, ensure that modeled measures correspond to policies or instruments that are legally or administratively implementable within the planning horizon.

Develop additional scenarios that reflect plausible policy pathways, such as the full implementation of existing or planned measures, enhanced clean-air measures, climate-aligned measures, or integrated air-quality and climate strategies. Working with ​air dispersion/​air quality models, estimate the expected impacts of, for example, planned regulations, fuel switching, technology uptake, control measures, or other interventions through additional scenarios. Compare alternative policy pathways across sectors and pollutants to understand which measures are expected to deliver the greatest emission reductions or co-benefits. ​Use the output to feed into ​Cost-Benefit Analysis studies and subsequent policy decisions. ​​Use scenarios to inform national planning, policy, and investment decisions in coordination with other government offices.  

Coordinate with the Environmental Impact Assessment and Health Impact Assessment teams to ensure emissions scenarios support natural-capital, ecosystem, exposure, and health-benefit analyses. Where integrated assessment tools (e.g.,​ air quality models coupled to health/economic impact​ ​tools, ​GCAM, GAINS) or simpler models (e.g., CoST, LEAP-IBC) are being developed or expanded, ensure that inventory-based scenarios are consistent with the assumptions, policy scope, and planning horizons used in those tools. 

08 Use the emissions inventory for policy tracking, accountability, and compliance

At Stage 4, the emissions inventory should be used actively to track progress against national emissions ceilings or targets, sector commitments, and implemented air quality measures. Inventory results can help determine whether measures are reducing emissions as expected and whether additional action is needed. Use sectoral and spatial emissions data to identify underperforming sectors or regions that require corrective action. Communicate relevant findings to Decision Support processes so that policy options can be reassessed using the best available evidence. ​​​​Inventory outputs can also help assess where air pollution sources or impacts co-occur with other environmental stressors. Transparent public reporting, developed in cooperation with Public Engagement & Communication teams, can strengthen accountability and help stakeholders understand the basis for air quality decisions. EMEP/EEA provides a chapter on Projections (Part A.8) detailing institutional arrangements for air pollutant projections reporting, as does the US EPA guidance (Chapter 5). 

09 Establish a formal 1–2-year update cycle

By Stage 4, the emission inventory should operate on a formal update cycle. Establish regular inventory updates on an annual or biennial basis, depending on reporting requirements, data availability, and institutional capacity. The update schedule should be fully documented. Major methodological updates should also be scheduled at a regular cadence. Maintain version control, documentation, and a history of recalculations to distinguish changes in emissions from changes in methods. ​K​ey category analysis and uncertainty assessment should guide the priority improvements for the next cycle, including methodological upgrades and data investments. After each update cycle, conduct a management review to assess inventory quality, timeliness, resource needs, and priority improvements. This review helps institutionalize continuous improvement and ensures that the inventory remains useful for reporting, modeling, and policy evaluation.  The UNEP/GEF training and EMEP/EAA guidance (Chapter A.6) provide an overview of the ​​emissions inventory development cycle and reporting processes, including those set by the UNFCCC, which guide submissions of updated emissions reports.